CABI SILWOOD LIBRARY

24 0066169 2

I N S E C T H E R B I V O R E L O A D

A N D

P L A N T S U C C E S S I O N

G A R E T H E D W A R D S - J O N E S

B . S c . ( H o n s ) M a n c h e s t e r

A t h e s i s s u b m it t e d f o r th e d e g r e e o f

D o c t o r o f P h i lo s o p h y o f th e

U n i v e r s i t y o f L o n d o n a n d f o r th e

D ip lo m a o f Im p e ria l C o l le g e

D e p a r t m e n t o f P u r e a n d A p p l i e d B io lo g y

Im peria l C o l le g e

S i lw o o d P a r k

A s c o t

B e r k s h i r e S e p t e m b e r 1988

T A B L E O F C O N T E N T S

S u m m a r y 1L is t o f f ig u r e s 7.L is t o f ta b le s 3

C H A P T E R 1 : I n t r o d u c t io n 171 . 1 O v e r v i e w 171 . 2 . i H o s t p l a n t s p a t ia l d i s t r ib u t i o n 181 , 2 . i i H o s t p la n t d e n s i t y 191 . 2 . ii P a tc h c o m p o s it io n

1 91 .3 N u t r i e n t a v a i l a b i l i t y in th e h o s t p la n t 201 .4 C h e m ic a l d e fe n c e s 211 . 4 , i C y a n i d e 221 .4 . ii A lk a lo id s 231 . 4 . i i i G lu c o s in o la t e s 261 , 4 . i v F la v e n o id s 281 . 4 . v S a p o n in s 281 , 4 . i v T e r p e n e s & R e s in s 291 . 4 . v i i T a n n i n s 311 , 4 . v i i i M is c e l la n e o u s d e f e n c e s 331 .5 R e v ie w o f p la n t / h e r b iv o r e c o m m u n it y a n d

e v o l u t i o n a r y t h e o r y

34

C H A P T E R 2: M e th o d s 442 . 1 E x p e r im e n t a l s i t e s 442 . 1 . i S i te p r e p a r a t io n 442 . 1 . i i S i te a g e a n d n o m e n c la tu r e 442 . 1 . iii M a r k i n g s i te s 452 . 2 S a m p l in g 462 . 2 . i I n s e c t s a m p l in g 472 . 2 . i i P la n t s a m p l in g 482 .3 D ata h a n d l in g a n d a n a ly s is 502 . 3 . i R a t io n a le b e h in d d a ta b a s e 502 . 3 . ii D i s t r i b u t i o n o f th e data 522 . 3 . iii Gamma d i s t r i b u t i o n 522 . 3 . iv G e n e r a l i s e d l in e a r in t e r a c t iv e m o d e ls (G L I M ) 532 . 3 . v O t h e r s t a t i s t i c s 56

C H A P T E R 3: C o m m u n ity P a t t e r n s T h r o u g h S u c c e s s io n 573.1 I n t r o d u c t i o n 573 .2 M e th o d s 593.3 R e s u l t s 603.3. a P la n t c o m m u n it y 603.3. a . i P la n t s p e c i e s c o m p o s it io n 653 . 3 . a . i i L e a f a r e a a n d th e p la n t co m m u n ity 65

T o ta l le a f a re a

A n n u a l f l u c t u a t i o n s in le a f a re a in a s e r a i s t a g e

T r e n d s in th e le a f a re a o f m ajor p la n t fam il ie s

w ith in a n d b e tw e e n s e r a i s ta g e s

P r o p o r t io n o f s e r a i s t a g e le a f a r e a , p r o v i d e d b y

e a c h m ajo r p la n t fa m ily

C o n t r i b u t i o n o f in d i v i d u a l p la n t s p e c ie s to th e

tota l le a f a r e a o f a s e r a i s ta g e

3 . 3 . b . I n s e c t C o m m u n it y 843 . 3 . b . i T o ta l i n s e c t a b u n d a n c e d u r i n g s u c c e s s io n 843 . 3 . b . i i A b u n d a n c e o f m ajo r h e r b i v o r e ta x a a s s o c ia t e d w ith 84

d i f f e r e n t s e r a i s t a g e s

3 . 3 . b . i i i A n n u a l v a r ia t i o n in in s e c t a b u n d a n c e 8 6

T o ta l n u m b e r s

A d u l t n u m b e r s

3 . 3 . b . i v A n n u a l v a r ia t i o n in a b u n d a n c e o f in s e c t g r o u p s 923.3. b . v H e r b i v o r e s p e c i e s c o m p o s it io n 92

V a r i a t i o n in s p e c ie s r i c h n e s s w ith s e r a i s t a g e

A n n u a l v a r ia t i o n in s p e c ie s r i c h n e s s

A n n u a l v a r ia t i o n in s p e c ie s r i c h n e s s o f in s e c t

g r o u p s

S p e c ie s r i c h n e s s o f in s e c t g r o u p s f e e d in g on

m ajor p la n t fa m il ie s

3 . 3 . b . v i V a r ia t io n in in s e c t s p e c ie s c o m p o s it io n w ith 100s u c c e s s io n a l a g e

A n n u a l v a r ia t i o n in in s e c t h e r b i v o r e s p e c ie s

c o m p o s it io n

3 . 3 . b . v i i T h e b i r c h c o m m u n ity

V a r ia t io n in s p e c i e s r i c h n e s s b etw een c a n o p ie s

a n d y e a r s

P r o p o r t io n o f a d u l t in d i v i d u a l s in each in s e c t

g r o u p

V a r ia t io n in a b u n d a n c e o f O n c o p s is b e tw e e n

c a n o p ie s a n d d a t e s

1 0 2

3 .4 D is c u s s io n 1 0 5

C H A P T E R 4: A b s o lu t e A b u n d a n c e o v e r a S u c c e s s io n a l G r a d i e n t 1 1 0

4.1 I n t r o d u c t io n1 1 0

4 .2 M e th o d s i n

4 .3 R e s u lt s 1 1 2

4 . 3 . i D i s t r ib u t io n o f a b s o lu t e a b u n d a n c e 1 1 2

4 . 3 . ii A b s o lu t e a b u n d a n c e in r e la t io n to s e r a i s ta g e

C ic a d e l l id a e

D e lp h a c id a e

C u r c u i io n o id e a

H e t e r o p t e r a

M in o r in s e c t g r o u p s - P s y l l id a e , C e r c o p i d a e ,

C h r y s o m e l id a e

1 1 2

4 . 3 . ii i A b s o lu t e a b u n d a n c e o f w o o d y a n d n o n - w o o d y 1 2 6

p la n t s

4 . 3 . iv A b s o lu t e a b u n d a n c e on m ajor p la n t fam ilies 1 2 6

4 . 3 . V A b s o lu t e a b u n d a n c e a n d s p e c ie s c o m p o s it io n o f

C ic a d e l l id a e f e e d in g on H o lc u s a n d A g r o s t i s s p p 1 4 1

4 . 3 . v i C o m p a r is o n o f a b s o lu t e a b u n d a n c e o f p h lo e m a n d

m e s o p h y l l - f e e d i n g C ic a d e l l id a e

1 4 1

4 . 4 D is c u s s io n 1 4 4

C H A P T E R 5: V e g e ta t io n S t r u c t u r e a n d th e I n s e c t C o m m u n ity 1 4 9

5.1 I n t r o d u c t io n 1 4 9

5 .2 M e th o d s 1 5 3

5 .3 R e s u lt s1 5 3

5 . 3 . i V e g e ta t io n s t r u c t u r e a n d small s c a le v a r ia t io n in

h e r b i v o r e a b u n d a n c e a n d s p e c ie s r i c h n e s s

1 5 3

5 . 3 . i i V a r ia t io n in a b s o lu t e a b u n d a n c e o f s p e c ie s

b e tw e e n d i f f e r e n t s e r a i s ta g e s

1 5 8

5 . 3 . i i i

5 . 3 . iv

5 .4

V a r ia t io n in o v e r w i n t e r i n g s t r a t e g ie s a n d s p e c ie s

r i c h n e s s

V a r ia t io n in a b s o lu t e a b u n d a n c e o f b i r c h

h e r b i v o r e s a s s o c ia te d w ith th e u p p e r a n d low er

c a n o p y

D is c u s s io n

168

168

178

C H A P T E R 6 :

6.16.2

6 . 2 . i6 . 2 . i i

6.2.11. a

6 . 2 .11. b

6 . 2 . i i . c

6 . 2 . iii

6 . 2 . i i i . a

6 . 2 . i i i . b

6 .3

6 . 3 . 1

6 . 3 . i i

6 . 3 . i i . a

6 . 3 . i i . b

6 . 3 . iii

6 .4

6 . 4 . 1

6 . 4 . ii

6 . 4 . iii

V a r ia t io n in F o o d Q u a l i t y a n d P e r fo r m a n c e o f 182E r a n n i s d e f o l ia r ia ( L e p i d o p t e r a : G e o m e tr id a e )

I n t r o d u c t io n

E x p e r im e n t 1 : T h e e f f e c t o f le a f a g e on th e 184p e r f o r m a n c e o f E r a n n i s d e f o l ia r ia

A im s

M a te r ia ls a n d m e th o d s

T h e o r g a n is m s

S a m p l in g a n d e x p e r im e n t a l p r o c e d u r e

M o th s

B i r c h

M e a s u r e m e n t o f fo o d q u a l i t y

W ater c o n t e n t

T o u g h n e s s

N i t r o g e n a n d t a n n in c o n t e n t

N i t r o g e n c o n t e n t

T a n n i n c o n t e n t

R e s u lt s

M o th s

F o o d q u a l i t y

E x p e r im e n t 2 : T h e e f f e c t o f th e f r e e z in g o f

B . p e n d u l a le a v e s on la r v a l g r o w t h

A im s

M a te r ia ls a n d m e th o d s

M o th s

Fo od

R e s u lt s

E x p e r im e n t 3: I n v e s t ig a t io n o f th e e a r l y s p r i n g

p h e n o l o g y o f E^ d e f o l ia r ia

184184

184185

185

187187

197

197

197197197197198

A im s

M e th o d s

R e s u lt s

198

198198

6 .5 E x p e r i m e n t 4: T h e e f f e c t o f le a f t o u g h n e s s on 200s u r v i v a l o f e a r l y in s t a r la rv a e

6 . 5 . i A im s 2006 . 5 . i i M a t e r ia ls a n d m e th o d s 2026 .5 . i i i R e s u l t s 2026 . 6 D is c u s s i o n 2086 .7 C o n c l u s i o n 209

C H A P T E R 7: G e n e r a l D is c u s s i o n 210

A c k n o w le d g e m e n t s 214

B i b l i o g r a p h y 215

A p p e n d i c e s 232

S U M M A R Y

1. T h e th e s is a im s to t e s t L a w to n S M c N e i l l ' s (1979) h y p o t h e s i s

th a t th e a b s o lu t e a b u n d a n c e o f h e r b i v o r o u s in s e c t s

( e x p r e s s e d as n u m b e r / l e a f a re a o f h o s t p l a n t ) , a s s o c ia te d

w ith p la n t s o f e a r l y s u c c e s s i o n , is g r e a t e r th a n th a t o f

h e r b i v o r e s a s s o c ia t e d w ith la te s u c c e s s io n a l p l a n t s .

2 . T h e p r e d ic t e d d i f f e r e n c e s in a b s o lu t e a b u n d a n c e is re la te d

to th e postulated differences in the chemical defences of e a r ly a n d la te s u c c e s s io n a l p l a n t s , b e in g d e f e n d e d b y

q u a l i t a t i v e a n d q u a n t i t a t i v e d e f e n c e s r e s p e c t i v e l y .

3 . T h e h y p o t h e s i s w as te s te d f o r h e r b i v o r o u s H e m ip te r a a n d

C o le o p t e r a d u r i n g 1985 a n d 1986 o v e r an e x p e r im e n t a l

s u c c e s s io n a l g r a d i e n t a t S i lw o o d P a r k , B e r k s h i r e U . K . ,

s p a n n i n g f ro m v e r y e a r l y c o lo n is a t io n o f b a r e g r o u n d ,

t h r o u g h m a t u r e p a s t u r e to a b i r c h w o o d la n d .

4 . T h e h y p o t h e s i s w a s f o u n d to be t r u e . D i f f e r e n c e s in

a b s o lu te a b u n d a n c e b e tw e e n s e r a i s ta g e s d o m in a te d b y

h e r b s a n d g r a s s e s is m ost l i k e l y d u e to v a r ia t io n in f a c t o r s

o t h e r th a n t h a t in c h e m ic a l d e f e n c e s , eg p r e d a t io n o r

n u t r i e n t a v a i l a b i l i t y .

5 . Sm all s c a le v a r i a t i o n in s e v e r a l c o m m u n ity a t t r ib u te s . , w as

c o r r e la t e d w ith th e a b u n d a n c e a n d s p e c ie s r i c h n e s s o f

h e r b i v o r e s . C u r c u l i o n o i d e a a n d A u c h e n o r r h y n c h a d i f f e r e d

in t h e i r r e s p o n s e to sm all s c a le v a r ia t i o n . H o s t p la n t le a f

a re a a n d s t r u c t u r e w e r e im p o r t a n t f o r some s p e c i e s .

6 . E x a m in a t io n o f p a t t e r n s o f a b u n d a n c e a n d d i v e r s i t y o f

h e r b i v o r o u s i n s e c t s a n d p la n t s r e v e a le d th a t d i v e r s i t y o f

p la n t s is g r e a t e s t in e a r l y m id s u c c e s s io n a n d in s e c t s in

e a r ly s u c c e s s i o n . S p e c ie s r i c h n e s s a n d a b u n d a n c e o f

in s e c t s w e re c o m p a r a b le b e tw e e n y e a r s .

2

7. E x p e r i m e n t s u n d e r c o n t r o l l e d c o n d i t io n s e x a m in e d th e e f f e c t

o f food q u a l i t y on th e p e r f o r m a n c e o f E r a n n i s d e f o l ia r ia

( L e p i d o p t e r a : G e o m e t r i d a e ) . T h e d e v e lo p m e n t time a n d

p u p a l w e ig h t o f l a r v a e fe d y o u n g a n d o ld b i r c h le a v e s w e r e

c o m p a r e d . L a r v a e fe d on o ld e r le a v e s g e n e r a l l y p e r f o r m e d

b e t t e r . T h e s e r e s u l t s a r e c o n t r a r y to c u r r e n t t h e o r y , a n d

a r e d i s c u s s e d in th e l i g h t o f c u r r e n t p l a n t / h e r b i v o r e

t h e o r y .

3

L I S T O F T A B L E S

2.1 A g e a n d n o m e n c la t u r e o f s e r a i s ta g e s

2 . 2 M ode l a n a l y s i s o f d e v i a n c e ta b le f o r tw o -w a y a n a ly s i s

o f d e v i a n c e ( A N O D E V ) ( ta k e n from M c C u l la g h &

N e l d e r , 1985).

3 .1 S o r e n s o n s I n d e x o f S i m i l a r i t y f o r p la n t s p e c ie s in e a c h

m ajor p la n t fa m ily b e t w e e n in d i f f e r e n t s e r a i s t a g e s .

3 .2 P r o p o r t io n o f le a f a r e a p r o v i d e d b y th e d o m in a n t

s p e c ie s to th e c o m m u n it y a n d m ajor p la n t fam il ie s o n

e a c h d a t e , (a) r u d e r a l 1985, (b ) r u d e r a l 1986,

(c) e a r l y 1985, ( d ) e a r l y 1986, (e) e a r ly mid 1985 , ( f)

e a r l y m id 1986, ( g ) la te m id 1985, (h) late m id 1986,

a n d s p e c ie s r i c h n e s s o f e a c h p la n t fa m ily a n d

c o m m u n it y .

3 .3 T o t a l , a d u l t a n d n y m p h a l a b u n d a n c e o f e a c h m ajo r

i n s e c t g r o u p on s i t e s o f d i f f e r e n t s u c c e s s io n a l a g e o v e r

two y e a r s (* = s i g n i f i c a n t a t P < 0 . 0 5 ) .

3 . 4 S o r e n s o n s I n d e x o f S i m i l a r i t y f o r s p e c ie s in e a c h m ajor

in s e c t g r o u p b e tw e e n y e a r s on s e r a i s t a g e s o f th e sam e

a g e .

3 .5 S o r e n s o n s In d e x o f S i m i l a r i t y f o r s p e c ie s in e a c h m ajor

in s e c t g r o u p b e t w e e n s e r a i s t a g e s o f d i f f e r e n t

s u c c e s s io n a l a g e . D a ta su m m e d o v e r two y e a r s .

3 . 6 S p e c ie s r i c h n e s s o f e a c h in s e c t g r o u p on lo w e r a n d

u p p e r c a n o p y 1985 a n d lo w e r c a n o p y 1986 in m o n th ly

s a m p le s .

3 .7 A b u n d a n c e a n d p r o p o r t i o n o f to ta l a b u n d a n c e on

O n c o p s is ( C i c a d e l l i d a : H e m ip t e r a ) in e a c h s p e c ie s on

t h r e e d a t e s in u p p e r a n d lo w e r c a n o p y 1985 a n d lo w er

c a n o p y 1986.

4

4.1 M ean a b s o lu t e a b u n d a n c e a n d s t a n d a r d e r r o r s o f

C u r c u l io n o id e a b y h o s t p la n t fa m ily a n d s p e c ie s fe e d in g

on w o o d y a n d n o n - w o o d y p l a n t s . a b h f , 9 ) ~1 5 0 .2 6 , P < 0 . 0 0 1 ) ; a b h s , F (1 2g2) = 4 3 0 .9 7 , P <

0 . 0 0 1 .

4 .2

4 .3

M ea n a b s o lu t e a b u n d a n c e a n d s t a n d a r d e r r o r s o f

C u r c u l i o n o i d e a b y h o s t p la n t fa m i ly a n d s p e c ie s f e e d in g

o n w o o d y a n d n o n - w o o d y p la n t s on e a c h d a t e . D ata

p o o le d o v e r two y e a r s , ( a b h f , d a t e F , „ = 4 4 .0 4 ,

P < 0 .0 0 1 , d a t a . p l a n t F

a b h s , d a t e F

F

( 4 ,3 9 4 )

f 4 3941

= 1 .5 0 0 6 , P > 0 .0 5 ;

(4 ,2 8 2 )

(4 ,2 8 2 )= 1 .5 0 6 , P > 0 .0 5 .

= 5 3 .2 3 , P < 0 .0 0 1 , d a t e . p l a n t

M ean a b s o lu t e a b u n d a n c e a n d s t a n d a r d e r r o r s o f

C u r c u l i o n o i d e a b y (a) h o s t p la n t f a m i ly , (b) h o s t p la n t

s p e c ie s on m ajor p la n t fa m i l ie s in d i f f e r e n t s e r a i s t a g e s .

S e e t e x t f o r s i g n i f i c a n c e l e v e l s .

4 .4 M ea n a b s o lu t e a b u n d a n c e o f H e t e r o p t e r a b y (a) h o s t

p la n t f a m i ly , (b ) h o s t p l a n t s p e c ie s on m ajor p la n t

fa m il ie s in d i f f e r e n t s e r a i s t a g e s . D i f f e r e n c e s b e tw e e n

p la n t fa m il ie s a n d s e r a i s t a g e s te s te d b y

K r u s k a l l - W a l l i s o n e w a y A N O V A .

4 .5 A d u l t a b u n d a n c e o f C i c a d e l l i d a e s p e c i a l i s i n g o n

(a) A g r o s t i s s p p , (b ) H o lc u s s p p in d i f f e r e n t s e r a i

s t a g e s .

5 .1 S p e a r m a n 's R a n k C o r r e l a t i o n C o e f f i c ie n t s f o r a d u l t

a b u n d a n c e o f com m on h e r b i v o r e s p e c ie s in s u b p lo t s

w ith s e v e r a l m e a s u r e d v e g e t a t io n a t t r ib u t e s d u r i n g

A u g u s t 1985 in (a) r u d e r a l , (b ) e a r l y s u c c e s s i o n ,

(c) e a r l y m i d s u c c e s s i o n , (d ) late s u c c e s s i o n .

* P < 0 .0 5 , ** P < 0 . 0 1 , *** P < 0 .0 0 1 .

5 .2 P e a r s o n 's C o r r e l a t io n C o e f f i c i e n t f o r s p e c ie s r i c h n e s s

o f H e t e r o p t e r a , C u r c u l i o n o i d e a , C ic a d e l l id a e a n d

D e lp h a c id a e in s u b p l o t s w ith s e v e r a l m e a s u r e d

v e g e t a t io n a t t r i b u t e s d u r i n g A u g u s t 1985 in r u d e r a l ,

e a r l y s u c c e s s i o n , e a r l y m id s u c c e s s io n a n d late

s u c c e s s i o n . * P < 0 . 0 5 , ** P < 0 . 0 1 , *** P < 0 .0 0 1 .

5 .3

5

C o r r e l a t io n c o e f f i c i e n t f o r a u t o c o r r e la t io n b e tw e e n

v e g e t a t io n a t t r i b u t e s f o r h o s t p la n t s in s u b p lo t s d u r i n g

A u g u s t 1985. S e p a r a t e ta b le s f o r th e h o s t p la n t o f

h e r v i b o r e s in e a c h s e r a i s t a g e ; (a) T r i f o l iu m p r a t e n s e

o n r u d e r a l s i t e ; (b ) T r i f o l i u m p r a t e n s e a n d T r i f o l i u m

s p p ( in p a r e n t h e s i s ) in e a r l y s u c c e s s io n ; (c) T r i f o l i u m

p r a t e n s e a n d T r i f o l i u m s p p ( in p a r e n t h e s i s ) in e a r l y

m id s u c c e s s io n ; (d ) A g r o s t i s c a p i l l a r i s a n d H o lc u s

la n a t u s ( in p a r e n t h e s i s ) on r u d e r a l s i t e ; (e) g r a s s e s

in e a r l y s u c c e s s i o n ; ( f ) H o lc u s la n a t u s in e a r l y

m id s u c c e s s io n ; (g ) H o lc u s la n a tu s a n d D a c t y l i s

g lo m e r a ta ( in p a r e n t h e s i s ) in late m id s u c c e s s io n ;

(h ) S p e r g u l a a r v e n s i s on r u d e r a l s i t e ;

( i) T r i p l e u r o s p e r m u m in o d o r u m in e a r l y s u c c e s s io n ; (j)

C i r s i u m a r v e n s e in la te m id s u c c e s s io n . * P < 0 .0 5 , **

P < 0 .0 1 , *** P < 0 .0 0 1 .

5 .4 P e a r s o n 's C o r r e l a t i o n C o e f f i c i e n t f o r s p e c ie s r i c h n e s s

o f H e t e r o p t e r a , C u r c u l i o n o i d e a , C i c a d e l l id a e a n d

D e lp h a c id a e w ith t h a t o f th e o t h e r in s e c t g r o u p s

d u r i n g A u g u s t 1985, in r u d e r a l , e a r l y , e a r l y m id a n d

la te m id s u c c e s s io n . * P < 0 .0 5 , ** P < 0 .0 1 , *** P <

0 .001.

6 . 1 S u r v i v a l o f E . d e f o l ia r ia la r v a e on d ie t s o f y o u n g

j3. p e n d u la le a v e s ( t r e a t m e n t) a n d n o r m a l ly a g in g

le a v e s ( c o n t r o l ) . A s t e r i s k s r e p r e s e n t le v e l o f

s i g n i f i c a n c e , ** P < 0 . 0 1 , *** P < 0 .0 0 1 ) .

6 .2 S u r i v a l o f E . d e f o l ia r ia la r v a e on d ie t s o f f r e s h

_B. p e n d u la le a v e s ( c o n t r o l ) a n d on le a v e s f r o z e n f o r

24 h o u r s p r i o r to l a r v a l fe e d in g ( t r e a t m e n t ) . ( N . S . =

n o t s i g n i f i c a n t l y d i f f e r e n t , P = 0 . 2 9 ) .

6 .3 P u p a l w e ig h t (m g) a n d la r v a l d e v e lo p m e n t ra t e

( i n v e r s e o f d a y s f r o m h a t c h i n g to p u p a t io n ) o f

E . d e fo l ia r ia fe d f r e s h ]3. p e n d u la le a v e s

( c o n t r o l) a n d le a v e s w h ic h h a d b e e n f r o z e n f o r 24

h o u r s ( t r e a t m e n t ) . (M ean ± 1 S . E . , N = 30,

N . S . = n o t s i g n i f i c a n t l y d i f f e r e n t . )

6 .4

6

C o m p a r is o n o f t o u g h n e s s o f y o u n g B_. p e n d u la le a v e s

w ith t h a t o f m a t u r e le a v e s (mean ± 1 . S . E . )

7

L I S T O F F I G U R E S

3.1 N u m b e r o f p l a n t s p e c ie s r e c o r d e d in e a ch o f two y e a r s

on r u d e r a l ( R ) , e a r l y ( E ) , e a r ly mid (E M S ) a n d late

m id ( L M S ) s u c c e s s i o n a l s i t e s .

3 .2 N u m b e r o f p l a n t s p e c i e s r e c o r d e d on f o u r s e r a i s t a g e s

b y su m m in g tw o s i t e s o f th e sam e a g e ( r u d e r a l ( R ) ,

e a r l y ( E ) , e a r l y m id ( E M S ) , late m id ( L M S ) ) .

3 .3 N u m b e r o f p l a n t s p e c i e s r e c o r d e d in e a c h o f th e m ajor

p la n t fa m il ie s d u r i n g 1985 a n d 1986 on s i te s o f

d i f f e r e n t s u c c e s s i o n a l a g e , ( (a ) r u d e r a l , (b ) e a r l y ,

(c) e a r ly m i d , (d ) late m id s u c c e s s io n ; m f = m in o r

fa m il ie s ; Le g = L e g u m in o s a e , C o = C o m p o s i t a e , C r =

C r u c i f e r a e , Po = P o ly g o n a c e a e , G r = G r a m in e a e ) .

3 .4 N u m b e r o f p l a n t s p e c i e s r e c o r d e d on e a c h d a t e d u r i n g

1985 a n d 1986 on s i t e s o f d i f f e r e n t s u c c e s s io n a l a g e

( (a ) r u d e r a l , ( b ) e a r l y , (c) e a r l y m id , (d ) la te

m i d s u c c e s s i o n ) .

3 .5 T o t a l le a f a r e a o n s e r a i s t a g e s o f d i f f e r e n t s u c c e s s io n a l

a g e , d a ta s u m m e d o v e r tw o y e a r s ( R = r u d e r a l , E =

e a r l y , E M S = e a r l y m id , L M S = late m id , L = la te

s u c c e s s i o n ) .

3 .6 L e a f a re a r e c o r d e d on s i te s o f d i f f e r e n t s u c c e s s io n a l

a g e a t m o n t h ly in t e r v a l s o v e r two y e a r s .

3 .7 M ean le a f a r e a p e r b a g a t m o n th ly in t e r v a l s on u p p e r

a n d lo w e r c a n o p y b i r c h 1985 a n d lo w e r c a n o p y b i r c h

1986.

3 .8 L e a f a re a o f (a) L e g u m in o s a e , (b ) C o m p o s i t a e , (c)

C r u c i f e r a e , ( d ) P o ly g o n a c e a e , (e) G r a m in a e , ( f) m in o r

fa m il ie s on s e r a i s t a g e s o f d i f f e r e n t s u c c e s s io n a l a g e s .

D ata p o o le d o v e r tw o y e a r s . ( R = r u d e r a l , E = e a r l y ,

E M S = e a r l y m i d s u c c e s s i o n , L M S = late m i d s u c c e s s i o n ) .

8

3 .9 P r o p o r t io n o f to ta l le a f a re a p r o v i d e d b y m ajor p la n t

fa m il ie s on s e r a i s t a g e s o f d i f f e r e n t s u c c e s s io n a l a g e .

(a) r u d e r a l 1 985 , ( b ) r u d e r a l 1986, (c) e a r ly 1985 ,

(d ) e a r l y 1986, (e) e a r l y mid 1985, ( f) e a r ly mid 1986,

(g ) late mid 1985, (h ) late m id s u c c e s s io n 1986.

3 .1 0 T o t a l n u m b e r o f (a) in s e c t h e r b i v o r e in d i v i d u a l s (b )

a d u l t in s e c t h e r b i v o r e s ( e x c lu d in g A p h i d i d a e ,

C o c c o id e e , A le y ro cW » A e a (H e m ip te ra \ T h y s a r p p te r a a n d

L e p i d o p t e r a ) on s e r a i s t a g e s o f d i f f e r e n t s u c c e s s io n a l

a g e . D ata su m m ed o v e r two y e a r s ( R = r u d e r a l , E =

e a r l y , E M S = e a r l y m id , L M S = late m id s u c c e s s io n , L =

l a t e ) .

3.11 T o t a l n u m b e r o f i n d i v i d u a l s in e a c h m ajor in s e c t g r o u p

on s e r a i s t a g e s o f d i f f e r e n t s u c c e s s io n a l a g e . D a ta

p o o le d o v e r tw o y e a r s ( R = r u d e r a l , E = e a r l y , E M S =

e a r l y m id , L M S = la te m id , L = late s u c c e s s i o n ) .

3 .1 2 T o t a l n u m b e r o f a d u l t s in e a c h m ajor in s e c t g r o u p on

s e r a i s t a g e s o f d i f f e r e n t s u c c e s s io n a l a g e . D ata p o o le d

o v e r tw o y e a r s ( R = r u d e r a l , E = e a r l y , E M S = e a r l y

m id , L M S = la te m id , L = late s u c c e s s i o n ) .

3 .1 3 T o t a l n u m b e r o f i n s e c t h e r b i v o r e in d i v i d u a l s ( e x c lu d in g

A p h i d i d a e , C o c c o i d a e , , A l e y r o & d i A e a (H em iptera),

T h y s a n o p t e r a a n d L e p i d o p t e r a ) r e c o r d e d on m o n th ly

s a m p le s o v e r tw o y e a r s on s e r a i s t a g e s o f d i f f e r e n t

s u c c e s s io n a l a g e .

3 .1 4 T o t a l n u m b e r o f a d u l t h e r b i v o r e s ( e x c lu d in g

A p h i d i d a e , C o c c o id ^ a i , A le y r o A o \ d e a (Hemiptera'),

T h y s a n o p t e r a a n d L e p i d o p t e r a ) r e c o r d e d on m o n t h ly

s a m p le s o v e r tw o y e a r s on s e r a i s t a g e s o f d i f f e r e n t

s u c c e s s io n a l a g e .

9

3 .1 5 M ean n u m b e r o f in s e c t h e r b i v o r e s p e c ie s ( e x c lu d in g

A p h i d i d a e , C o cco id e a . , A l e y r o ^ o i d e a (H e m ip te ra \

T h y s a n a p t e r a a n d L e p i d o p t e r a ) on s e r a i s t a g e s o f

d i f f e r e n t s u c c e s s io n a l a g e (a) d a ta sum m ed o v e r two

y e a r s , (b ) f o r e a c h y e a r ( R = r u d e r a l , E = e a r l y , E M S

= e a r l y m id , L M S = late m id , L = late s u c c e s s i o n ) .

B a r s a r e s t a n d a r d e r r o r s . C le a r = 1985, h a t c h e d =

1986.

3 .1 6 N u m b e r o f in s e c t h e r b i v o r e s p e c ie s ( e x c lu d in g

A p h i d i d a e , C o c c o i d e a , Aleyro<Va>dee. (H e m ip te ra \

T h y s a n o p t e r a a n d L e p i d o p t e r a ) in m o n th ly s a m p le s

o v e r tw o y e a r s on s e r a i s t a g e s o f d i f f e r e n t

s u c c e s s io n a i a g e .

3 .1 7 N u m b e r o f s p e c i e s in e a c h m ajor in s e c t g r o u p d u r i n g

tw o y e a r s on s e r a i s t a g e s o f d i f f e r e n t s u c c e s s io n a l a g e

( H e t = H e t e r o p t e r a , P s y = P s y l l id a e , C e r e =

C e r c o p i d a e , D e l = D e lp h a c id a e , C i c = C i c a d e l l i d a e ,

C u r e = C u r c u l i o n o i d e a , C h r y = C h r y s o m e l i d a e ) .

3 .1 8 H o s t p la n t fa m i ly o f s p e c i e s in e a c h m ajor in s e c t g r o u p

a n d su m m ed o v e r a l l g r o u p s ( G e n = g e n e r a l i s t , L e g =

L e g u m in o s a e , C o = C o m p o s i t a e , C r = C r u c i f e r a e , P =

P o ly g o n a c e a e , G r = G r a m in e a e , P P = p a r t ia l p r e d a t o r ,

B = b i r c h , m f = m in o r f a m i l ie s ) . S h a d e d c o lu m n s on

C ic a d e l l id a e in d ic a t e T y p h l o c y b i n a e . H a t c h e d c o lu m n s

on (h ) in d i c a t e c h e w in g in s e c t s .

3 .1 9 P r o p o r t io n o f a d u l t s in e a c h m ajor in s e c t g r o u p on

u p p e r a n d lo w e r c a n o p y b i r c h 1985 a n d low er c a n o p y

1986.

4 .1 M ean a b s o lu t e a b u n d a n c e o f C ic a d e l l id a e b y (a) h o s t

p la n t f a m i ly , (b ) h o s t p la n t s p e c i e s in d i f f e r e n t s e r a i

s t a g e s ( R = r u d e r a l , E = e a r l y s u c c e s s i o n , E M S = e a r l y

m i d s u c c e s s i o n , L M S = la te m id s u c c e s s io n , L = la te

s u c c e s s i o n ) . B a r s a r e s t a n d a r d e r r o r s .

10

4 .2 M ean a b s o lu t e a b u n d a n c e o f C i c a d e l l id a e b y (a) h o s t

p la n t f a m i ly , (b) h o s t p la n t s p e c i e s from M a y to

S e p t e m b e r in d i f f e r e n t s e r a i s t a g e s ( R = r u d e r a l , E =

e a r ly s u c c e s s i o n , E M S = e a r ly m i d s u c c e s s i o n , L M S =

la te m i d s u c c e s s i o n , L = late s u c c e s s i o n ) . B a r s a r e

s t a n d a r d e r r o r s .

4 .3 M ean a b s o lu t e a b u n d a n c e o f D e lp h a c id a e b y (a) h o s t

p la n t f a m i ly , (b ) h o s t p la n t s p e c ie s in d i f f e r e n t s e r a i

s t a g e s ( R = r u d e r a l , E = e a r ly s u c c e s s i o n , E M S = e a r l y

m i d s u c c e s s i o n , L M S = late m i d s u c c e s s i o n ) . B a r s a r e

s t a n d a r d e r r o r s .

4 .4 M ean a b s o lu t e a b u n d a n c e o f D e lp h a c id a e b y (a) h o s t

p la n t fa m ily (b ) h o s t p la n t s p e c i e s fro m M a y to

S e p t e m b e r in d i f f e r e n t s e r a i s t a g e s ( R = r u d e r a l , E =

e a r l y s u c c e s s i o n , E M S = e a r ly m i d s u c c e s s i o n , L M S =

late m i d s u c c e s s i o n ) . B a r s a r e s t a n d a r d e r r o r s .

4 .5 M ean a b s o lu t e a b u n d a n c e o f C u r c u l i o n o i d e a b y (a) h o s t

p la n t f a m i ly , ( b ) h o s t p la n t s p e c ie s in d i f f e r e n t s e r a i

s t a g e s ( R = r u d e r a l , E = e a r ly s u c c e s s i o n , E M S = e a r l y

m i d s u c c e s s i o n , L M S = late m i d s u c c e s s i o n , L = late

s u c c e s s i o n ) . B a r s a r e s t a n d a r d e r r o r s .

4 .6 M ean a b s o lu t e a b u n d a n c e o f C u r c u l io n o id e a b y (a) h o s t

p la n t f a m i ly , (b ) h o s t p la n t s p e c i e s from M a y to

S e p t e m b e r in d i f f e r e n t s e r a i s t a g e s ( R = r u d e r a l , E =

e a r l y s u c c e s s i o n , E M S = e a r ly m i d s u c c e s s i o n , L M S =

late m i d s u c c e s s i o n , L = late s u c c e s s i o n ) . B a r s a r e

s t a n d a r d e r r o r s .

4 .7 M ean a b s o lu t e a b u n d a n c e o f H e t e r o p t e r a b y (a) h o s t

p la n t f a m i ly , (b ) h o s t p la n t s p e c ie s in d i f f e r e n t s e r a i

s t a g e s ( a b h f , K r u s k a l l - W all is = 4 5 .6 0 2 , n = 342, P <

0.0001 ; a b h s , K r u s k a l l - W a l l i s = 7 9 .5 2 2 , n = 167, P <

0 .0 0 1 ) ( R = r u d e r a l , E = e a r l y s u c c e s s i o n , E M S = e a r l y

m i d s u c c e s s i o n , L M S = late m i d s u c c e s s i o n , L = la te

s u c c e s s i o n ) .

11

M ean a b s o lu t e a b u n d a n c e o f H e t e r o p t e r a b y (a) h o s t

p la n t f a m i ly , (b) h o s t p la n t s p e c ie s from M a y to

S e p t e m b e r in d i f f e r e n t s e r a i s ta g e s ( a b h f , M a y ,

K r u s k a l l - W a l l i s = 3 . 6 2 1 , n = 25, P = 0 .4 6 ; J u n e ,

K r u s k a l l - W a l l i s = 6 .9 1 8 , n = 37, P = 0 .1 4 ; J u l y ,

K r u s k a l l - W a l l i s = 1 6 .3 0 4 , n = 74, P < 0 . 0 1 ; A u g u s t ,

K r u s k a l l - W a l l i s = 3 0 .7 0 3 , n = 9 7 , P < 0 .0 0 0 1 ;

S e p t e m b e r , K r u s k a l l - W a l l i s = 1 .9 2 1 8 , n = 9 0 , P =

0.7501 ; a b h s , M a y , K r u s k a l l - W a l l i s = 2 .2 3 1 9 , n = 1 2 , P

= 0 .5 2 5 7 ; J u n e , K r u s k a l l - W a l l i s = 1 3 .0 4 7 , n = 2 2 , P <

0 .0 1 ; J u l y , K r u s k a l l - W allis = 23.651 , n = 3 9 , P <

0 . 0 0 0 1 ; A u g u s t , K r u s k a l l - W a l l i s = 3 6 .4 3 9 , n = 52 , P <

0 . 0 0 1 ) ; S e p t e m b e r , K r u s k a l l - W a l l i s = 1 1 .3 1 4 , n = 4 1 , P

< 0 .0 5 ) ( R = r u d e r a l , E = e a r ly s u c c e s s i o n , E M S =

e a r l y m i d s u c c e s s i o n , L M S = late m id s u c c e s s io n , L = late

s u c c e s s i o n ) .

4 .9 M ean a b s o lu t e a b u n d a n c e o f C h r y s o m e l id a e b y (a) h o s t

p la n t f a m i ly , (b ) h o s t p la n t s p e c ie s in d i f f e r e n t s e r a i

s t a g e s ( R = r u d e r a l , E = e a r l y s u c c e s s i o n , E M S = e a r l y

m i d s u c c e s s i o n , L M S = late m id s u c c e s s i o n ) . ( a b h f ,

K r u s k a l l - W a l l i s = 9 .6 8 9 4 , n = 58 , P < 0 .0 5 ; a b h s ,

K r u s k a l l - W a l l i s = 1 2 .4 6 , n = 2 3 , P < 0 . 0 0 1 ) .

4 .1 0 M ea n a b s o lu t e a b u n d a n c e o f P s y l l id a e b y (a) h o s t p la n t

f a m i ly , (b ) h o s t p l a n t s p e c ie s in d i f f e r e n t s e r a i s t a g e s

( R = r u d e r a l , E = e a r l y s u c c e s s i o n , E M S = e a r l y

m i d s u c c e s s i o n , L M S = late m id s u c c e s s io n , L = la te

s u c c e s s i o n ) , ( a b h f , K r u s k a l l - W a l l i s = 2 4 .9 2 9 6 , n = 3 8 ,

P < 0 . 0 0 0 1 ; a b h s , K r u s k a l l - W a l l i s = 2 5 .7 9 4 , n = 4 8 , P

< 0 . 0001) .

4.11 M ean a b s o lu t e a b u n d a n c e o f C e r c o p id a e b y (a) h o s t

p la n t f a m i ly , (b ) h o s t p la n t s p e c ie s in d i f f e r e n t s e r a i

s t a g e s ( R = r u d e r a l , E = e a r l y s u c c e s s i o n , E M S = e a r l y

m i d s u c c e s s i o n , L M S = la te m i d s u c c e s s i o n , L = la te

s u c c e s s i o n ) , ( a b h f , K r u s k a l l - W a l l i s = 3 .6 2 7 6 , n = 2 0 ,

P = 0 .4 5 8 7 ; a b h s , K r u s k a l l - W a l l i s = 11 .2561 , n = 2 0 , P

= 0 .0 2 3 8 ) .

12

4 .1 2 M ean a b s o lu t e a b u n d a n c e o f C i c a d e l l id a e , H e t e r o p t e r a

a n d P s y l l id a e b y h o s t p la n t fa m ily a n d h o s t p la n t

s p e c ie s f e e d in g on w o o d y a n d n o n - w o o d y p l a n t s . B a r s

on (a) a n d ( b ) a r e s t a n d a r d e r r o r s . H e t e r o p t e r a ,

a b h f , K r u s k a l l - W a l l is = 2 6 .6 7 8 , n = 308, P < 0 . 0 0 0 1 ;

a b h s , K r u s k a l l - W a l l i s = 71 .5 5 8 , n = 166, P < 0 . 0 0 0 1 .

P s y l l i d a e , a b h f , K r u s k a l l - W a l l i s = 3 1 .0 9 6 , n = 57, P <

0 . 0 0 1 ; a b h s , K r u s k a l l - W a l l i s = 2 4 .7 8 3 , n = 4 8 , P <

0 . 0 0 0 1 .

4 .1 3 M ean a b s o lu t e a b u n d a n c e o f C ic a d e l l id a e b y (a) h o s t

p la n t f a m i ly , (b ) h o s t p la n t s p e c ie s f e e d in g on w o o d y

a n d n o n -v v o o d y p la n t s fro m M ay to S e p t e m b e r . B a r s

a r e s t a n d a r d e r r o r s . ( a b h f , 9 4 ) = 1 9 .3 3 , P <

0 .0 0 1 ; a b h s , Fflt = 1 2 .2 4 , P < '0 .0 0 1 ) .(.4,1 /b J

4 .1 4 M ean a b s o lu t e a b u n d a n c e o f H e t e r o p t e r a b y (a) h o s t

p la n t f a m i ly , (b ) h o s t p la n t s p e c ie s f e e d in g on w o o d y

a n d n o n - w o o d y p l a n t s ( h a t c h e d b a r s = w o o d y p l a n t s ,

c l e a r b a r s = n o n - w o o d y p la n t s ) ( a b h f , M a y ,

K r u s k a l l - W a l l i s = 0 .4 8 7 5 , n = 2 4 , P = 0 .4 8 5 1 ; J u n e ,

K r u s k a l l - W a l l i s = 2 .4 2 1 7 , n = 3 5 , P = 0 .1 1 9 7 ; J u l y ,

K r u s k a l l - W a l l i s = 7 . 4 4 3 , n = 7 4 , P < 0 .0 1 ; A u g u s t ,

K r u s k a l l - W a l l i s = 2 4 .8 3 9 , n = 1 0 0 , P < 0 . 0 0 1 ;

S e p t e m b e r , K r u s k a l l - W a l l i s = 0 .2 0 2 6 , n = 8 8 , P =

0 .6 5 9 2 ; a b h s , M a y , K r u s k a l l - W a l l i s = 0 .7 2 0 0 , n = 14,

P = 0.3961 ; J u n e , K r u s k a l l - W a l l i s = 7 .0 3 1 , n = 2 5 , P <

0 . 0 1 ; J u l y , K r u s k a l l - W a ll is = 1 4 .9 8 6 , n = 4 2 , P <

0.0001 ; A u g u s t , K r u s k a l l - W a l l i s = 2 8 .3 0 9 , n = 5 5 , P <

0 .0 0 1 ) ; S e p t e m b e r , K r u s k a l l - W a l l i s = 6 .0 7 9 , n = 4 3 , P

< 0 . 0 5 ) .

4 .1 5 M ea n a b s o lu t e a b u n d a n c e o f P s y l l id a e b y (a) h o s t p la n t

fa m ily a n d ( b ) h o s t p l a n t s p e c ie s f e e d in g on w o o d y

a n d n o n - w o o d y p l a n t s . I n s u f f i c ie n t d a ta to a llow

s t a t is t ic a l c o m p a r i s o n s .

13

4 .1 6 M e a n a b s o lu t e a b u n d a n c e o f C u r c u l io n o id e a b y (a) h o s t

p l a n t f a m i ly , (b ) h o s t p la n t s p e c ie s on m ajor p la n t

fa m il ie s (d a ta p o o le d o v e r all d a t e s a n d all s e r a i

s t a g e s ) ( L = L e g u m i n o s a e , C o = C o m p o s i t a e , C r =

C r u c i f e r a e , Po = P o ly g o n a c e a e , B = b i r c h ) . B a r s a r e

s t a n d a r d e r r o r s .

4 .1 7 M ea n a b s o lu t e a b u n d a n c e o f H e t e r o p t e r a b y (a) h o s t

p l a n t f a m i ly , (b ) h o s t p la n t s p e c ie s on m ajor p la n t

fa m il ie s (d a ta p o o le d o v e r all d a t e s a n d a ll s e r a i

s t a g e s ) ( L = L e g u m i n o s a e , C o = C o m p o s i t a e , C r =

C r u c i f e r a e , Po = P o ly g o n a c e a e , B = b i r c h , G r =

G r a m in e a e , M F = m in o r f a m i l ie s , G = g e n e r a l i s t ( s p e c ie s

a s s o c ia t e d w ith m o re t h a n o n e p la n t f a m i l y ) ) .

4 .1 8 M e a n a b s o lu t e a b u n d a n c e o f P s y l l id a e b y (a) h o s t p la n t

f a m i ly , (b ) h o s t p l a n t s p e c i e s on m ajor p la n t fa m il ie s

( L = L e g u m in o s a e , C o = C o m p o s i t a e , Po =

P o ly g o n a c e a e , M F = m in o r f a m i l ie s , B = b i r c h ) .

4 .1 9 M e a n a b s o lu t e a b u n d a n c e o f H e t e r o p t e r a b y (a) h o s t

p la n t f a m i ly , (b ) h o s t p la n t s p e c ie s on h e r b s , g r a s s

a n d b i r c h (d a ta p o o le d o v e r a ll d a t e s a n d s e r a i

s t a g e s ) .

4 .2 0 M e a n a b s o lu t e a b u n d a n c e o f C i c a d e l l id a e b y h o s t p la n t

s p e c i e s fe e d in g o n (a) A g r o s t i s a n d (b ) H o lc u s

( G r a m in e a e ) in d i f f e r e n t s e r a i s t a g e s ( R = r u d e r a l , E =

e a r l y s u c c e s s i o n , E M S = e a r ly m i d s u c c e s s i o n , L M S =

la te m i d s u c c e s s i o n ) . B a r s a r e s t a n d a r d e r r o r s .

4 .21 M ea n a b s o lu t e a b u n d a n c e b y (a) h o s t p la n t fa m ily o f

C ic a d e l l id a e e x c l u d i n g T y p h l o c y b i n a e (b ) h o s t p la n t

s p e c ie s o f C i c a d e l l i d a e e x c l u d i n g T y p h l o c y b i n a e (c)

h o s t p la n t fa m ily o f T y p h l o c y b i n a e a n d (d ) h o s t p la n t

s p e c ie s o f T y p h l o c y b i n a e in d i f f e r e n t s e r a i s ta g e s ( R =

r u d e r a l , E = e a r l y s u c c e s s i o n , E M S = e a r l y

m i d s u c c e s s i o n , L M S = la te m i d s u c c e s s i o n , L = la te

s u c c e s s i o n ) . B a r s a r e s t a n d a r d e r r o r s .

14

4 .2 2 M e a n a b s o lu t e a b u n d a n c e b y (a) h o s t p la n t fam ily o f

C ic a d e l l id a e e x c l u d i n g T y p h l o c y b i n a e , (b) h o s t p la n t

s p e c i e s o f C i c a d e l l i d a e e x c lu d in g T y p h l o c y b i n a e , (c)

h o s t p la n t f a m i ly o f T y p h l o c y b i n a e a n d (d ) h o s t p la n t

s p e c i e s o f T y p h l o c y b i n a e on w o o d y a n d n o n - w o o d y

p la n t s ( h a t c h e d c o lu m n s = w o o d y , c l e a r c o lu m n s =

n o n - w o o d y p l a n t s ) . B a r s a r e s t a n d a r d e r r o r s .

5.1 H o s t p la n t fa m i ly a n d a d u l t a b u n d a n c e o f a b u n d a n t

h e r b i v o r e s p e c i e s r e c o r d e d on th e f o u r y o u n g e r s e r a i

s t a g e s . D a ta p o o le d o v e r tw o y e a r s . (a) A p io n

a p r i c a n s F p = 8 . 9 3 , P < 0 .0 1 ; (b ) A p i o n a s s i m i le ,

F p = 9 .5 7 1 , P < 0 .0 1 ; (c) A p i o n a e t h i o p s , F p

= 2 1 .5 2 , P < 0 . 0 0 1 ; (d) S i to n a l i n e a t u s , F p =

4 .4 5 9 , P < 0 .0 5 ; (e) S i to n a h i s p i d u l u s , F ^ ^ = 2 .3 1 5 ,

P > 0 .0 5 ; ( f) S i to n a s u l c i f r o n s , F

0 .0 5 ; (g ) M a c r o s t e le s l a e v i s , F

0 . 0 0 1 ; (h ) R e c i l ia c o r o n i f e r a , F

( 3 ,3 )0 .2 3 6 , P >

6 2 .3 5 , P <( 3 ,8 )

= 4 . 4 3 , P > 0 .0 5 ;( 3 ,7 )

( i) A d a r r u s o c e l l a r i s , F p 13 = 11 .8 2 9 , P < 0 .0 1 ; (j)

P s a m m o te tt ix c o n f i n i s , F rr) = 1 2 .1 9 , P < 0 .0 1 ; ( k ) --------------------- ------------- 1 3 , DJ

E u s c e i i s i n c i s u s , F p

M o c y d io p s i s p a r v i c a u d a , F

= 4 1 .1 1 ,

( 3 ,1 1 )

p < 0 . 0 0 1 ; (I)

1 1 .0 7 , P < 0 . 0 1 ;

6 . 0 6 , P < 0 .0 5 ;

2 7 .8 6 , P < 0 .0 0 1 ;(n ) Z y g i n i d i a s c u t e l l a r i s , F p 12^

(o) J a v e s e l la p e l l u c i d a , F p = 8 .7 1 3 , P < 0 . 0 1 ; ( p )

D i c r a n o t r o p i s hama

P a r a la b q r n ia a a l e i , F

D i c r a n o t r o p i s h a m a ta , F fo 0 . = 2 .9 0 4 , P > 0 .0 5 ; (q )----------------------- ----------- 13,»J

( 3 ,8 )= 6 . 3 3 , P < 0 .0 5 . P <

0 . 0 5 , ** P < 0 . 0 1 , *** P < 0 .0 0 1 .

5 .2 M e a n a b s o lu t e a b u n d a n c e b y h o s t p la n t s p e c ie s o f

a b u n d a n t h e r b i v o r e s p e c ie s r e c o r d e d on th e f o u r

y o u n g e r s e r a i s t a g e s . D ata p o o le d o v e r two y e a r s ,

(a) A p i o n a s s i m i l e , F,

A p i o n a p r i c a n s , F

a e t h i o p s , F p ^ = 8 . 9 7 , i

c o n f i n i s , F p ^ = 5 .0 4 ,

( 3 ,8 )

( 3 ,1 7 ) = 1

s u l p h u r e l l a , F

l a e v i s , F( 3 ,3 )

c o r o n i f e r a , F

( 3 ,5 ) “= 1 8 .3 6 ,

( 3 ,4 )= 7 .9 5 ,

= 11 .91 , P < 0 . 0 1 ; (b )

.4 8 , P < 0 . 0 0 1 ; (<:) A p io n

> 0 . 05; (d) P s am m o te tt ix

P > 0 . 05; (e) E ly m a n a

P > 0 .0 5 ; ( f) M a c r o s te le s

P < 0 ,.0 5 ; (g) R e c i l ia

P > 0 . 05; (h ) A d a r r u s

o c e l l a r i s , F p ~ 1 0 -0 5 , P < 0 . 0 0 1 ; ( i) Z y g i n i d i a

s c u t e l l a r i s , F( 1 ,9 )

2 9 .1 4 , P < 0 .0 0 1 ; (j)

D i c r a n o t r o p i s h a m a t a , F p = 2 .8 4 , P > 0 .0 5 ; (k )

P a r a la b u r n ia d a le i F ,~ = 1 4 .5 2 3 , P < 0 .0 1 . * P <l *3 / O J0 . 0 5 , ** P < 0 . 0 1 , *** P < 0 . 0 0 1 .

M ean a b s o lu t e a b u n d a n c e b y h o s t p la n t fa m ily o f

C ic a d e l l id a e o v e r w i n t e r i n g as e g g s a n d a d u l t s . D a ta

p o o le d o v e r a ll s i te s a n d two y e a r s .

L e a f h o ld in g a p p a r a t u s f o r m e a s u r in g le a f t o u g h n e s s .

A r r a n g e m e n t o f le a f h o ld in g a p p a r a t u s d u r i n g

m e a s u r e m e n t o f le a f t o u g h n e s s .

In s e t : p o s i t io n o f t o u g h n e s s m e a s u r e m e n t o f le a f ,

o = p o s i t io n o f m e a s u r e m e n t .

M ean p u p a l w e i g h t (m g ) o f E. d e f o l ia r ia o n c o n t r o l a n d

t r e a t m e n t d i e t s . B a r s a r e s t a n d a r d e r r o r s . N u m b e r s

a r e sa m p le s i z e .

M ean p u p a l w e ig h t (m g) o f m ale a n d fem ale

E . d e f o l ia r ia on c o n t r o l a n d t r e a tm e n t d i e t s .

T r e a t m e n t d i e t r e p r e s e n t e d b y h a t c h i n g . B a r s a r e

s t a n d a r d e r r o r s .

M ean d e v e lo p m e n t t im e ( d a y s ) f o r EE. d e fo l ia r ia la r v a e

on c o n t r o l a n d t r e a t m e n t d i e t s . T r e a t m e n t d ie t

r e p r e s e n t e d b y s h a d i n g .

M ean w e t a n d d r y w e ig h t (g ) o f IB. p e n d u la le a v e s

d u r i n g s p r i n g a n d e a r l y s u m m e r .

M ean le a f t o u g h n e s s (g / cm ) o f E3. p e n d u la d u r i n g

s p r i n g a n d e a r l y su m m e r a s m e a s u r e d b y a

p e n e t r o m e t e r . B a r s a r e s t a n d a r d e r r o r s .

T o t a l le a f n i t r o g e n (m g /g d r y w t) o f B_. p e n d u la

d u r i n g s p r i n g a n d e a r l y s u m m e r .

6 .9

16

P e r c e n t a g e t a n n i c a c id e q u iv a le n t s as m e a s u r e d b y

W in t 's m e th o d o f IB. p e n d u la le a v e s d u r i n g s p r i n g a n d

e a r l y s u m m e r . B a r s a r e s t a n d a r d e r r o r s .

6 . 1 0 A b u n d a n c e o f _E. d e f o l ia r i a a n d o t h e r L e p i d o p t e r a

la r v a e on E3. p e n d u la d u r i n g th e p e r io d im m e d ia te ly

fo l lo w in g b u d b u r s t 1987.

17

C H A P T E R O N E

I N T R O D U C T I O N

1.1"We h a v e lo n g b e e n a c c u s t o m e d to c o m p r e h e n d m a n y

m a n if e s t a t io n s o f th e m o r p h o lo g y ( o f p la n t s ) o f v e g e t a t iv e as w ell

a s r e p r o d u c t i v e o r g a n s , as b e in g d u e to th e r e la t io n s b e tw e e n

p la n t s a n d a n im a ls , a n d n o b o d y , in o u r s p e c ia l c a s e h e r e , w ill

d o u b t t h a t t h e e x t e r n a l m e c h a n ic a l m ean s o f p r o t e c t io n o f p la n t s

w e r e a c q u i r e d in t h e i r s t r u g g l e ( f o r e x is t e n c e ) w ith th e an im a l

w o r l d . In th e sam e s e n s e , t h e g r e a t d i f f e r e n c e s in th e n a t u r e

o f c h e m ic a l p r o d u c t s , a n d c o n s e q u e n t l y o f m e ta b o l ic p r o c e s s e s ,

a r e b r o u g h t n e a r e r to o u r u n d e r s t a n d i n g , i f we r e g a r d th e s e

c o m p o u n d s a s m e an s o f p r o t e c t i o n , a c q u i r e d in th e s t r u g g l e w ith

th e an im al w o r l d . T h u s , th e a n im a l w o r l d , w h ic h s u r r o u n d s th e

p l a n t s , d e e p l y i n f l u e n c e d n o t o n l y t h e i r m o r p h o lo g y b u t a ls o

t h e i r c h e m i s t r y . " ( S t a h l , 1888, c i t e d in F r a e n k e l , 19 5 9 ).

D e s p i t e t h is u n e q u iv o c a l s t a t e m e n t a c e n t u r y a g o a n d m u c h

r e c e n t w o r k , c o n t r o v e r s y o v e r t h e im p o r ta n c e o f h e r b i v o r e s in

th e e v o lu t io n o f p la n t s a n d v i c e v e r s a s t i l l r a g e s in t h e

e c o lo g ic a l l i t e r a t u r e . S e v e r a l t h e o r ie s s e e k in g to e x p la in th e

p la n t/ a n im a l in t e r a c t io n a n d c o e v o l u t io n h a v e b e e n f o r m u l a t e d ,

b u t n o n e u n i v e r s a l l y a c c e p t e d . T h i s t h e s i s s e e k s to t e s t o n e

r e c e n t h y p o t h e s i s on th e e f f e c t s o f th e c h e m ic a l d e f e n c e s o f

p la n t s on th e p o p u la t io n d y n a m i c s o f in s e c t h e r b i v o r e s : t h a t is

th a t th e c h e m ic a l d e f e n c e s o f l o n g - l i v e d p e r e n n ia l p la n t s e . g .

t r e e s s i g n i f i c a n t l y r e d u c e t h e i n t r i n s i c ra t e o f in c r e a s e o f

h e r b i v o r e s , b u t th e c h e m ic a l d e f e n c e s o f s h o r t e r l i v e d p e r e n n i a l s

a n d a n n u a ls h a v e l i t t le e f f e c t o n t h e i n t r i n s i c r a t e o f in c r e a s e o f

h e r b i v o r e s . S u c h a d ic h o t o m y in e f f e c t on p o p u la t io n p r o c e s s e s

w o u ld lead to h i g h e r h e r b i v o r e d e n s i t i e s on s h o r t e r l i v e d p la n t s

th a n on lo n g e r l iv e d o n e s .

B e f o r e c o n s i d e r i n g t h i s h y p o t h e s i s a n d o t h e r t h e o r ie s o n

p la n t/ a n im a l in t e r a c t i o n s , t h r e e m a jo r a t t r i b u t e s o f p la n t s k n o w n

to a f f e c t th e d i s t r i b u t i o n , a b u n d a n c e a n d d i v e r s i t y o f in s e c t

h e r b i v o r e s w il l b e d i s c u s s e d ; th e s e a r e h o s t p la n t s p a t ia l

d i s t r i b u t i o n , n u t r i e n t a v a i l a b i l i t y in th e h o s t p la n t a n d th e

c h e m ica l d e f e n c e s o f p l a n t s . T h e la t te r s u b j e c t is p r e s e n t e d as

a s e r ie s o f r e s u m e s on th e d i s t r i b u t i o n , s t r u c t u r e a n d b io lo g ic a l

a c t i v i t y o f th e m ain g r o u p s o f ch e m ic a l d e f e n c e .

1.2• i H o s t P la n t S p a t ia l D i s t r i b u t i o n

T h e e f f e c t o f i s la n d s i z e on s p e c ie s d i v e r s i t y w as d e s c r i b e d in

T h e T h e o r y o f I s la n d D i o g e o q r a p h y ( M a c A r t h u r & W i ls o n , 1967).

A c c o r d i n g to t h i s t h e o r y , th e n u m b e r o f s p e c ie s on an is la n d will

b e s e t b y a d y n a m ic b a la n c e b e tw e e n r a t e s o f im m ig ra t io n a n d

e x t i n c t i o n . T h e r a t e o f im m ig ra t io n m ay d e p e n d on th e d is t a n c e

o f th e i s la n d fro m a pool o f p o t e n t ia l c o l o n i s t s . C o lo n is a t io n

ra t e s m ay a ls o be r e la t e d to i s la n d s i z e , as th e la r g e r th e

i s l a n d , th e l a r g e r th e " t a r g e t " f o r c o lo n is t s to lan d on b y

c h a n c e . T h e e x t in c t io n ra t e s o f s p e c ie s on i s la n d s a r e i n v e r s e l y

r e la te d to to ta l p o p u la t io n s iz e a n d a r e t h e r e f o r e u s u a l l y

i n v e r s e l y r e la t e d to i s la n d s i z e . P a t c h e s o f p la n t s m ay b e

t r e a te d as i s l a n d s .

I n s e c t h e r b i v o r e s p e c i e s r i c h n e s s a n d p o p u la t io n d e n s i t y m ay

i n c r e a s e w ith p a t c h s i z e ( C r o m a r t i e , 1975; M a c G a r v i n , 1982;

R e y , 1 9 8 1 ) , b u t m ay n o t d o so in th e sam e w a y f o r a ll s p e c ie s

w ith in a p a t c h ( M a c G a r v i n , 1982). R e y (1981) s h o w e d t h a t

e x t in c t io n r a t e s d e c r e a s e d a n d im m ig r a t io n r a t e s in c r e a s e d w ith

i n c r e a s in g p a t c h s iz e a s p r e d i c t e d b y t h e o r y . T h e n u m b e r o f

s p e c ie s a n d th e to ta l n u m b e r o f i n d i v i d u a l s p e r p la n t m ay a lso

in c r e a s e w ith i n c r e a s i n g p a t c h s iz e ( M a c G a r v i n , 1982). S t r o n g ,

L aw to n & S o u th w o o d (1984) s u g g e s t t h a t t h e s e o b s e r v e d p a t t e r n s

m ay be d u e to p a t c h s iz e p e r s e , o r to in c r e a s e d h a b i t a t

h e t e r o g e n e i t y w i th in c r e a s i n g p a t c h s i z e .

E x p e r im e n t a l is o la t io n o f h o s t p la n t p a t c h e s f ro m o t h e r p a t c h e s o f

th e sam e s p e c i e s h a s b e e n s h o w n to h a v e an e f f e c t on in s e c t

h e r b i v o r e s p e c i e s r i c h n e s s ( D a v i s , 1 9 7 5 ). T h e r e a r e , h o w e v e r ,

few s u c h r e p o r t s fro m o b s e r v a t i o n s o f is o la te d h o s t p la n t p a t c h e s

in n a t u r a l c o m m u n it ie s ( R e y , 1981; R i g b y & L a w to n , 1981).

C r o m a r t ie (1975) s h o w e d th a t d i f f e r e n t s p e c ie s r e s p o n d e d

d i f f e r e n t l y to h o s t p l a n t d i s t r i b u t i o n . E a c h h e r b i v o r e s p e c i e s

h a d its m ax im um c o lo n is a t io n p o te n t ia l u n d e r s l i g h t l y d i f f e r e n t

s i t u a t i o n s , n o n e w as a b le to o c c u p y p la n t s in a l l s i t u a t io n s w ith

e q u a l s u c c e s s .

M a th e m a tic a l m o d e ls in d i c a t e th a t a ra n d o m ly s e a r c h i n g h e r b i v o r e

s h o u ld f in d e v e n l y d i s t r i b u t e d h o s t p la n t s m ore e a s i l y th a n

c lu m p e d h o s t p la n t s ( C a i n , 1985). F ie ld e x p e r im e n t s h a v e

v e r i f i e d th is m odel ( C a i n , E c c le s t o n & K a r e i v a , 1 9 8 5 ) . (S e e

K a r e iv a (1986) f o r a r e v ie w o f p a t c h in e s s a n d in s e c t h e r b i v o r e

c o m m u n ity d y n a m i c s . )

1 . 2 . i i H o s t P la n t D e n s i t y

T h e r e s p o n s e o f i n s e c t h e r b i v o r e to h o s t p la n t d e n s i t y is

e x t r e m e ly v a r i a b l e . Som e s p e c i e s o c c u r in g r e a t e r a b u n d a n c e o n

h ig h d e n s i t y p lo ts ( v a n d e r M e i jd e n , 1 9 7 9 ), w h e r e a s o t h e r

s p e c ie s h a v e b e e n o b s e r v e d to o v i p o s i t d i f f e r e n t i a l l y on low

d e n s i t y p a t c h e s ( T h o m p s o n & P r i c e , 1977; S o lo m o n , 1981; R o o t &

K a r e i v a , 19 8 4 ). S t r o n g e t a[ (1984) c o n c lu d e t h a t i t is

im p o s s ib le to g e n e r a l i s e a b o u t th e e f f e c t s o f h o s t d e n s i t y o n

h e r b i v o r e a b u n d a n c e a n d s p e c i e s d e n s i t y .

1 . 2 . i i i P a tc h C o m p o s i t io n

M o n o c u l t u r e s a r e c o lo n is e d m o re r a p i d l y a n d m ay s u p p o r t g r e a t e r

d e n s i t i e s o f i n s e c t h e r b i v o r e s th a n p o l y c u l t u r e s ( R o o t , 1973;

B a c h , 1980; T a h v a n a i n e n & R o o t , 1972). T h i s m ay be b e c a u s e

th e p r e s e n c e o f a s e c o n d p l a n t r e n d e r s th e h o s t p la n t le s s

a p p a r e n t ( s e n s u F e e n y ) , e i t h e r b y p h y s i c a l l y h i d i n g th e h o s t

p la n t o r b y m a s k in g it s c h e m ic a l o d o u r s . R i s c h (1980) s h o w e d

t h a t i f o n e p la n t s p e c i e s in a tw o s p e c ie s m ix t u r e w a s n o t a h o s t

o f a c h r y s o m e l i d b e e t le th e n th e n u m b e r o f b e e t le s p e r h o s t

p la n t w as le s s th a n in a m o n o c u l t u r e . W hen b o t h p la n t s p e c i e s

in a two s p e c ie s m i x t u r e w e r e h o s t p l a n t s , b e e t le n u m b e r s p e r

p la n t w e r e g r e a t e r t h a n in a m o n o c u l t u r e . T a h v a n a i n e n (1983)

s u g g e s t e d th a t th e e f f e c t s o f n o n - h o s t p la n t s on a h e r b i v o r e ' s

a b u n d a n c e m ay b e g r e a t e r o n h e r b i v o r e s o f u n a p p a r e n t th a n

a p p a r e n t p l a n t s .

T h r e e e x p l a n a t io n s o f i n c r e a s e d h e r b i v o r e load in m o n o c u l t u r e s

h a v e b e e n p r o p o s e d ( C r a w l e y , 1983); th e r e s o u r c e c o n c e n t r a t i o n

h y p o t h e s i s , th e e n e m ie s h y p o t h e s i s a n d th e m ic r o c l im a te

h y p o t h e s i s . T h e r e s o u r c e c o n c e n t r a t i o n h y p o t h e s i s s t a te s th a t

" h e r b i v o r e s a r e m o re l i k e ly to f in d a n d rem ain on h o s t s th a t a r e

g r o w in g in d e n s e o r n e a r l y p u r e s t a n d s , a n d th a t th e m ost

s p e c ia l i s e d s p e c i e s f r e q u e n t l y a t ta in h i g h e r r e l a t i v e d e n s i t i e s in

s im p le e n v i r o n m e n t s " ( R o o t , 19 7 3 ). T h e e n e m ie s h y p o t h e s i s is

b a s e d on th e o b s e r v a t i o n th a t n a t u r a l en e m ie s a r e m o re n u m e r o u s

in w e e d y c r o p s ( p o l y c u l t u r e ) th a n in w eed f r e e s y s t e m s

( m o n o c u l t u r e ) , a n d th e c o r r e l a t i o n b e tw e e n h i g h e r p r e d a t o r

d e n s i t i e s a n d lo w e r p e s t n u m b e r s p e r p la n t . H o w e v e r , d e ta i le d

s t u d ie s o f m on o a n d p o l y c u l t u r e s h a v e fa i le d to d e m o n s t r a t e th a t

r a t e s o f p r e d a t io n a n d p a r a s i t i s m a r e s i g n i f i c a n t l y h i g h e r in

p o l y c u l t u r e s ( R o o t , 1973; B a c h , 1980b; T a h v a n a i n e n S R o o t ,

19 7 2 ). T h e m ic r o c l im a te h y p o t h e s i s s u g g e s t s th a t th e

m ic r o c l im a te in m o n o c u l t u r e m a y be c o n d u c i v e to h i g h e r f e c u n d i t y

o r a lo w e r d e a t h r a t e . R e p r o d u c t i v e r a t e s m a y b e lo w e r in

p o l y c u l t u r e s ( T a h v a n a i n e n S R o o t , 1972; B a c h , 1 9 8 0 b ) , h o w e v e r ,

th e c a u s a l m e c h a n is m is u n c l e a r a n d th e e f f e c t is n o t u n i v e r s a l

( B a c h , 1 9 8 0 a) . T h e m ic r o c l im a te in a p o l y c u l t u r e m a y b e m ore

f a v o u r a b le to e n e m ie s a n d u n f a v o u r a b l e to h e r b i v o r e s ( L u g i n b i l l

& M c N e a l , 1 9 5 8 ).

1 .3 N U T R I E N T A V A I L A B I L I T Y IN T H E H O S T P L A N T

A s w ith a ll o r g a n i s m s , i f th e n u t r i e n t s e s s e n t ia l f o r m e ta b o l is m in

h e r b i v o r o u s in s e c t s a r e l im it in g in t h e i r e n v i r o n m e n t o r fo o d ,

th e n t h e i r p e r f o r m a n c e w ill b e r e d u c e d . It h a s b e e n s u g g e s t e d

th a t p la n t s m ay d e c r e a s e n u t r i e n t a v a i l a b i l i t y to h e r b i v o r e s as

p a r t o f a d e f e n c e m e c h a n is m ( F e e n y , 1976; M o r a n & H a m ilt o n ,

19 8 0 ). N i t r o g e n is an e s s e n t ia l e le m e n t in t h e s t r u c t u r e o f

p r o t e i n s . M u c h l i t e r a t u r e n o w s u g g e s t s th a t n i t r o g e n a v a i l a b i l i t y

is o f v i t a l im p o r t a n c e to h e r b i v o r e s ( M c N e i l l 6 S o u t h w o o d , 1978;

M a t t s o n , 1980; W h it e , 19 8 4 ).

W o rk on a p h i d s h a s s h o w n h o w n i t r o g e n a v a i l a b i l i t y c a n a f f e c t

i n d i v i d u a l f e c u n d i t y , s u r v i v a l a n d p o p u la t io n d y n a m ic s ( D i x o n ,

1963, 1966, 1 9 6 9 ). T h e S y c a m o r e A p h i d ( D r e p a n o s ip h u m

p la ta n o id e s ) fe e d s on p h lo e m , t h u s it is th e le v e l o f n i t r o g e n in

th e p h lo e m s a p w h ic h a f f e c t s t h i s a p h id 's p e r f o r m a n c e . T h e

p e r f o r m a n c e o f D . p la t a n o id e s in th e f ie ld is c o r r e la t e d w ith

s o lu b le n i t r o g e n le v e ls in h o s t p la n t t i s s u e s . A s th e

c o n c e n t r a t i o n o f n i t r o g e n in th e ph loem s a p d r o p s , a p h id s

fe e d in g on th e p h lo e m b e ca m e s m a l le r a n d le s s f e c u n d ( M i t t le r ,

1958; D i x o n , 1963, 19 7 5 ). T h e v a r ia b le n i t r o g e n c o n t e n t o f

le a v e s m ay c a u s e a p h id s to a g g r e g a t e on le a v e s o f th e b e s t

q u a l i t y , e s p e c i a l l y in th e a u t u m n ( D ix o n , 1966; W r a t t e n , 1 9 7 4 ).

S u c h a g g r e g a t io n m ay a f f e c t th e p o p u la t io n d y n a m ic s o f a

s p e c i e s , e i t h e r d i r e c t l y t h r o u g h m u tu a l i n t e r f e r e n c e ( D i x o n ,

1966) a n d / o r v ia t h e i r i n t e r a c t i o n w ith p r e d a t o r s a n d p a r a s i t o id s

( H a s s e l l , 1 9 8 1 ) .

O t h e r s t u d ie s c o n f i r m th a t th e n i t r o g e n c o n t e n t o f fo o d h a s m ajo r

c o n s e q u e n c e s f o r h e r b i v o r e p e r f o r m a n c e . F o x & M a c a u ie y (1977)

r e p o r t t h a t th e p e r f o r m a n c e o f P a r o p s is a to m a r ia ( C o le o p t e r a :

C h r y s o m e l id a e ) on E u c a l y p t u s c a n b e d i r e c t l y r e la t e d to n i t r o g e n

c o n c e n t r a t i o n . S im i la r e f f e c t s h a v e b e e n r e p o r t e d f o r

T y r i a ja c o b a e a e ( L e p i d o p t e r a : A r c t i i d a e ) w h e r e s i z e , f e c u n d i t y

a n d la r v a l s u r v i v a l i n c r e a s e d w ith in c r e a s i n g n i t r o g e n

c o n c e n t r a t i o n in th e h o s t p l a n t ( M y e r s & P o s t , 1981). T h e

n i t r o g e n c o n t e n t o f g r a s s e s a n d it s a v a i l a b i l i t y h a s b e e n s h o w n

to h a v e a m ajo r e f f e c t o n th e p o p u la t io n d y n a m ic s o f l e a f h o p p e r s

( H e m ip t e r a : C i c a d e l l i d a e , D e lp h a c id a e ) ( P r e s t i d g e , 1982a, 1982b;

P r e s t i d g e & M c N e i l l , 1983b). H o w e v e r , n e g a t i v e e f f e c t s o f

n i t r o g e n on a n in s e c t h e r b i v o r e ' s p e r f o r m a n c e h a v e , b e e n

r e p o r t e d a t h i g h n i t r o g e n c o n c e n t r a t i o n s ( W a y n e - B r e w e r ,

C a p i n e r a , D e s h a m & W a lm s le y , 1985; P r e s t i d g e , 1 9 8 2 a) .

S i m i l a r l y , F a e t h , M o p p e r & S i m b e r lo f f (1981) r e p o r t t h a t

d e n s i t i e s o f le a f m in e r s on o a k w e r e s i g n i f i c a n t l y a n d n e g a t i v e l y

c o r r e la t e d w ith to ta l n i t r o g e n c o n t e n t o f le a v e s .

1 .4 C H E M I C A L D E F E N C E S

M a n y c o m p o u n d s h a v e b e e n i s o la t e d fro m p la n t t i s s u e w h ic h h a v e

b e e n p o s t u la t e d to h a v e a d e f e n s i v e fu n c t io n a g a i n s t h e r b i v o r e s

o r d i s e a s e - c a u s i n g o r g a n i s m s . In th e fo l lo w in g s e c t io n th e m ajo r

g r o u p s o f c h e m ic a l d e f e n c e f o u n d in p la n t s a r e r e v ie w e d .

1.4.i C y a n i d e

T h e p r e s e n c e o f c y a n i d e in p la n t s is w i d e s p r e a d , o c c u r r i n g in

s p e c ie s am on g 500 g e n e r a , c o m p r is i n g 100 f a m i l ie s . T h e fa m ilies

w h ic h a r e p a r t i c u l a r l y n o te d f o r c y a n o g e n e s is a r e R o s a c e a e ,

L e g u m in o s a e , G r a m in e a e , A r a c e a e , C o m p o s ita e a n d P a s s i f lo r a c e a e

( G i b b s , 1974).

In o r d e r f o r a p la n t to be c y a n o g e n ic it m u s t c o n t a in b o th

c y a n o g e n ic g l u c o s i d e s a n d th e a p p r o p r i a t e /$ - g l u c o s i d a s e

e n z y m e s c a p a b le o f h y d r o l y s i n g th e g l u c o s i d e s a n d r e le a s in g

h y d r o g e n c y a n i d e ( H C N ) w h e n th e t i s s u e s a r e d a m a g e d . T h e

g e n e t ic b a s i s o f c y a n o g e n e s i s in T r i f o l iu m r e p e n s a n d L o t u s

c o r n i c u l a t u s h a s b e e n d i s c u s s e d b y N a s s (1972) a n d J o n e s

(1 9 7 7 ) . T h e s y s t e m is c o n t r o l l e d b y g e n e s a t tw o u n l i n k e d lo c i .

O n e p a i r o f a l le le s c o n t r o l s th e p r o d u c t io n o f th e c y a n o g e n ic

g lu c o s id e s a n d th e o t h e r p a i r c o n t r o l s p r o d u c t i o n o f th e e n z y m e .

T h i s s y s te m le a d s to p o ly m o r p h is m in th e a b i l i t y to p r o d u c e

c y a n i d e , w ith t h r e e g e n o t y p e s b e in g a c y a n o g e n i c a n d o n e

g e n o t y p e b e in g c y a n o g e n i c . S u c h a s y s t e m is id e a l f o r th e

s t u d y o f p l a n t / h e r b i v o r e in t e r a c t i o n s .

T h e d e f e n s i v e c a p a c i t y o f c y a n o g e n e s is h a s b e e n s h o w n in

s e v e r a l s t u d i e s . It is k n o w n th a t H C N fo r m s c o m p le x e s

r e v e r s i b l y w ith hem e p r o t e i n s , n o t a b ly c y t o c h r o m e o x i d a s e , th e

e n z y m e w h ic h c a t a l y z e s th e te r m in a l s t e p in a e r o b i c r e s p i r a t i o n

( C o n n , 1979).

J o n e s (1962) s h o w e d th a t t h e a c y a n o g e n i c m o r p h o f L o t u s

c o r n i c u l a t u s w as c h o s e n in p r e f e r e n c e to th e c y a n o g e n i c m o r p h

b y th e v o le M ic r o t u s a g r e s t i s , t h e s n a i ls A r i a n t a a r b u s t o r u m a n d

H e l ix a s p e r s a , a n d th e s lu g A g r io l im a x r e t i c u l a t u s . C o r k h i l l

(1952) s h o w e d t h a t r a b b i t s a v o id e d c y a n o g e n ic T . r e p e n s . D i r z o

& H a r p e r (1982) d e m o n s t r a t e d th a t c y a n o g e n e s i s m a r k e d ly

r e d u c e d , b u t d id n o t w h o l ly p r e v e n t , d a m a g e to T . r e p e n s b y

f o u r s p e c ie s o f m o l lu s c . S u b s e q u e n t e x p e r im e n t s s h o w e d t h a t

s l u g s w h ic h fe d on c y a n o g e n i c le a v e s o f T . r e p e n s a t t a in e d

s m a lle r l i v e w e ig h t g a i n s o r lo s t w e ig h t f a s t e r th a n s l u g s fe d

a c y a n o g e n i c l e a v e s . B o th D i r z o & H a r p e r (1982) a n d J o n e s ,

23

K e y m e r 8 E l l i s (1978) f o u n d a n e g a t i v e r e l a t io n s h ip b e tw e e n th e

d e n s i t y o f c y a n o g e n i c m o r p h s o f T . r e p e n s a n d L.. c o r n i c u l a t u s

r e s p e c t i v e l y a n d th e d e n s i t y o f m o l lu s c s in th e f ie l d .

B r a c k e n ( P t e r id iu m a q u i l i n u m ) a ls o d e m o n s t r a t e s c y a n o g e n e s i s .

C o o p e r - D r i v e r 8 S w a in (1976) f o u n d th a t c y a n o g e n ic b r a c k e n w as

less p r e f e r r e d b y d e e r a n d s h e e p th a n was a c y a n o g e n i c b r a c k e n .

In la b o r a t o r y e x p e r i m e n t s t h e y fed b r a c k e n to th e lo c u s t ,

S c h is t o c e r a g r e g a r i a : o n l y 4% o f c y a n o g e n ic f r o n d s w e re e a te n

a l t h o u g h a r o u n d 50% o f a c y a n o g e n i c f r o n d s w e re e a t e n .

In 1976 L a w to n s u g g e s t e d th a t h i g h le v e ls o f c y a n i d e a n d o t h e r

c h e m ic a ls in b r a c k e n in th e s p r i n g w e re r e s p o n s ib l e f o r th e low

d i v e r s i t y o f in s e c t h e r b i v o r e s w h ic h fe d on b r a c k e n a t t h is t im e

o f y e a r . T h e c o n c e n t r a t i o n o f c y a n i d e in b r a c k e n d e c r e a s e s

t h r o u g h o u t th e y e a r , w h e r e a s i n s e c t h e r b i v o r e d i v e r s i t y p e a k s in

J u l y ( L a w t o n , 1 9 7 6 ) . A l t h o u g h la te r h e c o n s i d e r e d t h a t

a r c h i t e c t u r e w as th e m a jo r f o r c e s t r u c t u r i n g th e in s e c t h e r b i v o r e

c o m m u n ity ( L a w t o n , 1 9 7 8 ).

A l t h o u g h t h e r e is g o o d e v i d e n c e f o r c y a n i d e a c t in g a s a c h e m ic a l

d e f e n c e a g a i n s t h e r b i v o r e s , t h e r e c o u ld b e o t h e r f u n c t io n s f o r

c y a n i d e in a p la n t e . g . n i t r a t e r e d u c t a s e r e g u la t io n ( S o lo m o n s o n

8 S p e h a r , 1977; E c k 8 H a g e m a n , 1 9 7 4 ).

1 . 4 . i i A l k a l o i d s

T h e a lk a lo id s a r e g r o u p e d t o g e t h e r b e c a u s e t h e y c o n t a in

n i t r o g e n , f r e q u e n t l y in a h e t e r o c y c l i c r i n g , a n d n o t b e c a u s e o f

a n y com mon m e ta b o l ic o r i g i n ( W h it t a k e r 8 F e e n y , 1 9 7 1 ). T h e

a lk a lo id s a r e s p l i t in to s e v e r a l g r o u p s o f m o re c l o s e ly r e la t e d

c o m p o u n d s ; th e p y r r o l i d i n e s e . g . n i c o t i n e , th e t r o p a n e s e . g .

c o c a i n e , th e p u r i n e s e . g . c a f f e in e a n d th e s t e r o i d s e . g .

s o la n id in e .

A lk a lo id s a r e w i d e s p r e a d in t h e p la n t k in g d o m . C ro m w e ll (1955)

c la im s th a t o n e s e v e n t h o f a ll a n g io s p e r m fa m il ie s c o n t a in a lk a lo id

b e a r i n g s p e c i e s , w h i le W il l iam so n 8 S c h u b e r t (1955) r e p o r t th e

p r e s e n c e o f a lk a l o i d s in o n e t h i r d o f a ll a n g io s p e r m s p e c i e s .

T h e m a jo r i t y o f a lk a lo id b e a r i n g p la n t s a r e d i c o t y le d o n s , b u t

som e a r e r e p o r t e d from m o n o c o ty le d o n s a n d g y m n o s p e r m s . L e v i n

(1976) s u g g e s t s th a t a lk a l o i d s o c c u r m ore f r e q u e n t ly in

a n n u a l / h e r b a c e o u s p la n t s th a n in p e r e n n ia l s .

A l k a l o i d s g e n e r a l l y o c c u r in m e ta b o l ic a l ly v e r y a c t iv e t i s s u e s ,

t y p i c a l l y e p id e r m a l a n d h y p o d e r m a l t i s s u e s , v a s c u l a r s h e a th s a n d

la te x v e s s e l s ( R o b i n s o n , 1979) a n d in all y o u n g t i s s u e s

( M o t h e s , 1 9 5 5 ) . T h e p e r c e n t a g e d r y w e ig h t o f a lk a lo id s in

le a v e s t e n d s to d e c r e a s e as th e le a v e s a g e ( M o t h e s , 1955). A s

w ell as o c c u r r i n g in le a v e s , a lk a lo id s h a v e a ls o b e e n r e p o r t e d to

o c c u r in f lo w e r s ( D o l l i n g e r , E h r l i c h , F i t c h & B r e e d lo v e (1973)

a n d in s e e d s ( B e l l , 1 9 7 8 ) . M c K e y (1974) s u g g e s t e d th a t t h e

a lk a l o i d s m ay be d i s t r i b u t e d w i th in a p la n t in a c c o r d a n c e w i t h

th e v a l u e o f th e t i s s u e to b e d e f e n d e d i . e . v a lu a b le t i s s u e s

s h o u ld c o n t a in h i g h e r a lk a lo id c o n c e n t r a t i o n s .

O n c e i n g e s t e d , a lk a lo id s t e n d to e i t h e r d i s r u p t d e v e lo p m e n t a l

p r o c e s s e s o r a f f e c t th e n e r v o u s s y s te m o f an a n im a l. A l k a l o i d s

a r e k n o w n to d i s r u p t D N A r e p l i c a t i o n , R N A t r a n s c r i p t i o n ,

p r o t e i n s y n t h e s i s a n d m e m b r a n e t r a n s p o r t p r o c e s s e s , i n h i b i t

e n z y m e s a n d b lo c k r e c e p t o r s i te s f o r e n d o g e n o u s c h e m ic a l

t r a n s m i t t e r s ( R o b i n s o n , 1 9 7 9 ) . T h e a d v e r s e e f f e c t s o f a l k a l o i d s

on v e r t e b r a t e g r a z e r s is w e l l d o c u m e n t e d ; c a t t le , s h e e p a n d

m eadow v o l e s (M ic r o t u s c a l i f o r n i c u s ) sh o w a p r e f e r e n c e f o r r e e d

c a n a r y g r a s s ( P h a la r is a r u n d i n a c e a ) w h ic h h a s low tota l a lk a l o i d

c o n t e n t ( S im o n s & M a r t e n , 1971; M a r t e n , B a r n e s , S im o n s &

W o o d in g , 1973; K e n d a l l & S h e r w o o d , 1 9 7 5 ). If fe d a lk a lo id a l

p l a n t s , t h e s e a n im a ls m ay s u f f e r r e d u c e d g r o w t h ( c i te d in

R o b i n s o n , 1 9 7 9 )/ b e co m e b l i n d ( H e r m a n n , 1966), p r o d u c e

a b n o r m a l o f f s p r i n g ( K e e l e r , 1969) o r d ie ( M a r s h & C l a u s o n ,

1916) .

In th e e c o lo g y o f i n s e c t s , a lk a lo id s t y p i c a l l y p la y one o f t h r e e

r o le s ; a s an a t t r a c t a n t , as in th e c a s e o f th e a lk a lo id s p a r t e i n e

a n d th e b ro o m a p h id Acyythosiphon spagtii ( H e m ip t e r a :

A p h i d i d a e ) ( S m it h , 1966) , as a s e q u e s t e r e d t o x in w h ic h c o n f e r s

p r o t e c t io n on th e s e q u e s t e r i n g in s e c t a g a i n s t p r e d a t o r s , a s in

th e c a s e o f th e a lk a lo id s in S e n e c io ja c o b a e a e a n d th e c i n n a b a r

25

moth Tyria jacobaeae (A plinr Benn & Rothschild, 1968), and as a feeding deterrent/toxin acting as a defence against herbivores. This latter role will now be discussed in greater detail.

In a detailed study, Harley & Thorsteinson (1967) examined the effect of twenty alkaloids on the performance of a polyphagous grasshopper Melanoplus bivittatus (Say) (Acrididae: Orthoptera). Of the twenty alkaloids in an artificial diet, ten had no effect on survival to adulthood, one increased survival, three decreased survival and five were lethal to nymphs in any dose. Of the ten alkaloids that had no effect on survival, five had no effect on the rate of weight gain or adult weight, two decreased adult weight and three decreased the rates of weight gain. In feeding preference experiments, diets containing innocuous chemicals were sometimes discriminated against, while diets containing chemicals producing lethal effects were accepted. Three of the alkaloids found to be lethal were present in known host plants ofM. bivittatus. The authors speculated that these alkaloids may be restricted to certain stages of the plant's life cycle e .g . seedlings, and that the grasshopper may discriminate against such stages.

The work of Harley & Thorsteinson is important as it shows that the effects of alkaloids need not be an all or nothing response, as supposed by some theories of plant/herbivore interactions (Feeny, 1976; Rhoades S Cates, 1976) (see section 1 .5 ), but may affect aspects of herbivore performance, such as adult weight which may be correlated with fecundity.

Unfortunately, few studies are as detailed as the above, although many report the adverse effects of alkaloids on herbivorous insects. The Colorado beetle ( Leptinotarsa decemlineata) (Coleoptera; Chrysomelidae) feeds on cultivated potatoes, Solanum tuberosum, containing the alkaloid solanine with apparently no adverse effects on performance. However demissine, which is similar to solanine in structure and occurs in Solanum demissum, acts as a feeding deterrent to L. decemlineata, as does tomatine from tomatoes. A 2mM/kg solution of tomatine painted on potato leaves reduces larval

26

feeding by 50%, whereas a solution of 3mM/kg causes 100% larval mortality (cited in J.B . Harborne, 1 978).

Dollinger et al (1973) examined a system involving a lycaenid butterfly, Glaucopsyche lygdamus ( Lepidoptera: Lycaenidae) and three species of lupin, Lupinum bakeri, L. caudata and L. floribundus ( Leguminosae). They discovered that populations of lupin which suffered little predation from (j . lygdamus contained fewer alkaloids than lupin populations suffering greater predation, which had increased alkaloid concentrations. However, it was not the absolute concentration of alkaloids which conferred a defence on the lupin, but the variability of the alkaloid mixtures present in the plant populations. The "high alkaloid" lupin populations which suffered the least damage had very variable alkaloid profiles. The populations suffering most damage contained nine alkaloids but they were constant between individual plants. The authors hypothesize that the individual variability in alkaloid content is an anti-specialist chemical defence mechanism, "Such individual variability may beadvantageous to plant populations by reducing the possibility of selection for strains of specialist herbivores capable of detoxifying plant defensive compounds", Dollinger et a [ (1973).

1 • 4. iii Glucosinolates

Glucosinolates are found in families belonging to the order Capparales, namely the Capparaceae, the Resedaceae, the Moringaceae and the Cruciferae (Kjaer cited in van Etten & Tookey, 1979). The majority of work on glucosinolates has concentrated on the latter family. Indeed, all species ofCruciferae so far investigated have been found to contain one or more glucosinolate. These chemicals are typically present in plants in small quantities, eg isothiocyanate is present in Brussel sprouts at 0.0568% dry weight and in cauliflower at 0.0083% (Lichenstein, Morgan & Mueller, 1964).

As a chemical group, all glucosinolates contain >3 -D-thioglucose and sulphate moieties (Ettliger & Kjaer, 1968) which are well known toxins. Sinigrin is toxic because it releases the mustard

oil, allylisothiocyanate, into the gut (Erickson s Feeny, 1974). The mustard oils are powerful antibiotics (Virtonen, 1965) and damage mammalian tissues typically the thyroid, liver and kidneys (Tookey, van Etten & Daxenbichler, 1979).

The glucosinolates may act as feeding attractants to adapted insect herbivores (Feeny, Poauwe £ Demong, 1970; Schoonhoven, 1969; Thorsteinson, 1953), and as attractants to egg layingfemales of some Pierid butterflies (Chew, 1975). Glucosinolates have also been reported as sequestered toxins (Rothschild, 1972). The toxic properties of glucosinolates against non-adapted insect herbivores are well documented. For example, Erickson 6 Feeny (1974) reared larvae of theUmbelliferae specialist, the black swallowtail butterfly, Papilio polyxenes) (Lepidoptera: Papilionidae), on celery leaves cultured in sinigrin solution of different concentrations. They found that feeding rates were not significantly affected, but growth and development were substantially reduced as was pupal weight and the number of eggs produced per female. At sinigrin concentrations of 0.1%, 100% larval mortality occurred(concentrations in the plant varied between 0.03-0.1% dry weight). In a further study on the same system, Blau, Feeny & Contardo (1978) showed that the toxicity of allylglucosinolate was greatest to P. polyxenes, intermediate on the generalist Spodoptera eridania (Lepidoptera; Noctuidae), where larval growth was inhibited at high allylglucosinolate concentrations and least on the Cruciferae specialist Pier is rapae (Lepidoptera: Pieridae). Even at artificially high concentrations of theglucosinolate the performance of Pieris rapae was not affected.

Scriber (1981) observed reduced larval growth of S_. eridania on a diet of cabbage, relative to growth on other food plants. He ascribed this observation to the glucosinolate content of the cabbage. Other studies tend to corroborate the effect ofglucosinolates on non-adapted herbivores, e.g . studies quoted in Erickson 5 Feeny (1974) all report reduced larval growth and survival of Lepidoptera larvae when fed cruciferous food plants; Torri & Morri (1948) ( Bombyx mori), Wallbauer (1960) (Manduca sexta), Soo Hoo (1963) (Proderria eridania) and Brower (1969)( Danaus plexippus) .

28

Glucosinolates have also been reported to have an effect onsap-feeding insects. Klingauf, Senganco S Bennewitz (1972) showed that a 0.1% solution of sinigrin reduced the uptake of sucrose in the aphids, R.hopalosiphum padi and Aphis fabae (Hemiptera: Aphididae), but increased the sucrose uptake ofBrevicoryne brassicae and Myzus persicae (Hemiptera:Aphididae).

I.U .iv Flavonoids

Flavonoids occur throughout the angiosperms and gymnosperms and regularly in ferns, mosses and liverworts. There are abouttwo thousand known naturally occurring flavonoids. The mostwidespread classes of flavonoids are anthocyanins, flavones and flavanols. Chemically flavonoids are aromatic, heterocycliccompounds derived from fiavone. Flavone has a -pyrone ring with ether-linked oxygen as a part of its structure (Harborne, 1979).

Flavonoids are extremely toxic. The isoflavin vestital, has been shown to be toxic to the larvae of Heteronychus aratoo (Coleoptera: Curculionidae) which feed on the roots of Lotus spp (Russell, Sutherland, Hutchinson & Christmas, 1978), and as a feeding deterrent to Pieris brassicae (Lepidoptera: Pieridae)(Schoonhoven, 1972). Flavonal glycosides in Ulmus europea have been shown to act as feeding attractants to Scolytus multistriatus (Coleoptera; Scolytidae) (Doskotch, Mikhail & Chatterji, 1973). Furth & Young (1988) claim that the flavonoid content of Rhus spp. (Aracardiaceae) correlated with the feeding preference of two chrysomelid beetles.

1.4 .v Saponins

Saponins are glycosides in which the aglycone portion of the molecule is either a sterol or a triterpene. The number and nature of sugar units combined with the aglycone is very variable (B irk , 1969). Saponins have been reported from five hundred species of plants from eighty different families (Basu & Rostagi, 1967), including leg jmes (Walter, 1961) and some woody

29

plants (Takahashi, Miyazaki, Yasue, Imamura & Honda (1963) cited in Applebaum & B irk, 1979). They have been described from all parts of the plant, including roots and seeds. The toxic effect of saponins is due to a hydrophobic/hydrophilic asymmetry and consequently they lower surface tension, thereby affecting cell membranes. Applebaum & Birk (1972) suggest that saponins may alter the permeability of the insect gut with toxic results and that they may also cause a hormone Imbalance, resulting in incomplete development. !shaaya& Birk (1965) show that saponins can function as inhibitors of proteolytic enzymes and thus may act as both a qualitative and quantitative defence,

(cited in Appeibaum & B irk, 1979).

Saponins have been shown to confer resistance against the root-feeding larvae of the grass grub Costelytra zeaiandica (Kain & Atkinson, 1970) and the white grub Melalontha vulgaris (Coleoptera; Scarabeiidae) (Horber, 1965), and to inhibit the development of Callosobruchus chinensis (Coleoptera: Bruchidae) and Tribolium castaneum (Coieoptera: Terebrionidae) (Ishaaya, Birk, Bondi & Tencer (1969) (all cited in Appeibaum & B irk, 1979).

The leafhopper, Empoasca fabae (Hemiptera: Cicadellidae)suffered increased mortality when saponin was introduced into its artificial diet (Roof, Horber & Sorenson (1972), cited in Applebaum & Birk (1979)). Acyrthosiphon pisum (Hemiptera: Aphididae) responded in a similar manner. Applebaum & Birk (1972) report that saponin acted as a feeding deterrent when included in artificial diets fed to Myzus persicae (Hemiptera: Aphididae), a polyphagous aphid. This suggestion that saponin may act as a feeding deterrent as well as a toxin has not been fully pursued.

1 .4 .iv Terpenes & Resins

Terpenoids may function in many metabolic processes in the plant, as well as a pollinator attractant and herbivore deterrent. They are organic molecules based on repeating 5-carbon subunits. The best known are the pyrethroids, obtained from Chrysanthemum spp (Compositae) which have excellent

30

insecticidal properties. However, less than 1% of known terpenoids have been investigated for their feeding and deterrent properties (Mabry & Gill, 1979).

Sequiterpene lactones are common in Compositae but occur infrequently in other families. The sequiterpene lactone glaucolide A of Vernonia (Compositae) was shown to be adeterrent to several Lepidoptera species, and also to increase their larval development times and decrease their growth.Rabbits and Whitetail deer also avoided Vernonia plants containing glaucolide-A (Mabry & Gill, 1979; Burnett, Jones & Mabry, 1978 and references therein).

Resins of conifer trees, a major defence against insects,commonly contain monoterpenes. After being attacked some conifer species increase monoterpene levels in their tissues which then become more active against bark boring beetles(Coleoptera: Scolytidae), (Smith, 1965). Smith (1975) suggested that tree resistance is related to both monoterpene content and to the level of resin flow. The results of Larsson, Bjorkman & Gref (1986) show that resin acid, containing diterpenoids, of Scots Pine ( Pinus sylvestris L .) has a complex effect on Neodiprion sertifer (Hymenoptera; Diprionidae). High resin acid concentrations increased development times and mortality but had no effect on pupal weight. Final instar larvae showed no decrease in mean relative growth rate when fed diets containing three times the resin acid content of the control diet. Indeed, there is some suggestion that final instar larvae actually search out high concentration resin acid needles and bark, perhaps in order to utilise the resin acids in their own defence.

The effect of resins produced by chapparral shrubs on their herbivores has been particularly well studied. Rhoades & Cates (1976) studied two Larrea species which produced a resin containing up to 90% phenolic compounds and comprising up to 44% of the dry weight of young leaves and 15% of mature leaves. Most herbivores studied preferred mature leaves of Larrea. However, a specialist feeder, Insara couilleae (Orthoptera: Tettigonidae), preferred young leaves. Removal of resin from

31

the food plant increased its palatability to generalist feeders and decreased it to a specialist feeder, which used resin as a feeding stimulant. Similar results were obtained with herbivores of the bush Eriodictyon californicum (Hydrophyllaceae) by Williams, Lincoln & Ehrlich (1983). The flavonoid aglycone resindecreased feeding by Euphydryas chalcedony (Lepidoptera: Nymphalidae), possibly due to the mechanical difficulty it caused larvae. The resin also decreased larval survivorship, growth rate and pupal weight in a simple dose-dependent method (Lincoln, Newton, Ehrlich & Williams, 1982). Johnson, Brain S Ehrlich (1984) showed that, despite low resin concentration foliage being preferred for feeding by larvae and for ovipositing by adults of Trirhabda diducta (Coleoptera: Chrysomelidae), an increase in resin concentration of five times had no effect on adult or larval growth rate. No effect of the resin acting toprecipitate proteins was found, as resin concentration increased in the diet the beetles ate more.

1 .4 .v ii Tannins

Tannins have been defined as any naturally occurring phenolic compounds with a molecular weight between 500 and 3000 which are able to form effective cross linkages with proteins and other macromolecules (Swain, 1965). Tannins have been found in all classes of vascular plants, but do not occur in prokaryotes, fungi or animals (Swain, 1979). Swain (1979) recognises four groups of tannin, proanthocyandin or condensed tannins, hydrolysable tannins, oxytannins and B-tannins. Condensed tannins are the most widespread of the four groups,hydrolysable tannins occur in dicotyledons, oxytannins are only formed on injury to the plant and B-tannins comprise a wide variety of lower molecular weight compounds.

During the 1970’s, it was believed that tannins acted in a dose-dependent manner on all herbivores and that they were very difficult to overcome in the evolutionary 'arms race1. The deleterious effects of the chemicals being produced by forming complexes with proteins in the food and with enzymes in the herbivore's gut, thereby decreasing digestive efficiency. These

32

ideas arose mainly from the work of Feeny (1968, 1970, 1976) who showed in 1968 that the addition of tannins to the diet of Operophtera brumata L. (Lepidoptera: Geometridae) reducedlarval growth. From this he postulated that the presence of tannins in the mature leaves of trees was one reason why the spring-feeding habit predominated amongst deciduous tree-feeding temperate Lepidoptera (Feeny, 1970). Prior to Feeny's work, Bennett (1965) had found tannic acid to be a repellent and to reduce survivorship in Hypera postica (Coleoptera: Curculionidae). More recent work has also shown evidence of reduced herbivore performance in herbivores feeding on diets containing tannin (Manuwoto & Scriber, 1986; Berenbaum, 1983; Roehrig & Capinera, 1983; Chan, Waiss, Binder & Ellinger, 1978; Schoonhoven & Derksen-Koppers, 1976). No-one has found conclusive evidence of tannins, however, at concentrations found naturally in the host plant affecting (all aspects of) herbivore performance in the classic dosage dependent manner postulated by Feeny (1976). During the 1980's, several workers have questioned the classical view of the action of tannins (Bernays, 1978, 1981; Berenbaum, 1983;Zucker, 1983; Lawson, M erritt, Martin, Martin & Kukar, 1984). Indeed Bernays & Woodhead (1982) describe a mechanism by which phenols are used to an insect's advantage; the Tree Locust, Anacridium melanorhodon (Orthoptera: Acrididae),utilises the breakdown products of phenols to stabilise proteins in the cuticle, thereby conserving amino-nitrogen. It has also become increasingly evident that hydrolysable and condensed tannins may have different effects on insect herbivores (Bernays, 1981). Bernays (1981) states that hydrolysable tannin cannot be counted as a quantitative defence as perceived by Feeny (1976). Condensed tannins may cause quantitative effects on several species of insect, but the response between species is different. However the pH of the midgut of Lepidoptera larvae may be sufficiently alkaline to eliminate the digestibility-reducing properties of this group of tannins (Berenbaum, 1980) (see also Krieger, Feeny & Wilkinson, 1971 & Brattsten, Wilkinson & Eisner, 1977, on the role of mixed function oxidases in the gut of Lepidoptera). The separate effects of condensed and hydrolysable tannins are often difficult to determine, as both types may co-occur in the same plant.

33

The changes of opinion of ecologists on the importance of tannins to individuals and populations of herbivores is of extreme importance to this thesis as at the time of formulating the hypothesis tested here, Lawton & McNeill (1979) believed the classic Feeny (1976) view on tannins.

1.4 .v iii Miscellaneous Defences

Other groups of chemicals not previously discussed but known to have an effect on herbivores include insect hormone analogues, furanocoumarins and non-protein amino acids.

Substances which interfere with the hormonal control of growth and development in insects have been isolated from Pteridophytes, Cymnosperms and several Angiosperm families. Plants possessing these substances tend to be woody perennials rather than herbaceous plants (Slama, 1979). The chemical ageratochromere from Ageratum plants induce premature metamorphosis in nymphs of Oncopeltus (Hemiptera: Lygeidae)(Bowers, 1975). Vertebrate hormones and analogues have also been discovered in plants (Heftmann, 1975).

Furanocoumarins are known from eight angiosperm families, but occur regularly only in the Umbelliferae and Rutaceae (Berenbaum, 1981a). These chemicals have been shown to be toxic towards insects and may play an important role in structuring the insect herbivore community on umbellifers (Berenbaum 1978, 1981a, 1981b, 1981c, 1983; Berenbaum &Feeny, 1981).

It is postulated that if non-protein amino acids are incorporated in proteins, they render the protein inactive. Approximately 260 non-protein amino acids have been isolated from higher plants, the majority of which are family, genus or species specific, and have been isolated from all parts of the plant. Plants containing non-protein amino acids are extremely toxic to mammals and insects. One of the best known non-protein amino acids is canavanine, which occurs in certain legume species. It is an analogue of the amino acid arginine,

34

and is known to be toxic to a wide range of organisms including insects. The inclusion of 1.0mM of canavanine in the diet of Manduca sexta causes abnormal development and decreased survival. The seed feeding beetle Caryedes brasiliensis (Coleoptera: Bruchidae) can, however, detoxify canavanine(Rosenthal & Bell, 1979).

Plants have also produced an array of physical defences against herbivores, e .g . thorns, spines and pubescence. For a recent review of the importance of physical defences see Myers (1987) and references therein.

Despite the vast amount of evidence documenting the effects of chemical defences on herbivores, it is impossible to prove that these chemical actually evolved under the selection pressure provided by herbivores. Jermy (1984) emphasises this point stating that "as opposed to many entomologists, botanists and phytochemists are reluctant to consider phytophagous insects (or herbivores in general) as significant selection factors which havecaused the evolution of new metabolic pathw ays.......... neither dothey regard such substances as defence mechanisms".

1.5. REVIEW OF PLANT/HERBIVORE COMMUNITY ANDEVOLUTIONARY THEORY

In 1976 Paul Feeny and David Rhoades & Rex Cates independently published papers reviewing work on plant chemical defences and insect herbivores. Both papers then attempted to place their own and other people's work into one cohesive theory, which could explain the abundance and structure of chemical defences against insects across all communities. As both papers seek to explain the same observed patterns of chemical defences in plants and are fairly similar in their argument they will be reviewed together.

Both papers start with the same basic observation; that ephemeral plants tend to possess low concentrations of chemical defences which vary structurally between and within plant

families, whereas long-lived perennial plants typically contain higher concentrations of defensive compounds with little diversity in structure between species.

Ephemeral plants are generally defended by compounds such as cyanogenic glucosides, alkaloids, glucosinolates, non-protein amino acids, insect hormone analogues etc (see section 1 .4 .i-v for a review of their structure and action). These compounds are postulated to act as feeding deterrents to non-adapted herbivores, but to have little or no effect on the performance of adapted herbivores. Feeny (1976) terms these compoundsqualitative defences, whereas Rhoades S Cates (1976) call them toxins. Long-lived plants are typically defended bydigestibility-reducing defences (Rhoades & Cates, 1976) or quantitative defences (Feeny, 1976). These defences include the tannins and resins (see section 1 .4 .v i-v ii for a review of their structure and function). Both papers then proceed to consider the predictability of the plant as a resource for the herbivore and its commitment to defence. Feeny (1976) coins the term "apparency" which he defines as describing the "susceptibility to discovery" of a plant by a herbivore. This term may be applied either to individual plants or to tissues within a plant. For example, annual herbs are small in size, are only available to herbivores for a short time each year and their occurrence is unpredictable both in time and in space. Feeny (1976) considers that annuals have low apparency when compared with trees which are large, available all year round and are predictable in space for many years. Trees are therefore referred to as apparent. The young leaves of a tree are, however, considered unapparent as they are only available for a short time each year and their occurrence in time is relatively unpredictable. Rhoades & Cates (1976) note the same dichotomy between predictable plants and tissues and unpredictable ones, but do not assign terms.

The papers then consider the metabolic cost of chemical defence production. It is assumed that energy put into the production of chemical defences is energy which could otherwise have gone into growth or reproduction, and that evolution would select for

the optimal allocation of resource, depending on the relative

selective pressures of herbivores and other aspects of the individual's biology.

Feeny (1976) states "For early successional herbs selection is unlikely to favour a large metabolic allocation for defensive compounds, especially since the selective pressures of predation are reduced as a result of escape from many enemies in time and space. The adaptive emphasis in such species is thus likely to favour defensive compounds which are especially effective in small quantities."

In long-lived plants such as trees, a greater commitment to defence would seem a better strategy, as according to apparency theory such plants are more likely to be discovered by herbivores. In addition, according to r -k theory (Pielou, 1967) such long-lived organisms are not under such intense pressure to maximise growth and reproduction each season.

Having noted the differences in defence cost, structure and function between ephemeral and long-lived plants the papers then consider the effects of qualitative (toxins) and quantitative (digestibility-reducing) defences on insect herbivores.

They postulate that qualitative defences have little or no effect on adapted herbivores, but they serve as barriers to non-adapted insects. That is, they deter non-adapted herbivores from feeding on them, and if such a herbivore does feed on a plant containing a toxin it cannot detoxify, it may die. In contrast, quantitative defences act on all herbivores. Tannins complex with proteins, either enzymes in the gut of the herbivore or proteins in the food. They therefore serve to make the food less digestible. It is an important premise of the theory that quantitative defences should act in a dosage-dependent manner, that is the greater the herbivore's intake of the chemical, the greater will be its effect. Quantitative defences typically reduce the growth rate of herbivores, which serves to increase development time, thereby exposing the herbivores to natural enemies for a longer period

37

and also possibly resulting in smaller adult insects which are less fecund than larger adults. Both papers suggest that it is very difficult for herbivores to evolve a detoxification mechanism against quantitative defences. The authors also consider that low nutritional value of foliage, e .g . low nitrogen concentration, low water concentration and high toughness serve to reinforce the presence of specific chemicals as a quantitative defence.

Feeny (1976) then provides a further discussion of apparency and the rationale behind correlating an increasing commitment to defence with increasing apparency. Rhoades & Cates (1976) however, take their ideas in a different direction, although they do recognise that the amount of digestiblity-reducing defences is related to the predictability of the plant or tissue. They conclude their paper with a discussion of the importance of specialist and generalist herbivores to a plant and coevolution.

Rhoades & Cates (1976) consider that the ability of an annual plant to escape in time and space would be more effective against specialist herbivores than generalists, as specialist herbivores have no alternative food source. They predict that the more ephemeral the host plant, the greater will be the mortality of the specialist in searching for its host plant. "The predictability and availability of any individual resource is of less consequence for a generalist, however, since it can opportunistically utilize whatever resource happens to be available. Therefore, predictability of resource should select for specialism and ephemerality for generalism. It follows that ephemeral plants and tissues should escape specialists more effectively than generalists. Thus the defences evolved in ephemeral plants and tissues should be directed particularly against generalism. This in turn , should and has, given rise to a divergent system of chemical defences in such plants and tissues" (Rhoades & Cates, 1976). The generalist herbivore should than have selective forces acting upon it which would make it capable of coping with the "average defensive chemistry" of its host plant range. Thus, plant species or individuals with defences which deviate most widely from this average should be at a selective advantage when compared with plants of the "average chemical" type.

38

Rhoades S Cates (1976) believe that such a process is responsible for the diverse array of defensive chemicals in ephemeral plants and tissues.

By similar reasoning, it can be seen that the defences of predictable plants and tissues should be directed particularly against specialist herbivores. Rhoades & Cates (1976) predict a convergence of chemical defences for predictable plants, as in contrast to the evolution of defences in ephemeral tissue, the defence evolved by any one plant species will not be affected by the defences evolved in other plant species in the community. They propose "that the defensive system, that has been converged upon, is the digestibility reduction mode of defence" which shows very limited diversity. Rhoades & Cates (1976) then consider the next step in the "evolutionary arms race". They predict that convergent defences should select for generalism, "since if the resource defences are all very similar, it should not be adaptive for the herbivore to expend time and energy seeking a particular subgroup of the resources" (Rhoades & Cates, 1976). Conversely, divergent defences should select for specialism in the herbivore, "since all the resource defences are very different, the ability of a generalist to accommodate any one of the defences should be significantly less than of a specialist herbivore . . . . and the selective advantage should accrue to specialists".

Such coevolutionary theories are extremely difficult to test as it is difficult, if not impossible, to place any individualherbivore-host plant interaction on the correct "step" of the arms race. Such ideas are further complicated by the fact that a plant will be evolving in response to its whole guild of herbivores, each of which could be exerting different selective pressures on the plant. Further to this point, both Feeny (1976) and Rhoades & Cates (1976) are in agreement that although they have discussed chemical defences in the context of insect herbivores, the plant's chemistry will also have evolved under selective pressures from fungal, viral and bacterial pathogens, other invertebrates and vertebrate herbivores and maybe in response to other plants e .g . allelopathy.

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Although the main thrust of the papers is that ephemeral plants are defended by qualitative/toxic defences and long-lived perennials by quantitative/digestibility-reducing defences, both accept that toxins may be present in perennial plants and

digestibility-reducing compounds in ephemeral plants.

Two important questions remain to be answered satisfactorily before these theories can be fully accepted: firstly is there anyeffect of toxins on the performance of adapted herbivores and secondly, do quantitative defences really act in adosage-dependent manner against herbivores? Very little work has been done in an attempt to answer the first of these two questons, and hence they is little evidence for or against this assumption. Feeny (1976) recognised this when he said; "I must emphasize though that the experimental evidence for this suggestion is very limited". He quotes work by van Emden & Bashford (1969) and van Emden (1972) as an example of a qualitative defence affecting fecundity of an insect herbivore ( Brevicoryne brassicae (Hemiptera: Aphididae) on Brusselsprouts). There is some evidence that qualitative defences are not an all or nothing defence against non-adapted herbivores from the work of Dirzo & Harper (1982) (see page2 ! ) / Harley & Thorsteinson (1967) (see page25 ) and references on page27 .

The effects of tannins on herbivore performance, once believed unequivocally to be a universal dosage-dependent phenomenon reducing insect performance is now under question (see section1.4 .v ii and Chapter 5). In a brief review of chemical defences and insects Strong, Lawton & Southwood (1984) conclude; "In short, although the distinction between qualitative and quantitative defences was a reasonable theoretical beginning for this field current discoveries are making it increasingly difficult to maintain this distinction for specialised insects".

Three years after the publication of Feeny's and Rhoades & Cates' 1976 papers, Lawton & McNeill (1979) published "Between the devil and the deep blue sea: on the problems of being a herbivore", in which the hypothesis tested in this thesis was formulated. In their paper they review the mechanisms which

40

determine the characteristic levels of abundance of herbivorous insects. They investigated the independent effects of parasitoids and predators and food plant quality on the population dynamics of herbivores and then considered the combined effect of these two factors on herbivorous insect populations. After a brief review on herbivores, they conclude that there is "very little room for doubt about the importance of natural enemies, particularly parasitoids in reducing population sizes for phytophagous insects". A consideration of several models of host-parasitoid interactions predict that the equilibrium population size of the host increases as r (intrinsic rate of increase) increases, and that very high r values may lead to oscillations in population size. If the host-parasitoid model incorporates an element of spatial heterogeneity, as in that of Free,Beddington '• & Lawton (1977), it is seen that small changes

in the host's r have large effects on the host's equilibrium population size. They conclude that if the host equilibrium density is low, say due to the unpalatability of the available food, the the effect of parasitoids and predators will be to make the host even rarer.

Lawton & McNeill then discuss the effect of plant chemistry on the rates of increase of adapted herbivores. They argue that if more insects mean more damage to a plant, then it must be selectively advantageous for plants to reduce the rates of increase of their adapted herbivores. This may be achieved by reducing growth rates of the herbivores and thereby increasing generation times and reducing the number of generations a year; any reduction in survival and fecundity would also reduce r. The authors then review the effects of quantitative and qualitative defences, and the availability of nutrients on the rates of increase of herbivores (see section 1.3 and 1.4). They conclude that "plant chemistry has been shown to have a marked effect on one or more components of r , even in adapted herbivores. The clearest examples are provided by plant nutrients (particularly nitrogen) and quantitative defences, but qualitative (toxic) defences may also play a part. In consequence, control by parasitoids and predators is facilitated and equilibrium population sizes are reduced", Lawton & McNeill (1979).

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Finally, Lawton & McNeill attempt to predict what the characteristic levels of abundance of herbivorous insects would be on apparent and non-apparent plants. They say that there are no easy answers, but some simple predictions suggest themselves:

"Obviously we should compare like with like (eg Lepidoptera with Lepidoptera) on a common scale - the insects per unit weight or area of a plant for example. Within these constraints, and other things being equal, we would predict that insects attacking ephemeral, early successional herbs and weeds (non-apparent plants with largely qualitative defences (Feeny, 1976) will have higher r values than those exploiting perennial long-lived plants (apparent species with considerable investment in quantitative defences)... Again other things being equal, high r values imply large equilibrium population sizes and a greater propensity for the population to become unstable and to outbreak in populations controlled by predators and parasitoids. Hence we might expect the average population sizes of insects which attack non-apparent plants to be higher than those attacking apparent plants and to fluctuate more", Lawton & McNeill, (1979). They go on to say that the predictibility of herbivore control by predation and parasitism on ephemeral plants will "serve to reinforce the differences that already exist" between apparent and non-apparent plants.

This thesis sets out to test these predictions over a successional gradient within a comparatively small spatial scale, as suggested by the authors. The main aim of the project was to measure the absolute abundance of insect herbivores, that is the number of individuals per unit of plant, on plants typical of different stages of succession, i.e . apparent and non-apparent plants. Within the time-scale of a Ph.D. it is not possible to attempt to measure the stability of a population. Thus the prediction that insect populations on ephemeral plants are more likely to outbreak than those on long-lived plants is not tested, neither is the importance of predators and parasitoids as controlling agents on herbivores on ephemeral and long-lived plants. It is recognised that predators and parasitoids alone could produce

42

patterns of insect herbivore abundance in accordance or disagreement with Lawton & McNeill's (1979) prediction.Consequently, an obvious sequel to this thesis is a study of the importance of predator and parasitoids to herbivore populations on ephemeral and long-lived plants. It is only then that Lawton & McNeill's (1979) hypothesis can be accepted or rejected. There has already been one attempt to test Lawton & McNeill's (1979) hypothesis by Godfray (1985). In this the absolute abundance of leafmining insects on the same successional sites at Silwood Park as will be examined in this thesis were examined and found to vary in the manner predicted.

Also relevant is the work of Coley (1980, 1983a, 1983b, 1988) and Coley, Bryant & Chapin (1985) who aimed to explain the observed patterns of defence allocation in the field. Coley et £[ (1985) sought to use resource allocation as an explanation for differing defence investments in plants. They divided plants into slow and fast growers and predicted that slow-growing plants are favoured over fast-growing plants in an environment where resources are limited and vice versa, and that the optimal level of defence investment increases as the potential growth rate of the plant decreases. The reasons given for this are three-fold: firstly, as growth rates become limited by resource availability, then replacement of resources lost to herbivores becomes more expensive; secondly, a given rate of herbivory represents a larger fraction of the net production of a slow grower than that of a fast grower; th irdly, because the relative cost of defence increases as growth rates increase, lower levels of defence in resource rich environments might be expected. The authors also predict that growth rates of plants may influence the type of defence as well as the amount. It is suggested that as quantitative defences (sensu Feeny) are present in higher concentrations than qualitative defences, they represent a higher initial construction cost than qualitative defences, and they also have lower continued maintenance costs than qualitative defences which are continually being produced and broken down. They suggest that qualitative defences would not be expected to be common in long-lived leaves as the continued metabolic costs summed over leaf life time would be

43

larger than a fixed investment in quantitative defences. However, long-lived leaves can afford the metabolic cost of producing quantitative defences as they have "more time over which to spread these costs" Coley et a[ (1985). They conclude that "resource availability in the environment is the major factor influencing the evolution of both the amount and type of a plant defence", Coley et a[ (1985).

Coley (1988) presents evidence from tree species in lowland rain­forest which wholly support the ideas propounded in Coley et a| (1985). Southwood, Brown & Reader (1986) working on a temperate system, agree with Coley (1983b) that foliage palatibility and rate of herbivore damage are inversely correlated with leaf life expectancy. However, they are unable to agree with all the ideas presented in Coley et a[ (1985), as they found vast differences in leaf life expectancies between their sites but no difference in net primary production. Southwood et a[ (1986) found that palatability level decreased and herbivore damage level increased with increasing age of the plant community and they suggest these results conform with Feeny's (1976) apparency theory. Southwood et a[ (1986) conclude their paper with an attempt to reconcile the ideas of Feeny (1976) and Coley et a[ (1985) with their own findings in the context of Southwood's (1977) habitat templet.

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CHAPTER TWO

METHODS

2.1 EXPERIMENTAL SITES

The fieldwork in this project was carried out at Imperial College, Silwood Park, Berkshire, UK, during 1985 and 1986. Silwood Park is situated in 93Ha of arable land, acidic grassland and woodland areas, mainly birch and oak, at 51°21'N and 0°39*VV at an altitude of 91m. The study sites lie on Bagshot sands.

The study utilised sites of known successional age which are part of a series of sites initiated by Sir Richard Southwood and Dr. V .K . Brown in 1977. The sites are described further in Southwood, Brown S Reader (1979), Brown (1982a; 1982fc>; 1984; 1985), Brown & Southwood (1987), Stinson (1983), Godfray (1983) and Hyman (1983).

2.1. i . Site Preparation

The sites were originally prepared by ploughing and applying herbicide during the autumn before site establishment. The sites were then reploughed, harrowed and lightly rolled during the following spring before being left to recolonise naturally. Rabbits had been excluded from the the sites by fencing since 1976.

A woodland, Hell Wood, was also sampled. This is approximately 200m from the other sites. It consisted mainly of Betula pubescens, Betula pendula with the occasional Quercus spp, Fagus sylvaticus, I lex aquilifolium and Castanea sativa. The understory consisted mainly of Pteridium aquilinum.

2.1. ii Site Age and Nomenclature

A range of sites representing different successional stages was chosen for study. The sites will be referred to in the following manner - ruderal sites sampled in 1985 and 1986, at 0-1 years

45

old, early successional sites sampled in 1985 and 1986 at 1-2 years old, early midsuccessional sites sampled in 1985 at 6 years old and 1986 at 7 years old, late midsuccessional sites sampled in 1985 at 9 years old and in 1986 at 10 years old and a late

successional site at 64+ years old. The ruderal site in 1985 became the early successional site in 1986. The same site was sampled in both years for early and late midsuccession and late succession. It can be seen that some sites were sampled in both years and some only in one year giving a mixture of site and year comparisons. In order to avoid confusion over nomenclature a site is taken to mean the plot of land of one successional age and serai stage is employed when data from both years samples are pooled, i.e . the plant species richness on the ruderal serai stage is the total number of plant species recorded on a ruderal site in 1985 and 1986. Therefore five

serai stages were sampled over two years from eight different sites (see Table 2 .1 ).

2 .1 .Hi Marking Sites

Apart from the birch site, each site was divided into 3m x 3m subplots which were marked by stakes. There were 45 subplots on all sites except the 1985 site where only 40 subplots were defined. Quadrats of 1m x 1m, each divided into 4 smaller quadrats of 0.5m x 0.5m were marked in the centre of each subplot. This procedure was followed on allsubplots, except where a tree or woody shrub occurred in the central area. In this case the quadrat was placed in a predetermined corner of the subplot. On the 1985 site where only 40 subplots occurred, five subplots were chosen at random and quadrats marked in a predetermined corner. Ten subplots were unavailable for sampling on 1984 site as they were being used by other workers and here a second quadrat was placed in 10 subplots to be as far from the worker’s subplots as possible. Each of the 0.5m x 0.5m quadrats was designated a, b, c or d on a systematic basis.

During early April 1985 sixty branches in the lower canopy (1-3m high) of Betula spp and twenty branches in the upper

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Successional Age (yrs)

0 - 1 1 - 2 6 - 7 7 - 1 0 6M+

Name ruderal earlysuccessional

early mid succession

late mid succession

late

Symbol R E EMS LMS L

Site = patch of land of one successional ageSerai stage = data from sites of same age summed over two years

Table 2.1 Age and nomenclature of serai stages

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canopy (5-8m high), each approximately the size of the sampling bag described in Southwood, Brown & Reader (1979), were marked with plastic tags. The upper canopy was reached by a fixed walkway 5m high. It was not possible to sample the upper canopy during 1986 so an additional 40 branches in the lower canopy were marked in April 1986.

2.2 SAMPLING

2 .2 .i. Insect Sampling

Insects were sampled from all sites once every month between May and September inclusive. The first samples were taken from the birch immediately after 50% of the trees had burst their

buds.

Samples were taken from birch with a beating bag, and all arthropods were collected from the bag in the field with an aspirator (pooter). Samples from the other sites were taken with a D-Vac suction sampler (D ietrik, 1961; Thornhill, 1978). This method has been shown to be the most efficient sampling technique for most groups of insects on non woody plants (Heikinheimo & R&atikaiven, 1962; Henderson & Whittaker, 1977; Tormala, 1982).

One D-Vac sample lasting 30 seconds was taken from each subplot on all sites at each sampling date. The subquadrat from which the sample was taken varied at each sampling date, revolving systematically, the first sample of 1985 being taken from subquadrat a, the second from b, and continuing on a rotation basis. This prevented depletion of natural insect populations, whilst providing the most comparable sample sites.

All insect samples were sorted in the laboratory as soon as possible after collection. Insects were separated from plant matter and other arthropods using an aspirator. The sorting took place in a wooden sorting hood, with a light source from behind. After sorting, insects were stored in plastic tubes in 70% alchohol, to which a drop of glycerine was added. All adult

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herbivorous insects were subsequently identified to species using a Kyowa stereoscopic microscope. Most herbivorous taxa were identified although it proved impossible to identify all larval Lepidoptera, sawfly (Hymenoptera: Symphyta) and Coleoptera to species. Certain other groups were not identified to species due to a combination of taxonomic and sampling difficulties: Aphididae, Aieyrodoidea / Coccoidea (Hemiptera; Homoptera), Thysanoptera and Lonqitarsus spp (Coleoptera: Chrysomelidae). The following keys were used to identify the herbivorous insects to species; Heteroptera (Southwood & Leston, 1959) Coleoptera (Joy, 1932), Delphacidae (Le Quesne, 1960), Cicadellidae (Le Quesne, 1956, 1969; Le Quesne & Payne, 1981) and Psyllidae (Hodkinson & White, 1979). The Silwood insect collection and certain colleagues confirmed identification as necessary.

2 .2 .ii Plant Sampling

During the 30 seconds of insect sampling, plastic markers were placed around the edge of the D-vac hood, thus marking the area sampled. A circular wire quadrat exactly the same size as the D-vac sampling area (0.1m2) , was placed on the area of ground sampled by the D-vac. All plants within the quadratwere identified to species using Clapham, Tutin & Warburg(1981), F itter, Fitter & Blarney (1980), Hubbard (1984) andFitter, Fitter & Farrer (1984).

All the leaves of dicotyledonous species were counted andrecorded; the tiller of monocotyledon were also counted and recorded. Estimates of the leaf area for each plant species at each sampling date were obtained by collecting leaves of plant species from each site. All plant species recorded during leaf counting were designated as either common or rare. A common plant was defined as one which was recorded in at least 20% of quadrats on the previous sampling date. A rare plant occurred in less than nine quadrats on the previous sampling date. On the first sampling date of the season, the designation of common and rare was made on that month's leaf count. On each site a leaf of a common dicotyledon plant was collected from each subplot in which it occurred. The leaves were chosen by

49

selecting the leaf/plant closest to a randomly positioned point quadrat in each subplot. When plants with a strong vertical component in their habit eg Cirsium arvense, Chamaenervon angustifolium and Pulicaria dysenterica were being sampled, the plant closest to the point quadrat was sampled and a single leaf chosen at random. This method ensured that all leaves on such a plant had a chance of being sampled, otherwise the largest leaf would always be the one closest to the point quadrat. All rare plants were sampled every other sampling date so as to avoid depletion of the natural population. Estimates for the area of a grass tiller were obtained by multiplying the mean area of a grass leaf by the mean number of leaves on a tiller. These data were obtained for a grass species on a site at a given date by selecting the tiller closest to a randomly positioned point quadrat in every subplot and recording the number of leaves on each tiller. (A leaf was defined as the area of tissue between the leaf apex and the junction of the leaf blade and leaf sheath).

All leaves were frozen within 1hr of collection at -11 °C and kept in a freezer. In 1985 leaf area was measured using an Optomax and in 1986 with an IBM compatible Digithurst Microsight I. If less than 30 leaves of a species from a site on a date had been collected then all leaves were measured for area. If more than 30 leaves had been collected from a site on one date, then a subsample of 30 leaves was randomly chosen for areameasurement.

When no data were available for the leaf area of a species on a site on a given date, then data obtained at the next sampling date were used as an estimate. Indeed, such estimates of leaf area were frequently used for "rare" plant species. When data were completely lacking for a species on a particular site, data from the next oldest site were used as an estimate. Thisoccurred very rarely when a species was represented by only one individual which could not be found for leaf area analysis.

Immediately after sampling a branch of birch for insects the number of leaves sampled was counted. Leaves for area analysis were collected randomly from upper canopy and lower canopy in 1985 at each date, and only from the lower canopy in 1986.

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2.3 DATA HANDLING AND ANALYSIS

2.3 .i Rationale behind database

Absolute abundance is defined as the number of individuals of a species per unit resource of host plant. The resource used here is host plant leaf area. The information on a species' host plant is available in the literature. However, the reliability of these data varies both within and between insect orders. In order to make best use of the available data, but not be solely dependent on potentially unreliable data, two measures of absolute

abundance were calculated, one using the host plant species, if specified in the literature, and a second using the host plant's family. The latter, absolute abundance by host plant family (abhf) is calculated as:

_ number adult insects in sp ytotal leaf area of host plant's family(m2)

This measure of absolute abundance allows for literature records of species found feeding on only one plant species to be unreliable. It is particularly useful for species which may feed on more than one species in a genus or family, e.g among the weevils Apion aethiops feeds on Vicia spp, Apion assimile on Trifolium spp, Apion hydrolopathi on Rumex spp, Sitona hispidulus on Leguminosae (Hyman, 1983), in the Cicadellidae and Delphacidae which may be associated with one grass species but may feed on others, e .g . Arthaldeus pascuellus feeds on grasses (Ossiannilsson, 1983) especially Agrostis capillaris(Waloff & Solomon, 1973), Elymana sulphurella feeds on grasses (Ossiannilsson, 1983) especially Holcus (Waloff & Solomon, 1973) and also for those species for which no specific host plant is known, e .g . Agallia ribauti grasses (Le Quesne, 1965) and Aphrodes bifasciatus on grasses (Le Quesne, 1965).

The other measure of absolute abundance, absolute abundance by host plant species (abhs) is calculated as:

number adult insects in sp yabhsleaf area of host plant of sp y(m2 )

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This measure of absolute abundance is only as reliable as host plant records. If an insect species is recorded as having more than one host plant and both were present in a plot, then the sum of their leaf area was taken. These measures assume no difference in the insect's preference for host plants. Little data was available on host plant preferences of oligophagous species, and if they were, such data would be difficult to assimilate into the measure of absolute abundance. If no known host plant is recorded for a species is was assumed to be an absolute generalist, e .g . Stygnocoris pedestris (Heteroptera); in this case the denominator in the equation for absolute abundance was the total leaf area on that date/site. If a species had a host plant record but the host plant was not recorded on the sites, then absolute abundance was assigned a missing value and excluded from analyses.

Only adult insects were used in estimating absolute abundance for two reasons. Firstly, it is generally very difficult to identify immature stages of insects to species level and such identification to species is imperative in order to determine the host plant. Secondly, absolute abundances of species could vary within their lifecycle and, in order to render absolute abundance comparable, only one lifecycle stage should be considered.

A database was constructed on an Amstrad PC1512 HD20 using the "STATISTIX" statistical package (NH Analytical Software USA). In this, the number of nymphs and adults of each species on a subplot on each sampling date was recorded for each site. The leaf area of the insects host plant family and its host plant species (if present) on that subplot was also recorded. Simply,

absolute - num^er ° f adult individuals in sp y on subplot x abundance host plant leaf area on subplot x(m2)

this would be the absolute abundance for each plot. However, unexploited host plants were recorded - that is, a given species of insect did not occur on all patches of its potential host plant(s). These patches were assumed to be available for

52

exploitation, however, and should therefore be included in the analysis of absolute abundance. The resulting equation if number of individuals = 0 is clearly nonsensical. Thus, in order to get around the problem, absolute abundance was calculated at the site level.

akak _ number of adult individuals in sp y on site xhost plant leaf area on site xim 2)

2 .3 .ii Distribution of the data

The absolute abundance of insect species is not distributed normally, being highly skewed towards low values. Common statistical transformations failed to normalise the data. The distribution of absolute abundance accurately reflects the natural situation as it implies that most herbivorous insects are uncommon relative to their host plants, although some are extremely common. This pattern has been recorded in several communities (Lawton & McNeill, 1979; Strong, Lawton &Southwood, 1984).

Before statistical analysis may be undertaken it is usual to specify a mathematical function that fits the distribution of the data, e .g . normal, Poisson, binomial. Such a function may be reached by one or two methods. Firstly, it may be assumed for good biological reasons that the data will approximate to a certain distribution. Secondly the distribution of the data may be tested against various functions in order to determine the closeness of fit to the data. Due to the non-normality of the data, the second approach to distribution fitting was adopted.

2 .3 .iii Gamma distribution

The form of the data suggested that it might follow a gamma distribution. There is a constant coefficient of variation in gamma distribution (a normal distribution has constant variance).

If coefficient variation (SD)x

k

SD = standard deviation x = mean

k = a constant

then x = SD.k

It is therefore possible to test a data set in order to determine whether it follows a gamma distribution by plotting the coefficient of variation against the mean, or by plotting the mean against standard deviation and fitting a line by linear regression. In the former case, the slope of the fitted line must not be significantly different from zero, and in the second the fitted line must be significantly greater than zero and pass through the origin. The database was tested by insect group in order to determine whether it followed a gamma distribution. It is possible to analyse data with gamma errors by using Generalised Linear Interactive Modelling (GLIM) (Royal Statistical Society 1986).

2 .3 .iv Generalised linear interactive models (GLIM)

Simply, GLIM is a method for fitting statistical models by maximum likelihood. According to McCullagh & Nelder(1985) "Fitting a model to data may be regarded as a way of replacing a set of data values y by a set of fitted values p derived from a model involving (usually) a relatively small number of parameters. In general, the ps will not equal the ys exactly and the question then arises of how discrepant they are, because while a small discrepancy may be tolerable a large discrepancy is not. Measures of discrepancy (or goodness of fit) may be formed in various ways, but we shall be primarily concerned with that formed from the logarithm of a ratio of likelihoods to be called the deviance".

The analysis of deviance is the GLIM equivalent to analysis of variance. "The terms in the analysis of variance can usefully be

54

thought of as the first differences of the goodness of fit statistic for a sequence of models, each including one term more than the previous one. Thus the factorial model for two factors A and B gives rise to an analysis of variance with three terms, A, B and

A .B . The sums of squares for these are the first differences of the residual sums of squares obtained from fitting successively the models 1, A, A + B and A + B + A .B . As an example consider the following analysis of an unreplicated 4 x 3 table indexed by A and B (see Table 2 .2 ).

On the left is the sequence of models with their discrepancies, as measured by the residual sums of squares: note that the last model is the full model, i.e . has as many parameters as observations, so the degrees of freedom (df) and the discrepancy are both zero. On the right is the analysis-of-variance (anova) table, with the sums of squares (s .s .) obtained from the first differences of the discrepancies. Note that the discrepancy for model 1 is just the total sum of squares about the mean in the anova table. The form of thegeneralisation is now clear. Given a sequence of nested models we can use the deviance as our generalised measure of discrepancy and form our analysis of deviance (anodev) table by taking the first differences" McCullagh & Nelder (1985). When gamma distribution is specified, the change in deviance between successive models is checked for significance in F tables as in standard ANOVA.

One important point about GLIM is that although standarddistributions are referred to such as normal, binomial, Poisson or gamma, the principal conclusions depend only on second- moment assumptions, rather than on the correctness of theassumed distributional form, that is on the variance to mean relationship and uncorrelatedness. "This is fortunate because one can rarely be confident that the assumed distributional form is necessarily correct" (McCullagh S Nelder, 1985).

Standard error bars with gamma distribution are asymmetric.

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Model df DiscrepancyAnalysis ss df

of Variance Term

1 11 1000400 3 A ingnoring B

A 3 600200 2 B eliminating A

A + B 6 400400 6 A.B eliminating

A + B + A. B 0 0 A and B

Table 2.2

Model analysis of deviance table for two-way analysis of deviance (ANODEV) (taken from

McCullagh & Nelder, 1985).

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2 .3 .v Other statistics

Where appropriate, non-parametric statistical tests are employed. Although non-parametric tests are considered less powerful than their equivalent parametric tests, if the assumption underlying parametric statistical analysis are in some way violated, then they are more powerful. One problem with two of the most frequently used non-parametric tests, Mann Whitney-U test and the Kruskall-Wallis test, is that they actually compare the distribution of the data and not the means. They are, however, frequently treated as tests for differences between means (Zar, 1984). The power efficiency of the Mann Whitney-U test and Kruskall-Wallis test, when applied to data which may be properly analysed by the most powerful parametric tests, t-test and F-test respectively, is approximately 95% (depending on sample size) (Siegel, 1956).

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CHAPTER THREE

COMMUNITY PATTERNS THROUGH SUCCESSION

3.1 INTRODUCTION

Changes in plant diversity, species richness and stability during succession have been much studied and are well-documented (Clements 1916; Gleason 1917, Margale? 1968; Odum 1969; Drury & Nisbet 1973, Denslow 1980). Fewer studies have considered patterns in insect communities (eg VVitkowski, 1973; Itamies, 1983). Trends along a secondary successional sere at Silwood Park have been described in detail by Southwood, Brown & Reader (1979), Brown (1982a, 1982b, 1984-, 1985) and Brown & Hyman (1986). Major conclusions from these studies have shown that community stability, plant structure and architecture increase with successional age, although plant diversity peaked in early succession (Southwood, Brown & Reader, 1979). These community attributes are associated with the change from communities of annual herbs to those dominated by grasses and perennial herbs, and finally to woodland. Studies on insects have showed that the abundance of chewing and sap-feeding herbivores, and parasitoids and predators increase during succession (Brown S Southwood, 1987). Diversity of phytophagous and predatory insects peaked in early succession, mirroring that of plant diversity (Southwood, Brown & Reader, 1979). Community analysis suggested that guild structure was not constant between serai stages: the proportion of sap­feeding insects decreased with successional age, while that of tourists, predators and parasitoids increased (Brown & Southwood, 1983). It has also been observed that the life history strategies of insects varied during succession with the herbivorous species colonising ruderal sites having shorter generation times, wider feeding niches and higher reproductive potential than insects of later stages (Brown & Southwood, 1987).

This chapter aims to describe the plant and insect herbivore communities along the Silwood successional gradient during the

58

two years of the study. It is not intended as an in-depth community analysis, but as background information on the patterns and abundance of plants and herbivores through succession. Such information will allow greater understanding of hypotheses tested later in this thesis. The chapter has two major sections; one describing the plant and one the insect community. The former compares the species composition of communities between years on sites of the same age and between serai stages of different age. Similarly, species composition between years and stages is considered for major plant families. As leaf area is the resource used to obtain a measure of absolute abundance, it is relevant to consider changes in leaf area within and between serai stages of the whole community and of major plant families. Annual variation within and between serai stages of leaf area is examined. May (1975) suggested that allmeaningful ecological information about diversity could be gained by examining species richness and the extent to which the community is dominated by certain species. This method wasemployed to give some insight into plant diversity. Dominance of a community by a species was calculated by consideringcontribution to the community's leaf area.

Similar analyses were carried out for the insect community;variation between years and serai stages in abundance and species richness of the whole herbivorous insect community and each major insect group were considered. The similarity in the species composition of the major insect groups between years and serai stages gave some information on the turnover rates of herbivore species through succession. Due to the different sampling methods employed on birch, some aspects of its insect community were analysed separately. Species richness and the structure of the insect community was compared between upper and lower canopy and between years. The abundance of a single very common genus of sap-feeder on birch, Oncopsis, was also considered. The genus Oncopsis (Cicadellidae) is taxonomically very difficult; six species are known to feed on trees in Britain (Claridge, Reynolds S Wilson, 1977). Discrimination between species on purely morphological grounds is difficult, the genitalia provide the most useful characters

5 9

(Claridge & Nixon, 1981). Analysis of male courtship songs suggests the existence of further sibling species similar to 0 . flavicollis (Claridge & Reynolds, 1973), which are as yet indiscriminate from flavicollis on purely morphologicalcharacters. Due to the confusion over the taxonomy of this genus, and the difficulty in their identification only one species was recognised throughout the analysis. However, in order to provide some information on the abundance of different species in the genus between canopies and dates, subsamples were taken at random, dissected and identified to species using the RESL Handbook.

3.2 METHODS

General field methods are described in Chapter 2. Extensive use of regression analysis was employed in order to determine the slope of the fitted line describing various relationships. P values quoted after regression equations refer to the significance of the difference of the slope of the fitted line from zero. Non parametric tests were employed where the data did not comply with the assumptions of a normal distribution tested by Bartlett's test of inequality of variances and/or the Wilts-Shapiro test. The Kolmogorov-Smirnoff test was used to test for differences between distributions. Although it is a powerful test, the small number of data points decrease its sensitivity, and it will act conservatively.

The similarity of species composition between communities was described by Sorensons Index of Similarity (see Southwood, 1978).

Cs = 2]i a T b )

where j = number of species common to the two samples and a and b are the total number of species in each sample. Cs (the similarity coefficient) may vary between zero and one, zero if there are no species common to both samples, and one if all species are common. This index does not take abundance into

6 0

consideration and therefore gives equal weight to rare and common species. It is, however, appropriate for the comparison of species richness.

The dominance of a plant community by a species (P ^ was calculated by

P.j = leaf area of dominant species total leaf area

P.j was calculated for the dominant species in the community and for each of the five major families on each date, and over all dates for each serai stage in both years.

The insect community on birch was analysed separately; comparisons were made between upper and lower canopy 1985 and between the lower canopy 1985 and 1986. Due to the different sample sizes in the years and canopies the communities were not directly comparable. There were also temporal differences between the 1985 and 1986 data; sampling commenced on birch when approximately half the trees had burst their buds, this occurred on April 18, 1985 and on May 5, 1986. The regime of one sample per month thus led to six samples being taken in 1985 and five in 1986. Comparisons between years were made by pairing the first sample of each year and so on through the year. This leads to the sample taken in September 1985 having no equivalent sample in 1986. This method of comparison was deemed preferable to one pairing samples by calendar month, as it should be more biologically meaningful.

3.3 RESULTS

3 .3 . a Plant Community

3 .3 . a.i Plant species composition

Plant species richness was greatest on the early midsuccessional site in 1985 and least on the ruderal site in 1985 (Fig. 3 .1 ). There was no effect of year of sampling on plant species

Number of plant species recorded in each of two years on ruderal (R ), early (E ), early mid (EMS) and late mid (LMS) successional sites.

Number of plant species recorded on four serai stages by summing two sites of the same age (ruderal (R ), early (E ), early mid (EMS), late mid (LMS)).

SERAL STAGE

PLANT SPECIES RICHNESS PLANT SPECIES RICHNESSFIG

3.1

Fig 3.3 Number of plant species recorded in each of the major plant families during 1985 and 1986 on sites of different successionai age, ((a) ruderal, (b) early, (c) early mid, (d) late midsuccession; mf = minor families; Leg = Leguminosae, Co = Compositae, Cr = Cruciferae, Po = Polygonaceae, Cr = Gramineae).

NUMB

ER O

F SPE

CIES

61

FIG 3.3

c)EARLY MED SUCCESSION d)LATE MIDSUCCESSION

PLANT FAMILY

I I 1985 n ~ n 1986

6 2

richness (t = 0.25, df = 6, P = 0.81). Plant species richness increased with successional age until early midsuccession, when 67 species were recorded, and then declined to 52 in late midsuccession (Fig 3 .2 ). Species richness in each major plant family was similar between years within each serai stage (Fig. 3.3a - d ). Species richness on the ruderal serai stage was not significantly different between years (X2 = 1.62, df = 5, P = 0.89). The species richness of Gramineae and of minor plant families in early succession was greater in 1985 than 1986, with 15 more species belonging to minor plant families being recorded in 1985 than 1986. However, there was no significant difference in total species richness between years CX2 = 3.859, df = 5, P = 0.569). Neither were there any significant differences in total species richness between years in either of the midsuccessional serai stages (EMS, X 2 = 1.94, df = 5, P = 0.8574; LMS, X? = 1.122, df = 4, P = 0.89), with the largest difference between years occurring in the minor plant families.

Seasonal trends in plant species richness can be seen in Fig.3.4. Species richness in the ruderal serai stage increased throughout the season in 1985 and 1986 but the trend was not significant (1985, species richness = 17.4 + 1.6 date, P = 0.09; 1986, species richness = 23.1 + 1.9 date, P = 0 .3 ). In contrast in early succession, the number of plant species recorded decreased slightly throughout the year in both years (1985, species richness = 21.0 - 0.2 date, P = 0.55; 1986, species richness = 34.0 - 0.6 date, P = 0.25) (Fig. 3 .4b). In the early midsuccessional site plant species richness increased throughout the year, and was significant in 1985 (1985, species richness =22.4 + 1.6 date, P < 0.05; 1986, species richness = 28.3 + 1.7 date, P = 0.77). In the late midsuccessional site species richness decreased in both years (1985, species richness = 30.6 - 1.6 date, P = 0.125; 1986, species richness = 31 - 0.4 date, P = 0.4075). With the exception of early succession, more plant species were recorded in 1986 than 1985.

There was greater constancy in plant species composition between years with increasing age of the community, with that of the two midsuccessional serai stages being most similar between

Fig 3.4 Number of plant species recorded on each date during 1985 and 1986 on sites of different successional age ((a ) ruderal, (b) early, (c) early mid, (d) late midsuccession).

SPEC

IES R

ICHN

ESS

63

FIG 3.4

a)RUDERAL________________ b)EARLY SUCCESSION40 -

33 - 33 • + ♦■ ■JO - ■ 30 - ♦

23 - + + 23 -♦ ■20 - ■ 20 - ■ ■ ■ ■

♦13 - 13 -

10 - 10 -3 - 3 -

MAY JUNE JULY AU<J SEPT MAY JUNH JULY AUO SEPT

c)EARLY MIDSUCCESSION«33

30

13

20

13 10

3

0

d)LATE MIDSUCCESSION

MAY JUNE JULY AUd

DATE+ 1985

■ 1986

64

Serai Stage

Plant Family Ruderai Early Early mid Late mid

Minor families 0.25 0.41 0.65 0.82

Leguminosae 0.50 0.77 0.93 0.71

Compositae 0.70 0.63 0.75 0.67

Cruciferae 0.67 - - -

Polygonaceae 0.83 0.33 1.00 0.50

Gramineae 0.50 0.80 0.92 0.90

Overall 0.56 0.56 0.79 0.78

Table 3.1 Sorensons Index of Similarity for plant species in each major plant family between years in different serai stages.

6 5

years (Table 3 .1 ). Plant species in the Polygonaceae showed least variation between years in the ruderal serai stage and Leguminosae and Gramineae the most. In contrast, these latter two families showed least variation between years in the early serai stage and Polygonaceae the most. A similar pattern occurred in early midsuccession where species of Leguminosae and Gramineae remained fairly constant between years, however, the same three species of Polygonaceae, Rumex acetosella, R. acetosa and R^ crispus occurred in both years. In the late midsuccessional serai stage Polygonaceae were the most variable, and again Leguminosae and Gramineae the most stable of the

major families. The species composition of the minor families was also similar between years in this serai stage.

3 .3 .a . ii Leaf area and the plant community

Total leaf area

Total leaf area displayed a distinct successional pattern, with increases occurring from ruderal to early midsuccession and from midsuccession to late succession. There were, however, no significant differences in leaf area between serai stages (Kruskall-Wallis = 0.8957, P = 0.83) or between years on any serai stages (Kruskall Wallis = 4 .1 , P = 0.7584) (Fig. 3 .5 ). The greatest leaf area sampled was in late succession, these data were not included in the analysis as the sampling method was not comparable with that on the other serai stages.

Annual fluctuations in leaf area in a serai stage

Total leaf area of the ruderal serai stage was generally greater in 1985 than 1986, but the difference was not significant (t (unequal variances) = 0.38, d f = 4,4 , P = 0.72). In 1985 leaf area increased significantly with date (Fig. 3.6) (leaf area =

9659 3 date — 6543.8 , P < 0 .01 ), whereas in 1986 the slope ofZlthe fitted line was negative (leaf area = 2.236 x 10 - 888.75date, P = 0.5155 (Fig. 3 .6 ). The high value for leaf area in May 1986 was due to Chenopodium album which did not occur in 1985. The increase in leaf area during July and August 1985

Fig 3.5 Total leaf area on serai stages of different successional age, data summed over two years (R = ruderal, E = early, EMS = early mid, LMS = late mid, L = late succession).

6 6

FIG 3.5400 -r

C\JE

^0) 350 -

" i'oCO

300 -

'oi-HXI250 -

| 200 -

150 -

1 100 -

50 -

0 -■EMS LMS

SERAL STAGE

6 7

w as m a in ly as a r e s u l t o f th e g r a s s e s w h ic h w e re n o t p r e s e n t in

s u c h a b u n d a n c e in 1986. In th e e a r ly s u c c e s s io n a l s i t e s t h e r e

w as a s i g n i f i c a n t d i f f e r e n c e in to ta l le a f a re a b e tw e e n y e a r s (t =

2 .6 1 , d f = 8 , P = 0 .0 3 ) w ith th e h i g h e r v a lu e s o c c u r r i n g in

1985. L e a f a re a d e c r e a s e d s i g n i f i c a n t l y t h r o u g h th e y e a r in b o th

y e a r s (1985 , le a f a r e a = 3 .1 5 8 x 104 - 3214 .4 d a t e , P = 0 .0 1 ;

1986 le a f a re a = 5r623 x 104 - 6646.1 d a t e , P < 0 . 0 5 ) . L e a f a r e a

s h o w e d a s im i la r s e a s o n a l t r e n d in b o th y e a r s in th e m id -

s u c c e s s io n a l s i t e s . L e a f a re a p e a k e d in A u g u s t in b o th s i te s a n d

y e a r s , a l t h o u g h th e p e a k w as le s s p r o n o u n c e d in 1986. T h e r e

w e re s i g n i f i c a n t d i f f e r e n c e s in to ta l le a f a r e a b e tw e e n y e a r s on

b o th s i te s ( E M S , t = 3 . 4 4 , d f = 8 , P < 0 .0 1 ; L M S , t = 4 . 3 6 , d f =

8 , P < 0 . 0 1 ) . H o w e v e r , in e a r l y m id s u c c e s s io n in 1985 th e s lo p e

o f th e f i t t e d l in e w as n e g a t i v e , w h e r e a s in 1986 a n d in b o th

y e a r s in la te m id s u c c e s s io n le a f a re a te n d e d to in c r e a s e t h r o u g h

th e y e a r (E M S 1985, le a f a re a = 3 .9 5 9 x 104 - 9 8 5 .9 2 d a t e , P =

0 .6 9 9 ; 1986, le a f a r e a = 2.461 x 104 + 3 8 1 .4 d a t e , P = 0 .7 1 6 ;

L M S 1985, le a f a re a = 3.201 x 104 + 1140.1 d a t e , P = 0 .6 2 6 ; 1986

le a f a re a = 2.21 x 104 -+- 5 3 4 .1 3 d a t e , P = 0 .6 5 2 ) .

T h e le a f a r e a o f b i r c h , e x p r e s s e d a s th e m ean le a f a r e a p e r b a g ,

d i s p l a y e d c l e a r s e a s o n a l t r e n d s ( F i g . 3 . 7 ) . M ean le a f a r e a p e r

b a g o f b i r c h o n lo w e r c a n o p y 1985 in c r e a s e d u n t i l J u n e a n d t h e n

g r a d u a l l y d e c l i n e d u n t i l th e e n d o f th e y e a r . In 1986 m ean le a f

a re a p e r b a g i n c r e a s e d f r o m M a y to A u g u s t a n d fe l l b y

S e p t e m b e r . T h e g r e a t e s t le a f a r e a p e r b a g on th e u p p e r c a n o p y

w as o b s e r v e d in J u l y , le a f a r e a th e n d e c l in e d u n t i l S e p t e m b e r .

T h e r e w e re s i g n i f i c a n t d i f f e r e n c e s in m ean le a f a r e a p e r b a g

b e tw e e n d a t e s f o r a l l c a n o p ie s ( L C 1985, K r u s k a l i - W a l l i s =

1 0 4 .3 7 , P < 0 .0 0 1 ; U C 1985, K r u s k a l l - W a l l i s = 3 7 .4 7 7 , P < 0 .0 0 1 ,

L C 1986, K r u s k a l l - W a l l i s = 1 5 3 .3 3 , P < 0 .0 0 1 ) . T h e r e l a t i o n s h i p

b e tw e e n m ean le a f a r e a p e r b a g a n d d a te d id n o t d i f f e r

s i g n i f i c a n t l y b e tw e e n u p p e r a n d lo w e r c a n o p y in 1985

( K o l m o g r o v - S m i r n o f f = 0 .1 7 , P = 0 .9 9 ) o r b e tw e e n lo w e r c a n o p ie s

in 1985 a n d 1986 ( K o l m o g r o v - S m i r n o f f = 0 .3 0 , P = 0 . 1 9 ) .

Fig 3. L e a f a r e a r e c o r d e d on s i t e s o f d i f f e r e n t s u c c e s s io n a l

a g e a t m o n th ly i n t e r v a l s o v e r tw o y e a r s .

LEAF

ARE

A xlO

~3 (c

m2) /4

-5m2

6 8

FIG 3.6

a)RUDERAL bYEARLY SUCCESSION+•+ 40 -

• ■■

- 30 - ■

■ ■20 -

* + ♦■■ + 4- "

+♦

+MAY JUNE JULY AUO SEPT

10 -

DATE+ 1985

■ 1986

Fig 3. M e a n le a f a re a p e r b a g a t m o n t h ly i n t e r v a ls on u p p e r

a n d lo w e r c a n o p y b i r c h 1985 a n d lo w e r c a n o p y b i r c h

1986.

69

FIG 3.7

LOWER CANOPY 1985 UPPER CANOPY 1985 LOWER CANOPY 1986DATE

APRIL GHHD MAY JUNE

I I JULY EZ3 aug l i i i l sept

70

T r e n d s in th e le a f a r e a o f m ajor p la n t fa m il ie s w ith in a n d

b e tw e e n s e r a i s t a g e s

D i f f e r e n t s u c c e s s io n a l t r e n d s in to ta l lea f a re a w e re se e n in th e

m ajor p la n t ta x a ( F i g . 3 . 8 ) . In th e L e g u m in o s a e le a f a re a w as

g r e a t e s t in th e e a r l y s e r a i s t a g e a n d lea st on late m id s u c c e s s io n

( F i g . 3 . 8 a ) . T h e r e w e r e s i g n i f i c a n t d i f f e r e n c e s in le a f a re a

b e tw e e n s e r a i s t a g e s ( K r u s k a l l - W a l l i s = 1 6 .5 3 9 , P < 0 .0 0 1 ) b u t

n o t b e tw e e n y e a r s w i th in a s e r a i s t a g e . T h e r e w e r e no

s i g n i f i c a n t d i f f e r e n c e s in le a f a r e a o f C o m p o s ita e b e tw e e n s e r a i

s t a g e s ( K r u s k a l l - W a l l i s = 4 .4 4 , P = 0 .2 2 ) o r b e tw e e n y e a r s w i th in

a s e r a i s t a g e . T h e g r e a t e s t le a f a re a o f C o m p o s ita e w as

r e c o r d e d d u r i n g e a r l y m id s u c c e s s io n ( F i g . 3 . 8 b ) . T h e le a f a re a

o f C r u c i f e r a e d e c l in e d s h a r p l y w ith in c r e a s in g s u c c e s s io n a l a g e ,

w ith th e fa m ily n o t b e in g r e p r e s e n t e d d u r i n g late m id s u c c e s s io n

( F i g . 3 . 8 c ) . D i f f e r e n c e s in le a f a re a b e tw e e n s e r a i s t a g e s on

w h ic h C r u c i f e r a e o c c u r r e d w e re s i g n i f i c a n t l y d i f f e r e n t

( K r u s k a l l - W a l l i s = 1 8 . 1 8 , P < 0 .0 0 1 ) , a l t h o u g h d i f f e r e n c e s

b e tw e e n y e a r s w ith in a s e r a i s t a g e w e re n o n s i g n i f i c a n t . L e a f

a r e a o f P o ly g o n a c e a e d e c l i n e d from r u d e r a l to e a r l y

m id s u c c e s s io n , b u t t h e n in c r e a s e d s l i g h t l y to la te m id s u c c e s s io n

( F i g . 3 . 8 d ) . In t h i s f a m i ly , t h e le a f a re a in e a r l y s u c c e s s i o n in

1986 w as s i g n i f i c a n t l y g r e a t e r th a n in 1985 ( K r u s k a l l - W a l l i s

s t a t i s t i c = 2 3 . 9 5 , P < 0 . 0 1 ) , n o o t h e r s i g n i f i c a n t d i f f e r e n c e s

b e tw e e n y e a r s o c c u r r e d . T h e le a f a re a o f g r a s s e s w as le a s t

d u r i n g th e r u d e r a l s t a g e o f s u c c e s s i o n a n d g r e a t e s t d u r i n g e a r l y

m id s u c c e s s io n ( F i g . 3 . 8 e ) a n d d i f f e r e d s i g n i f i c a n t l y b e tw e e n

s e r a i s t a g e s ( K r u s k a l l - W a l i i s = 1 5 . 9 6 4 4 , P < 0 . 0 1 ) . T h e r e w e re

n o s i g n i f i c a n t d i f f e r e n c e s b e t w e e n y e a r s w ith in a s e r a i s t a g e .

N o c o n s i s t e n t t r e n d s in le a f a r e a o f s p e c ie s in m in o r fa m il ie s

a p p e a r e d t h r o u g h s u c c e s s io n ( F i g . 3 . 8 f ) . T h e a r e a p r o v i d e d b y

m in o r fa m il ie s w as g r e a t e s t in la te m id s u c c e s s io n , p r o b a b l y d u e

to E p i lo b iu m s p p , C h a m a e rv e r io n a n g u s t i f o l iu m a n d R u b u s

f r u t i c o s u s a g g , a n d w a s a ls o h i g h on th e r u d e r a l s i t e s , d u e

m a in ly to th e a b u n d a n c e o f S p e r g u l a a r v e n s i s . T h e r e w e r e no

s i g n i f i c a n t d i f f e r e n c e s in le a f a r e a o f m in o r fa m il ie s b e tw e e n s e r a i

s t a g e s ( K r u s k a l l - W a l l i s = 0 .8 9 5 7 , P = 0 .8 2 6 ) o r b e tw e e n y e a r s

w ith in a s e r a i s t a g e ( K r u s k a l l - W a l l i s = 4 . 1 8 4 , P = 0 . 7 6 0 ) .

F ig 3 . 8 L e a f a r e a o f (a) L e g u m in o s a e , (b ) C o m p o s i t a e , (c)

C r u c i f e r a e , (d ) P o iy g o n a c e a e , (e) G r a m in a e , ( f) m in o r

fa m i l ie s on s e r a i s t a g e s o f d i f f e r e n t s u c c e s s io n a l a g e s .

D a ta p o o le d o v e r two y e a r s . ( R = r u d e r a l , E = e a r l y ,

E M S = e a r l y m id s u c c e s s io n , L M S = ia te m id s u c c e s s io n ) .

71

c\jE0)ao

a

FIG 3.8

SERAL STAGEFIG 3.8

o>

SERAL STAGE

72

FIG 3.8CMECDCM6O

9

CMECD

CMao

a

SERAL STAGE

73

FIG 3.8

c\]E05OJ8o

s

SERAL STAGE

C\JE

05

8O

9

f)MINOR FAMILIES

SERAL STAGE

74

Contribution of the plant families to the total leaf area of a serai stage

In the ruderal site 1985, Leguminosae and grasses were the dominant contributors to leaf area and increased in importance during the first two years of succession (Figs. 3 .9a). Compositae showed a similar increase although their overall contribution to leaf area was lower. Cruciferae and Polygonaceae made relatively minor contributions and were more important during the first year of succession. In 1986 the ruderal site showed the same general trends, although the Compositae, Polygonaceae and Cruciferae made greater contributions to community leaf area than in 1985 (Fig. 3 .9b). The leaf area of grasses and minor families in early succession was greater in1985 than in 1986 but the contribution of Leguminosae to the total leaf area was lower (Fig. 3.9c&d). The proportion of total leaf area provided by the major plant families was similar on the midsuccessional sites where both commuryties were dominated by grasses, with Compositae and minor families making important contributions to the sites leaf area (Figs. 3 .9e-h ). Leguminosae, Cruciferae and Polygonaceae made very little contribution to leaf area on either site. The proportion of total leaf area provided by the major plant families was comparable between years on both sites.

Contribution of individual plant species to the total leaf area of a serai stage

The dominant plant species on the ruderal site in 1985 in terms of leaf area for the whole season was Holcus lanatus. However, during May and June Spergula arvensis was the dominant species while Trifolium pratense dominated in August (Table 3.2a). In1986 another grass species, Agrostis stolonifera was the season dominant on the ruderal site, although the annual herbs Chenopodium album and Spergula arvensis dominated the community early in the year, and a late germinating annual,

Fig 3.9 Proportion of total leaf area provided by major plant families on serai stages of different successional age. (a) ruderal 1985, (b) ruderal 1986, (c) early 1985,(d) early 1986, (e) early mid 1985, (f) early mid 1986, (g) late mid 1985, (h) late midsuccession 1986.

75

a)RUDERAL 1985FIG 3.9

MAY JUNE JULY AUG SEPT

LEGUMINOSAE CRUCIFERAE COMPOSITAE

«

POLYGONACEAE GRAMINAE MINOR FAMILIES

PROP

ORTIO

N OFT

OTAL

LEAF

AREA

76

FIG 3.9

i).9J.8

0.7

0.6

0.3

0.4

0.3

0.20.1

0

d)EARLY SUCCESSION 1986

DATE

LEGUMINOSAE CRUCIFERAE c o m p o s it a e

POLYGONACEAE GRAMINAE MINOR FAMILIES

PROP

ORTIO

N OFT

OTAL

LEAF

AREA

77

FIG 3.9e)EARLY MIDSUCCESSION 1985

MAY JUNE JULY AUG SEPT

f)EARLY MIDSUCCESSION 1986

MAY JUNE . JULY AUG SEPT

DATE

LEGUMINOSAE CRUCIFERAE COMPOSITAE

POLYGONACEAE GRAMINAE MINOR FAMILIES

7 8

f f lhJ

§122cu

FIG 3.9g)LATE MIDSUCCESSION 1985

MAY JUNE JULY AUO SEPT

1 -1h)LATE MIDSUCCESSION 1986

MAY JUNE JUEY SEPT

DATE■ □

LEGUMINOSAE CRUCIFERAE COMPOSUAE

POLYGONACEAE GRAMINAE MINOR FAMILIES

79

Galinsoga parviflora became dominant in September (Table 3 .2b). Within the major plant families pratense was the dominant legume in 1985, whereas in 1986 T_ repens dominated. In 1986, G. parviflora was the dominant Compositae, this species did not occur in 1985 and Hypochaeris radicata contributed most to the the family's area. Raphanus raphanistrum was the only crucifer in 1985 and Polygonum persicaria was the dominantrepresentative of the Polygonaceae.

In the early successional site in 1985, Agrostis stolonifera was the dominant species over the whole season, and apart from early in the year it was the dominant species in each monthly sample (Table 3.2c). However, in 1986 a herb, T^ pratense was the overall dominant species, and dominated monthly samples in June and July (Table 3 .2d ), with Holcus lanatus dominant in May, August and September. Within individual families,T . repens was the dominant legume in 1985 and T^ pratense in 1986. The dominant species in the Compositae also differed between years, with radicata dominant throughout the season in 1985, and a series of species in 1986. Within the Polygonaceae, Rumex obtusifolius and Rumex crispus dominated in 1985, and either Rumex acetosa or F\_ persicaria in 1986.

In midsuccession the grasses were the dominant species. In early midsuccession in 1985 lanatus was dominant, although this species never became dominant in 1986 and the thistle Cirsium arvense assumed dominance (Table 3.2e & f ). As inruderal and early succession the dominant legume varied between years, vAVjq. dominated the family in 1985 and Lotusuliginosus in 1986. Compositae were more similar between years, with either arvense or Senecio jacobaeae dominating on all dates. However, C^ arvense was the overall dominant for the family in both years. No Cruciferae were recorded in 1985, and only FU raphanistrum in 1986. In the Polygonaceae, R j_ crispus was only recorded in 1986 when it dominated the family, while in 1985 R^ acetosa was dominant. The dominant grass species differed between years, H^ lanatus dominated in 1985 and Dactylis glomerata in 1986. The monthly samples in 1985 from June to September were dominated by Holcus lanatus, whereas in1986 P,*ve species dominated in different months.

Table 3.2 Proportion of leaf area provided by the dominant species to the community and major plant families on each date (P^). (a) ruderal 1985, (b) ruderal 1986, (c) early 1985, (d) early 1986, (e) early mid 1985, (f) early mid 1986, (g) late mid 1985, (h) late mid 1986, and species richness (sp. no.) of each plant family and community. (Leg = Leguminosae, Co = Compositae, Cr = Crucifer, Pol = Polygonaceae, Gr = Craminae).

8 0

Tahiti 3.2.1

DATEMay June Ju ly August September Overall

f-'amily Pj sp. no. Pj sp. no. Pj sp. no. Pj sp. no. Pj sp. no. Pj sp. no.

0.699 3 0.919 9 0.55 5 0.929 9 0.895 9 0.613 6U tj

T . pratense T . pratense T . hybridum T . pratensc T . pratense T . pratensc

0.698 2 0.927 5 0.806 3 0.53 9 0.659 6 0.559 6Co

T . inodoruin C. cap illa ris C. cap illa ris T . inodorum H. radicata II. radicata

- 0 1.0 3 0 1.0 1 - O 0Cr

R. raphinostrum R. raphinostrum

0.638 2 0.509 3 0.818 3 0.53 9 0.626 3 0.799 3Pol

P. lipathifolium P. persicaria P. persicaria P. persicaria P. persicaria P. persicaria

0.735 U 0.673 5 0.709 5 0.63 5 0.600 5 0.623 5Cr

A. stolonifera II. lanatus H. lanatus H. lanatus 11. lanatus II. lanatus

0.6099 0.296 0.239 0.355 0.301 0.159Total

S. arvensis S. arvensis II. lanatus T . pratense II. lanatus II. lanatus

Table 3. 2b

D ATEMay June August September O vera ll

Family Pj sp. no. P1 sp. no. Pj sp . no. Pj sp. no. P.j sp. no. Pj sp. no.

0.65 2 0.95 3 0.79 5 0.53 5 0.59 3 0.38 6Leg

V. cracca V . tetraspermum V. tetraspermum T . repens T . repens T . repens

0.90 9 0.922 10 0.612 8 0.97 9 0.67 9 0.96 12Co

C. arvense C. parv iflora G. parv iflo ra S. asper C. parviflora G. parv iflora

0.77 2 0.7817 2 0.80 2 1.00 1 0.99 2 0.83 2Cr

R. raphinastrum R. raphinastrum R. raphinastrum C. b-pastoris R. raphinastrum R. raphinastrum

0.58 9 0.526 6 0.685 3 0.91 9 0.91 9 0.59 7Pol

R. crispus R. obtusifo lius R. av icu la re P. persicaria P. persicaria P. persicaria

0.99 2 0.987 3 0.99 2 0.97 3 0.99 2 0.98 3Or

A . stolonifera A. stolonifera A . stolon ifera A. stolonifera A. stolonifera A . stolon ifera

0.776 20 0.35 32 0.25 30 0.19 33 0.23 29 0.211Total

C. album S. arvense S. arvense A. stolonifera G. parviflora A. sto lon ifcra

81

Table 3.2c

D ATE

Family

May

Pj sp. no.

June

Pj sp. no.

Ju ly

P.j sp . no.

August

Pj sp. no.

September

Pj sp. no.

Overall

Pj sp. no.

Ley0.329 7

M. lupilina

0.953 6

V. h irsuta

0.537 7

T . repens

0.958 5

T . repens

0.629 6

T . repens

0.303

T . rcpens

Co0.597 8

T . offic inale

0.39 7

T . inodorum

0.959 8

C. canadensis

0.297 7

C. canadensis

0.257 6

T . officinale

0.159

T . offic ina le

Cr0 0 0 0 — O - C

Po'0.10 1

R. obtusfolius

0.752 2

R. crispus

0.593 3

R. obtusfo lius

1.0 1

R. obtusfolius

1.0 1

R. obtusfolius

0.556 2

R. crispus

C r0.297 7

Poa annua

0.578 6

A . stolonifera

0.795 6

A . stolon ifera

0.722 5

A . stolonifera

0.558 5

A . stolonifera

0.589

A. stolonifera

Total0.12

T . offic inale

0.193

V. h irsuta

0.269

A. stolon ifera

0.919

A . stolonifera

0.305

A. stolonifera

0.25

A . stolonifera

Table 3.2d

D ATE

Family

May

Pj sp. no.

June

Pj sp. no.

Ju ly

P1 sp . no.

August

P 1 sp. no.

September

?! sp. no.

Overall

?! sp . no.

Leg0.782 5

T . pratense

0.85 6

T . pratense

0.91 5

T . pratense

0.83 5

T . pratense

0.89 5

T . pratense

0.85 6

T . pratense

Co0.86 C

H. radicata

0.87 9

II. radicata

0.61 3

II. radicata

0.91 5

II. radicata

0.93 5

II. radicata

0.86 8

II. radicata

Cr0 0 1.0 1

R. raphinastrum

0 0 1.0 1

R. raphinastrum

Pol0 1.00 1

R. acetosella

1.0 1

P. persicaria

0 1.0 1

R. acetoseila

O. 89 2

P. persicaria

C r0.79 6

11. lanatus

0.75 9

11. lanatus

0.63 9

II. lanatus

0.76 3

11. lanatus

0.83 9

11. lanatus

0.79 6

II. lanatus

Total0.32 20

hi. lanatus

0.38 22

T . pratense

0.90 20

T . pratense

0.28 20

H. lanatus

0.38 20

11. lanatus

0.31

T . pratense

Table 3.2e

DATE

Family

May

Pj sp. no.

June

Pj sp. no.

Ju ly

Pj sp . no.

August

Pj sp. no.

September

Pj sp. no.

Overall

Pj sp. no.

Ley0.6C S

V . sativa

0.45 6

V . sativa

0.34 7

V . sativa

0.25 7

M. lupilina

0.62 5

T . repens

0.43 7

V . sativa

Co0.51 5

C. arvense

0.48 6

C . arvense

0.60 7

C. arvense

0.59 6

C. arvensfc

0.87 5

S. jacobcae

0.65 7

C. arvense

Cr0 0 0 0 0 0

Pol0 1.0 1

R . acetosa

0.72 2

R. acetosa

1.00 1

R. acetosa

0.56 2

R. acetosella

0.83 3

R. acetosa

Or0.34 6

A . cap illa ris

0.58 5

H. lanatus

0.69 6

II. lanatus

0.77 5

II. lanatus

0.84 7

II. lanatus

0.68 7

II. lanatus

Total0.18 23

A . cap illa ris

0.28 26

H. lanatus

0.38 29

II. lanatus

0.48 28

H. lanatus

0.73 30

II. lanatus

0.19

11. lanatus

Table 3 . 2f

D ATE

Family

May

P1 sp. no.

June

P, sp. no.

July

Pj sp . no.

August

P1 sp. no.

September

P1 sp. no.

Overall

Pj sp. no.

Ley0.32 5

T . repens

0.32 4

L . u lignosus

0.43 6

V. sativa

0.74 7

L. ulignosus

0.37 5

L. ulignosus

0.33 7

L. u lignosus

Co0.42 5

S. jacobeae

0.53 4

5. jacobeae

0.68 6

C. arvense

0.77 7

C. arvense

0.71 8

C. arvense

0.50 8

C. arvense

Cr1.0 1

R. raphinastrum

0 1.0 1

R. raphinastrum

1.0 1

R. raphinastrum

— O 1.0 1

Ft. raphinastrum

Pol1.0 1

R. crispus

0.79 2

R . crispus

0.85 3

R. crispus

0.52 2

R . acetoseila

0.54 2

R. acetosa

0.83 3

R. cr ispus

C r0.47 9

D. glomerata

0.23 8

H. lanatus

0.38 10

D. glomerata

0.34 7

A . stolonifera

0.39 7

H. lanatus

0.33 11

D. glomerata

Total0.20 31

D. glomerata

0.14 29

R. repens

0.23 35

T . o ffic inale

0.22 36

A . stolonifera

0.18 36

C. arvense

0.08

D. glomerata

83

Table 3.2q

DATE

Family

May

Pj sp. no.

June

Pj sp. no.

Ju ly

Pj sp. no.

August

Pj sp. no.

Septemoer

Pj sp. no.

Ovcral l

Pj sp. no.

Leg0.72 5

V . sativa

0.62 4

V . h irsuta

0.77 4

V. h irsu ta

0.44 4

L. corniculatus

1.0 1

L. corniculatus

0.49 5

V . h irsuta

Co0.42 5

T . o ffic ina le

0.37 5

C. arvense

0.43 5

C. arvense

0.61 6

C. arvense

0.33 5

C. arvense

0.57 ]

C . arvense

Cr0 0 0 0 0 0

Pol1.0 1

R. acetosa

1.0 1

R. acetosa

0.97 2

R. acetosa

1 .0 1

R. acetosa

1.0 1

R. acetosa

0.99 !

R. acetosa

Cr0.40 ii

H. lanatus

0.54 7

II. lanatus

0.50 6

II. lanatus

0.69 7

II. lanatus

0.56 C

II. lanatus

0.65 a

II. lanatus

Total0.24 28

II. lanatus

0.31 27

H. lanatus

0.29 27

H. lanatus

0.50 27

II. lanatus

0.34 20

H . lanatus

0.34

II. lanatus

Table 3.2h

DATE

Family

May

Pj sp . no.

June

Pj sp. no.

Ju ly

Pj sp . no.

August

Pj sp. no.

September

Pj sp. no.

Overall

Pj sp. no.

Leg0.88 4

L. corn icu latus

0.88 5

L. corn icu latus

0.88 3

L. co rn icu la tus

0.54 4

L. corniculatus

0.88 3

L. corniculatus

0.83 5

L. corniculatus

Co0.61 7

C. arvense

0.52 7

C. arvensc

0.63 7

C . arvense

0.51.

C. arvense

0.51 7

C . arvense

0.6.- 8

C. arvense

Cr0 0 0 0 0 0

Pol1 .0 1

R. acetosa

1.0 1

R. acetosa

1.0 1

R . acetosa

1.0 1

R. acetosa

1.0 1

R. acetosa

1 .0 1

R. acetosa

Cr0.43 7

D. glomeratn

0.58 9

D. glomerata

0.56 G

D. glomerata

0.62 9

D. glomerata

0.57 9

D. glomcrata

0.56 11

D. glomerata

Total0.17 30

D. glomerata

0.26 31

D. glomerata

0.22 29

D. glomerata

0.39 31

D. glomerata

0.29 30

D. glomernta

0. 27

D. ylomerat;.

8 4

In both years in late midsuccession grasses v/ere dominant in every monthly sample, Holcus lanatus in 1985 and glomerata in 1986 (Table 3 .2g). The Leguminosae were dominated by Vicia spp early in 1985, but by Lotus corniculatus later in the season and throughout 1986. C. arvense was generally the dominant Compositae in both years. No Cruciferae were recorded in either year and only one member of the Polygonaceae, acetosa.

3 .3 .b . Insect Community

3 .3 . b .i. Total insect abundance during succession

Peak total and adult insect abundance occurred in early succession and was lowest on the ruderal and the latesuccessional stage (Fig. 3 .10). There were significant differences in abundance between serai stages (total,Kruskall-Wallis = 12.798, P < 0.001; adult, Kruskall-Wallis11.737, P < 0.001).

3 .3 . b .ii Abundance of major herbivore taxa associated withdifferent serai stages

The total number and number of adult Heteroptera was greatest on late midsuccession (Fig 3.11 & 3.12). This was mainly due to the abundance of the Lygaeid Ishnodemus sabuleti. Numbers of Heteroptera were low on both the ruderal and late serai stages. There was a significant difference in total Heteroptera number and number of adults between serai stages (total, Kruskall- Wallis = 26.308, P < 0.001; adult, Kruskall-Wallis = 18.97, P < 0.001). The number of Psyllidae was generally low in the early successional stages but increased in late midsuccession and on birch (Fig. 3 .11), but was higher in the former due to the broom feeding species Arytainiila spartiophila and Arytaina genistae. There was a significant difference in abundance between serai stages (Kruskall-Wallis = 14.885, P < 0.001). No

nymphal Psyllidae were recorded.

Fig 3.10 Total number of (a) adult insect herbivores(b) insect herbivore individuals (excluding Aphididae, Coccoidea,, Aleyro^oidea (Hemiptera), Thysanoptera and Lepidoptera) on serai stages of different successional age. Data summed over two years (R = ruderal, E = early, EMS = early mid, LMS = late midsuccession, L = late).

85

FIG 3.10

a)ADULT ABUNDANCE10000 -T

9000 -

w 8000 -u2 7000 -

< 6000 -Q2 5000 -

4000 -

{3 3000 -

2000 -

1000 -

o J -14000

SERAL STAGE

b)TOTAL ABUNDANCE13000 -

w 12000 -U 11000 -2 10000 -< 9000 -Q 8000 -2 7000 -D 6000 -m 5000 -< 4000 -

3000 -2000 -1000 -

SERAL STAGE

8 6

Among the Auchenorrhyncha the abundance of Cercopidae was greatest in early succession, and gradually decreased through succession (Fig. 3.11). However, no significant differences in abundance between serai stages occurred ( Kruskall-Wallis = 5.209, P = 0.267). No nymphal Cercopidae were recorded. The abundance of Delphacidae increased from ruderal to latemidsuccession, however none were recorded on birch (Figs. 3.11 & 3.12). There were significant differences in total and adult abundance of Delphacidae between serai stages (total, Kruskall- Wallis = 21 .673, P < 0.001; adult, Kruskall-Wallis = 19.0472, P < 0.001). The total number of Cicadellidae peaked in early midsuccession, with the lowest number being recorded in the ruderal stage (Figs. 3.11 & 3.12). The differences inabundance between serai stages were significant (total,Kruskall-Wallis = 19.77, P < 0.001; adult, Kruskall-Wallis =

11.269, P < 0.001).

Due to their habit, no larval Curculionoidea wererecorded; the number of adults was greatest in early succession. The differences in abundance between serai stages were significant (Kruskall-Wallis 26.102, P < 0.001). Total and adult abundance of Chrysomelidae were highest in the ruderal stage but were low on the other serai stages. No Chrysomelidae were recorded on birch. There were significant differences in total and adult abundance between serai stages (total, Kruskall-Wallis = 20.694, P < 0.001; adult, Kruskall-Wallis = 13.615, P < 0.001)(Figs. 3.11 & 3 .12). The abundance of Chrysomelidae in theruderal serai stage was due to the abundance of Cassida spp adults and nymphs which feed on Stellaria spp, Cirsium spp, Urtica spp and Sperguia arvensis.

3 .3 .b .iii Annual variation in insect abundance

Total numbers

The abundance of herbivorous insects in the ruderal stage was similar between years, peaking in August in both years (Fig. 3.13) (1985, number = 191.2 + 206 date, P = 0.149; 1986,number = -414.4 + 308 date, P < 0.05). In early succession, the pattern of abundance was different between years: in 1985

Fig 3.11 Total number of individuals in each major insect group on serai stages of different successionai age. Data pooled over two years (R = ruderal, E = early, EMS = early mid, LMS = late mid, L = late succession).

TOTA

L ABU

NDAN

CE

87

FIG 3.11a)HETEROPTERA7000 ■ *

WOO •

5000 •

4000 -

MOO - ' 1

2000 •

l coo - ------o " * 1 » I I I » 1R 8 BMO LMS L

R 8 BMi LMS l

SERAL STAGE

Fig 3.12 Total number of adults in each major insect group on serai stages of different successional age. Data pooled over two years (R = ruderal, E = early, EMS = early mid, LMS = late mid, L = late succession).

ADUL

T ABU

NDAN

CE

8 8

FIG 3.12

KB0 2SG0 - 2600 - 2400 - 2200 -

2000 -

I wo - 1600 - 1400 - 1200 - 1000 - too - 600 • 400 - _ 200 •

a)HETEROPTERA b)DELPHACIDAE

d)CHRY SOMELID AE

SERAL STAGE

89

numbers had increased to 2600 by July, then fell progressively (number = 602.7 + 135.3 date, P = 0.659), whereas in 1986 numbers increased until August then fell in September (number =365.3 + 290.7 date, P = 0.701). The seasonal pattern ofabundance was also different between years in early midsuccession. In 1985 abundance increased progressively through the season (Fig. 3.13c) (number = 377.9 + 183.3 date, P < 0.05). In 1986, however, numbers peaked in July and then declined during August and September (number = 865.9 + 6.7 date, P = 0.940). The patterns of abundance in late midsuccession were very different to those in early midsuccession (Fig. 3.13d). Abundance peaked in August in 1985 and in June in 1986 (1985, number = 656.6 + 152.4 date, P = 0.14: 1986, number = 1370.7 - 43.7 date, P = 0.876). In late succession the slope of the fitted regression line was negative for the upper and lower canopy in 1985 and the lower canopy in 1986 (LC 1985, number = 538.8 - 89.6 date, P = 0.075; UC 1985, number = 221 .2 - 24 date, P = 0.266; LC 1986, number = 601 .7 - 46.7 date, P = 0.644). Numbers peaked in June for the lower canopy 1986 and for the upper canopy 1985, and in May for the lower canopy 1985. The increased numbers on the lower canopy 1986 were probably due to the increased sampling effort.

Adult numbers

The abundance of adult insects in the monthly samples from the ruderal sites was similar in both years (number = -135.3 + 135 date, P = 0.069; number = -206.3 + 161.5 date, P < 0.05) (Fig. 3.14). Numbers were also similar in May, June and September of both years in early succession. Peak abundance switched between the two years being in July in 1985 and in August in 1986 (1985, number = 602.7 + 135.3 date; 1986, number = 365.3 +290.7 date, P = 0.701). Adult abundance increased almost linearly through 1985 in early midsuccession (number = -55.8 +182.8 date, P < 0.001). in 1986 the number of adults recorded in June, July and August were similar to those in the same months during 1985, however in contrast, numbers decreased dramatically in September 1986 (number = 220.5 + 66.5 date, P = 0.228) (Fig. 3.14c). Adult abundance in late midsuccession also

Fig 3.13 Total number of insect herbivore individuals (excluding

Aphididae, Coccoidea , Aleyro&aidea (Hemiptera\ Thysanoptera and Lepidoptera) recorded on monthly samples over two years on serai stages of different successional age.

TOTA

L ABU

NDAN

CE

9 0

FIG 3.13MOO1300120011001000

900100700600300400300200

1000

a)RUDERAL 3000 2100 2600 2400 2200

2000 1100 1600 1400 1200 1000 too 600 400 200 0

MAY JUNE JULY AUO SETT

b)EARLY SUCCESSION

l I "■ — » i i

NEARLY MIDSUCCESSION (PLATE MIDSUCCESSION

MAY JUNE JULY AUO SEPT

1000 900 too 700 600

300 400 300 200 100 0

elLATE SUCCESSION

MAY JUNE' JULr

+ 1985 ■ 1986

+ LOWER CANOPY 1985 o UPPER CANOPY 1985 ■ LOWER CANOPY 1986

DATE

Fig 3.14 Total number of adult herbivores (excluding Aphididae, Coccoidea , A ley ro bides. (Hemiptera\Thysanoptera and Lepidoptera) recorded on monthly samples over two years on serai stages of different successional age.

ADUL

T ABU

NDAN

CE

9 ]

FIG 3.14a)RUDERAL

MAY nmB JULY AUQ SETT

b)EARLY SUCCESSIONTXT}2000

taoo two 1400 1200

1000 800 <00 400 200

0MAY JUNE JULY AUO SEPT

+ 1985 1986

e)LATE SUCCESSION

+ LOWER CANOPY 1985

O UPPER CANOPY 1985

■ LOWER CANOPY 1986

m ay n j m iuly A lia sept

DATE

92

increased almost linearly from May to August 1985 (number = 75.7 + 105.5 date, P = 0.881). In 1986 adult abundance was generally higher and peak adult abundance was recorded in June, due mainly to the abundance of lshnodemus sabuleti (Hemiptera: Heteroptera) and Arytainilla spartiophila (Hemiptera: Psyllidae) (number = 734 - 29.6 date, P = 0.184). The number of adults on lower canopy birch 1985 followed the same pattern as that already described for total abundance (number = 430.6 -79.4 date, P = 0.097). However, on both lower canopy 1986 and upper canopy 1985, adult abundance was greatest in midsummer (1985 UC, number = 221 .2 - 24 date, P = 0.443; 1986 LC, number = 601 .7 - 46.7, P = 0.721).

3 .3 .b .iv Annual variation in abundance of insect groups

There were no significant differences in numbers of adults or nymphs between years on any serai stage as tested by a Mann Whitney U Test (Table 3 .3 ). However, eleven Psyllidae were recorded in the ruderal stage in 1986 and none in 1985, and 46 in early succession in 1985 and none in 1986. Similarly Chrysomelidae were recorded in early midsuccession in 1985 and not in 1986. Cicadellidae were the most abundant group in ruderal, early midsuccession and late succession but were also important on the other serai stages. Curculionoidea were numerically dominant in early succession and Heteroptera in late midsuccession. Cercopidae, Psyllidae and Chrysomelidae were less abundant in all stages, with Cercopidae being particularly rare.

3 .3 .b .v Herbivore species composition

Variation in species richness with serai stage

Insect herbivore species richness was greatest in midsuccession, and least in late' succession (Fig 3.15a). There were significant differences in species richness between serai stages (one way ANOVA, ^ = 9.32, P < 0.001). However, species richness did not differ significantly between years in any serai stage, although significant differences between years of different serai stages were detected, but not tested for (one way ANOVA Fg ^

= 3.98, P < 0.001) (Fig. 3.15b).

Table 3.3 Total, adult and nymphal abundance of each major insect group on sites of different successional age over two years (na = number of adults, nn = number of nymphs, NT = total number).

Table 3.3

Serai Stage

Insect GroupRuderal

1985 1986

Early

1985 1986

Early

1985

mid

1986

Late

1985

mid

1986

BLC

1985

BUC

1985

BLC

1986

na 97 256 779 766 694 787 616 1769 634 88 158Heteroptera nn 88 920 846 684 630 696 2176 1816 128 73 94

NT 185 1176 1625 1450 1324 1483 2792 3585 762 161 252-

na 0 11 46 0 10 44 122 625 86 305 139Psyllidae nn - - - - - - - - - - -

NT 0 11 46 0 10 44 122 625 86 305 139

na 1 2 11 7 2 11 6 2 2 0Cercopidae nn - - - - - - - - - - -

NT 1 2 11 7 2 1 1 3 6 2 2 0

na 37 14 85 183 240 i n 361 209 0 0 0Delphacidae nn 47 4 67 230 470 417 626 531 0 0 0

NT 84 18 152 418 710 689 987 740 0 0 0

na 618 517 889 1120 1017 770 644 478 161 81 684Cicadellidae nn 530 125 681 791 1073 1217 803 618 260 166 728

NT 1148 642 1570 1911 2090 1987 1447 1096 421 247 1412

na 434 444 3205 2348 476 216 199 119 79 31 505Curculionoidea nn - - - - - - - - - - -

NT 484 440 3205 2398 476 216 199 119 79 31 505

na 119 147 28 8 24 0 16 20 0 0 0Chrysomelidae nn 109 120 0 0 3 0 3 7 0 0 0

NT 208 267 28 8 27 0 19 27 0 0 0

TotalNT 2130 2556 6637 6187 4639 4430 5569 6198 1350 746 2308

GT = 42,750 CDCO

Fig 3.15 Mean number of insect herbivore species(excluding Aphididae, Coccoidea, Aleyro&oides

(Hemiptera\ Thysanoptera and Lepidoptera) on serai stages of different successional age (a) data summed over two years, (b) for each year (R = ruderal, E = early, EMS = early mid, LMS = late mid, L = late succession). Bars are standard

Clear = 1985, shaded = 1986.errors.

9 4

FIG 3.15

cocoU2CO

8Wcwco

SERAL STAGEb)SPECIES RICHNESS IN 1985 A N D 1986

50 -i----------------------------------------------

I I 1985 1986

95

Annual variation in species richness

Herbivore species richness increased almost linearly in the ruderal stage in 1985 (Fig. 3.16a) (species richness = 1.2 + 7 date, P < 0.05) with 36 species being recorded in September. Species richness in 1986 was similar to 1985 in all months except August, when 55 species were recorded in 1986 compared with only 30 in 1985 (1986, species richness = 1.9 + 8.5 date, P = 0.136). The relationship between species richness and date did not differ significantly between years in the ruderal stage (Kolmogrov-Smirnoff = 0.08, P = 0.98) or in the early serai stage (Kolmogrov-Smirnoff = 0.04, P = 0.98). The number of species in early succession increased from May until August during both years, and then fell by September (Fig. 3.16b). However, the slope of the fitted line was not significantly different from zero in either year (1985, species richness = 14.8 + 7 date, P = 0.055; 1986, species richness = 21.7 + 5.5 date, P = 0.195). Species richness also peaked in August in earlymidsuccession in 1985, (species richness = 15.5 + 7.9 date, P < 0.05) but not until September in 1986 (species richness = 13.7 +9.5 date, P < 0.005), although the relationship between species richness and date was not significantly different between years (Kolmogrov-Smirnoff = 0.04, P = 0.97). Species richness in late midsuccession peaked in August in both years, and again the relationship did not differ between years (Kolmogrov-Smirnoff = 0.03, P = 0.84) (1985, species richness = 30.1 + 2.9 date, P = 0.270; 1986 species richness = 37.8 + 1.8 date, P = 0.627). During both years on late succession species richness increased from May until August and then decreased in September (Kolmogrov-Smirnoff = 0.11, P = 0.805). The greater species richness in 1986 could be due to increased sampling effort (1985, species richness = 8.6 + 1.11 date, P = 0.465; 1986, species richness = 5.3 + 4.3 date, P = 0.117).

Annual variation in species richness of insect groups

Curculionoidea and Heteroptera were the two most species-rich groups in the ruderal and early successional serai stage, with Cercopidae, Psyllidae and Delphacidae being the least

Fig 3.16 Number of insect herbivore species (excluding

Aphididae, Coccoide^, Aleyrodoidea (Hemiptera), Thysanoptera and Lepidoptera) in monthly samples

over two years on serai stages of different successions! age.

SPEC

IES RI

CHNE

SS

9 6

FIG 3.16a)RUDERAL b)EARLY SUCCESSION

c)EARLY MIDSUCCESSION d)LATE MIDSUCCESSION70

60

50

40

50

30

10 0

MAY JUNE AUQ s m MAY JUNE JULY

40

55

50

25

2015

105

0

e)LATE SUCCESSION

AnUL MAY JUNE JULY A1X3 SEPT

1986 + 1985

DATE

97

species-rich (Figs. 3.17a&b). There were no significantdifferences in the species richness of any group between years on either serai stage ( ru d e ra l,^ 2 = 2.092, df = 6, P = 0.911; early, X 2 = 4.927, df = 6, P = 0.553). A similar pattern occurred in the two midsuccessional stages; the Heteroptera was the most species-rich group in 1986 on both sites, whilst the Curculionoidea was the most species-rich in 1 985. Cercopidae and Psyllidae again showed low species richness, but the Delphacidae increased from the level found in the two earlier serai stages. There were no significant differences in species richness between years in either of the midsuccessional stages (EMS, \ 2 = 0.654, df = 6, P = 0.995; LMS,^.2 = 5.019, df = 6, P = 0.542).

Species richness of insect groups feeding on major plant families

A total of 76 species of Heteroptera were recorded, 20 of these were grass-feeders and 15 generalists. Nine Heteroptera species were recorded feeding on trees (Fig. 3.18a). Only one species, Eurydema oloracea specialised on Cruciferae. Ten partially predatory species were recorded (Nabidae and Anthocoridae were considered wholly predatory and consequently not included in this analysis). The majority of the 16 Psyllidae species recorded fed on trees and 4 on minor plant families. All 12 Delphacidae species were grass feeders as were the majority of Cicadellidae. Fourteen of the 17 species of Cicadellidae recorded from trees were members of the subfamily Typhlocybinae, but only one species of this subfamily, Zyginidia scutellaris fed on grass. The only generalist recorded in this group, Empoasca decipiens was also a member of the Typhlocybinae. Two of the three Cercopidae species were grass feeders, and Cercopis vulnerata

was deemed a generalist.

Both of the Coleoptera groups showed wide host ranges. Curculionoidea were recorded feeding on all major plant families except grass and Chrysomelidae from all except the Compositae and birch. Leguminosae had the most species of herbivorous Coleoptera feeding on them and grasses the least.

Fig 3.17 Number of species in each major insect group during two years on serai stages of different successional age (Het = Heteroptera, Psy = Psyilidae, Cere = Cercopidae, Del = Delphacidae, Cic = Cicadellidae, Cure = Curculionoidea, Chry = Chrysomelidae).

SPEC

IES RI

CHNE

SS

98

FIG 3.17

c)EARLY MIDSUCCESSION

t e)LATE SUCCESSION

35 -

30 -

29 -

20 •

d)LATE MIDSUCCESSION

I I 1985 ■ ■ 1986

INSECT GROUP

Fig 3.18 Host plant family of species in each major insect group and summed over all groups (Gen = generalist, Leg = Leguminosae, Co = Compositae, Cr = Cruciferae, P = Polygonaceae, Gr = Gramineae, PP = partial predator, B = birch, mf = minor families). Shaded columns on Cicadellidae indicate Typhlocybinae. Hatched columns on (h) indicate sap-sucking species.

99

FIG 3.18

. c)DELPHACIDAE (DCICADELLIDAE

Leg Co Cr P» Or PP ■ MF

HOST PLANT FAMILYTYPHLOCYBINAE

I ICICADELLIDAE

FIG 3.18

e)CURCULIONOIDEA f)CHRYSOMELIDAE

I I CHEWING INSECTS l - ^vl SAP-SUCKING INSECTSHOST PLANT FAMILY

100

Overall, 70 of the 255 herbivore species fed on grasses and of these only one, Chaetocnema hortensis (Chrysomelidae) was a chewing insect (Fig. 3.18h). Fifty species fed on birch, 15 of these were chewing insects. The plant family with fewest herbivore species was the Cruciferae, which had 7 chewing and one sap-sucking herbivores. Twenty one species were generalists and 23 specialised on plant families not included in any of the major families. Ten species, all Heteroptera, were partially predacious.

3 .3 .b .v i Variation in insect species composition with successional age

Species composition of Heteroptera was most similar between the two midsuccessional stages. There was little difference in the Index of Similarity between the early successional stage and two midsuccessiona! stages and none in that between ruderal and the early and midsuccessional stages (Table 3 .5 ). There was little overlap in species composition of Psyllidae between stages, late mid succession and birch had the most similar fauna, probably due to insects from young trees present on the late midsuccession falling to the ground. The relatively high Index of Similarity of Cercopidae reflects little preference between the serai stages of the few species recorded. Not surprisingly, species composition of Delphacidae on the midsuccessional sites was similar, as was that of the ruderal and early serai stages. More surprising was that the highest Index of Similarity recorded for Cicadellidae occurred between the ruderal and early serai stage. However, comparisons between most stages showed relatively high Indices of Similarity for this group. Indices of Similarity of Curculionoidea were generally lower, the greatest similarity occurred between early and early midsuccession. The same Chrysomelidae species were recorded on the ruderal as on the early successional stage, other comparisons showed little similarity in species composition between stages.

The group mean Index of Similarity showed that insect herbivore species composition in the ruderal stage was most similar to that in the early successional stage, and equally similar to both

Table 3.4

INSECTCROUP

SERAL STAGE

R

85 - 86

E

85 - 86

EMS

85 - 86

LMS

85 - 86

L (LC)

85 - 86

X

85 - 8

Heteroptera 0.68 0.52 0.76 0.65 0.69 0.66

Psyllidae - - 0.4 0.66 0.5 0.52

Cercopidae 1.0 0.66 0.66 0 - 0.58

Curculionoidea 0.66 0.57 0.64 0.66 0.73 0.65

Delphacidae 0.33 1 .0 0.88 0.53 - 0.69

Chyrsomelidae 0.8 0.5 1.0 0.82 - 0.78

Cicadellidae 0.69 0.63 0.90 0.66 0.64 0.70

X 0.69 0.65 0.75 0.56 0.64

Table 3.4 Sorensons Index of Similarity for species in eachmajor insect group between years on serai stages of the same age. (R = ruderal, E = early, EMS = early midsuccession, LMS = late midsuccession, L = late

succession).

102

midsuccessional stages. Species composition in the early serai stage was also equally similar to the two midsuccessional stages, but less similar than to the ruderal stage. The two midsuccessional stages had a species composition most similar to each others than to that on any other serai stage. Notsurprisingly the species composition on birch was most similar to that in late midsuccession. These results indicate that herbivore species composition changes with community age, and overall is most comparable between serai stages of the closest age. However, this may not be true for individual insect groups.

Annual variation in insect herbivore species composition

Cercopidae and Chrysomelidae showed the least variation in species composition between years in the ruderal serai stage (Table 3 .4 ). Species of Delphacidae varied considerably between years in the ruderal serai stage, but not at all on the early successional stage. The three major insect groups, Heteroptera, Cicadellidae and Curculionoidea, varied less between years on the ruderal serai stage than in the early stage. Species of Delphacidae, Cicadellidae and Chrysomelidae varied little between years in the early midsuccession serai stage, but to a greater extent in late midsuccession. Curculionoidea were the most comparable group between years on birch, and Psyllidae the least. The mean Index of Similarity for each year suggested that herbivore species in early midsuccession changed least between years, and those in late midsuccession the most. However, the Index of zero for Cercopidae in this stage lowered this mean. Exclusion of this point gave a mean of 0.66. A similar crude analysis suggested that Chrysomelidae species changed least between years in a serai stage.

3 .3 .b .v ii The Birch Community

Variation in species richness between canopies and years

Forty two herbivore species were recorded on lower canopy 1986, 33 on lower canopy 1985 and 30 on upper canopy 1985 (Table 3 .6 ). The combined species list for 1985 (upper and lower

103

Table 3.5

INSECT CROUP R-E R-EMS R-LMS R-L E-EMS E-LMS E-L EMS-LMS EMS-L LMS-L

Heteroptera Sfcro

O ■tr 0.44 0.263 0.57 0.54 0.27 0.64 0.17 0.13Psyllidau 0 0 0.22 0 0.3 0.5 0 0.4 0 0.8

Cercopidae 0.67 0.67 0.5 0 1.0 0.8 0 0.8 0 0

Delphacidae 0.8 0.57 0.63 - 0.71 0.63 - 0.8 - -

Curculionoidea 0.59 0.57 0.42 0 0.70 0.64 0.07 0.71 0.04 0.08Clccadellidae 0.8 0.66 0.68 0 0.73 0.77 0 0.77 0 0.08Chrysomelidae 1 .0 0.31 0.31 - 0.31 0.31 - 0.43 - -

X 0.61 0.46 0.46 0.053 0.59 0.598 0.068 0.65 0.042 0.218

Table 3.5 Sorensons Index of Similarity for species in each

major insect group between serai stages of different successionai age. Data summed over two years.

Table 3.6 Species richness of each insect group on lower and upper canopy 1985 and lower canopy 1986 in (a) monthly

samples and (b) annual totals.

Table 3.6aDATE

1 2 3 4 5 6year 85 86 85 86 85 86 85 86 85 86 85 86canopy L U L L U L L U L L U L L U L L U L

Heteroptera 3 2 2 3 4 5 8 4 9 8 5 8 9 4 5 3 2 -

Psyllidae 0 1 1 1 1 2 Q 2 3 1 1 3 1 1 2 1 0 -

Ciccadellidae 1 1 2 1 2 3 5 5 8 5 3 10 7 2 10 3 5 -

Curculionoidea 3 2 3 8 6 8 6 4 7 3 3 5 5 1 3 1 1 -

Total 7 6 8 13 13 18 19 15 27 17 12 26 22 8 20 8 8 -

Table 3.6b

year 85 85canopy LC UC LC + UC LC 86

Heteroptera 13 8 15 13

Psyllidae 2 4 4 6

Typhocybinae 8 7 9 10

Cicadellidae 2 2 3 4

Sum 10 9 12 14

Curculionoidea 11 8 11 8

Total 33 30 39 42

104

1 0 5

canopy) showed 39 species, 3 less than recorded in 1986 (50 samples in each year). Species richness of each group except Curculionoidea peaked in midsummer on both canopies, Curculionoidea species richness peaked on date two in upper and lower canopy in both years.

Proportion of adult individuals in each insect group

Heteroptera and Cicadellidae were the dominant groups on the lower canopy in 1985 and 1986 respectively and the Psyllidae on the upper canopy 1985 (Fig. 3.19). The proportion of individuals in insect groups differed significantly between upper and lower canopy 1985 (Kolmogrov-Smirnoff = 0.49, P < 0.001) and between the lower canopy in 1985 and 1986 (Kolmogrov- Smirnoff = 0.57, P < 0.001).

Variation in abundance of Oncopsis between canopies and dates

Abundance of tristis and (X subangulata peaked in July and O, flavicornis in May on both upper and lower canopy in 1985 and 1986.

The dominant species of the genus, expressed as a proportion of total, varied between years and canopies, with Ch flavicornis dominating throughout 1986 and in May 1985, and tristisdominating on the other two dates in 1985. The abundance of each species differed between canopies and years, and no clear patterns emerged from this limited data set (Table 3 .7 ).

3.4 DISCUSSION

Plant species rapidly accumulated onto a ruderal site, and therewas some turnover of species during the first year ofsuccession. During the second year of succession, species- richness and leaf area increased over that of ruderal serai stage, although the number of species and leaf area declined through the second year, the surviving ruderal species dying out and typical midsuccessional species becoming established. Plant species-richness increased through the year in early

Fig 3. 9 Proportion of adults in each major insect group on upper and lower canopy birch 1985 and lower canopy 1986.

% IND

IVID

UALS

/GROU

P

1 0 6

FIG 3.19

10090

8070

60

5040

3020

10

0LOWER CANOPY 1985 UPPER CANOPY 1985 LOWER CANOPY 1986

CANOPY

HETEROPTERA PSYLLLDAE

CICADELLLDAE CURCULIONOIDEA

1 0 7

Table 3.7

CANOPY

LOWER UPPER

SPECIES 0. tristis 0. flavicornis 0. subanquiata 0. tristis CL flavicornis 0. subanaulata

DATE no P no P no P n o P no P no P

10/5/85 0 C 11 1.0 0 0 0 0 19 0.9 2 0. 1

4/7/85 16 0.55 8 0.28 5 0.17 6 0.46 1 0.46 6 0.08

24/7/85 6 0.75 2 0.25 0 0 1 1 .0 0 0 0 0

10/6/86 6 0.032 128 0.69 51 0.28

7/7/86 37 0.26 87 0.61 18 0.13

11/8/86 3 0.25 8 0.75 0 0

Abundance (no) and proportion (P) of total abundance on Qncopsis (Hemiptera: Cicadellidae) in upper and lower canopy 1985 and lower canopy 1986.

1 0 8

midsuccession. During this serai stage Leguminosae became less

important in terms of leaf area, grasses and Compositae becoming dominant. The early midsuccessional serai stage was the most species-rich, as well as producing most leaf area. Little change occurred from early to late midsuccession, both species richness and leaf area decreased slightly, but the community changed little, being dominated by grasses, though several new species did occur on this site eg Betula, Quercus, Cytisus, Rubus and Chamaerverion. Despite differences between serai stages, significant differences in community attributes between years in stages of the same age were rare. Species richness, the proportion of the community's leaf area provided by each family and dominant species/family were all comparable between years, although leaf area did differ between years on all stages except the ruderal stage.

The insect community also changed with succession. Total species richness increased with the age of the serai stage up to late midsuccession, whereas insect abundance was greatest on early succession and least on late succession. The different insect groups showed different patterns of numerical abundance with succession, reflecting primarily the abundance of their respective host plants. Species richness increased through the season on all serai stages, however the pattern of insect abundance varied with serai stage, it increased with date on the ruderal stage, decreased on birch and peaked in midsummer during midsuccession. There was remarkable similarity in species richness and abundance of herbivorous insects between years on sites of the same age. This suggests the existence of some structuring force(s) in these communities.

The results of this study agree well with those of other studies on this system (see section 3.1 for references). Southwood, Brown & Reader (1979) report 38 plant species at the end of the first year of succession and the "extinction of primary colonisers" within 18 months, these are similar to results gained here. They report the oC-diversity of plants and insectspeaking in early succession. No such analysis was undertaken in this study. Plant species richness was highest in early

109

midsuccession and slightly less in early succession, a consideration of the total leaf area provided by the dominant species (P^) suggests that such a measure of diversity would be greatest in early midsuccession. Although the species richness of insect herbivores was slightly greater in late midsuccession than early and early midsuccession, the abundance of insects in early succession suggests a calculated diversity index would be greatest for this serai stage. It is interesting to note that a consideration of herbivore abundance between serai stages based on equal sample sizes alone, would yield no results either for the total insect community or for any individual group, in agreement with the prediction of Lawton & McNeill (1979).

110

CHAPTER FOUR

ABSOLUTE ABUNDANCE OVER A SUCCESS1CNAL GRADIENT

4.1 INTRODUCTION

This chapter presents data which aim to test Lawton S McNeill's (1979) hypothesis that the absolute abundance of insect species on early successional plants is greater than that of species on late successional plants. Godfray (1985) tested this hypothesis for leaf-mining insects and found it to be true. However, only one year's data were presented and leaf miners may well differ from external-feeding insects in their relationship with the host plant.

The hypothesis was examined in several different ways. Initially, variation in the pattern of absolute abundance with the

successional age of the habitat was examined; the null hypothesis being that absolute abundance did not vary between different successional stages. These data were then split by date and the hypothesis tested for individual dates. Then data for non-woody plant-feeding species were compared with those for woody plant­feeding species. Here, the null hypothesis was that the absolute abundance of species feeding on non-woody and woody plants was not different. In reality this provided a comparison of the absolute abundance of species feeding on plants defended by qualitative defences with that of species feeding on plants defended by quantitative defences. Again the null hypothesis was tested for the whole sampling period and for separate dates.

For major plant families, the absolute abundance of associated species was compared over the whole successional gradient and within each serai stage to test the null hypotheses that absolute abundance of species feeding on these families was consistent within serai stages, and that absolute abundance of species feeding on a particular plant family did not vary between different serai stages. This analysis aimed to provide some insight into the effects of different qualitative defences on the absolute abundance of the associated herbivores, and on the

I l l

variation in the abundance of herbivores feeding on any one

plant family in different successional stages. In the lattercase, it is assumed that species feeding on a plant family would be subjected to similar chemical defences although other attributes of the habitat would change according to successional age. Taking a single insect family, the Cicadellidae, a similar analysis compared the absolute abundance of species regarded as specialists on Holcus spp and Agrostis spp (Gramineae) in habitats of different successional age. Here the null hypothesis being tested was that there was no difference in the abundanceof species feeding on the same host plant when it occurred onsites of different successional age. Holcus and Agrostis spp were chosen as they were common on the four younger seraistages. A difference in feeding habits of one subfamily of the Cicadellidae, the Typhlocybinae, allowed a unique analysis to be undertaken. The majority of Cicadellidae species feed on phloem, whereas Typhlocybinae feed on mesophyll cells (Claridge & Wilson 1981). Thus, if the concentration and/or nature of defensive compounds varied between phloem and mesophyll, the patterns of abundance of species feeding on these tissues may differ. In this case, the null hypothesis was that the absolute abundance of species of Typhlocybinae varied in a similar manner to that of phloem-feeding Cicadellidae.

4.2 METHODS

All field methodology and rationale are discussed in Chapter 2. The null hypotheses outlined in the introduction were tested for dominant herbivore groups: Cicadellidae, Delphacidae,Cercopidae, Psyllidae (Hemiptera: Homoptera); Heteroptera(Hemiptera) and Chrysomelidae, Curculionoidea (Coleoptera). Initially, each group was tested to determine whether it followed a gamma distribution, as described in section 2.3. Since no a posteriori significance tests were employed, overall probability values are presented and patterns of absolute abundance discussed.

112

4.3 RESULTS

4 .3 .i Distribution of absolute abundance

In the Cicadellidae, Delphacidae and Curculionoidea the fitted line of standard deviation passed through the origin and its slope was significantly different from zero, indicating that the data were gamma distributed. However, this was not the case in the Heteroptera, the data for which were analysed by standard non- parametric tests. The same tests were applied to the minor insect groups (Chrysomelidae, Psyllidae and Cercopidae) where the sample sizes were small. The regression analyses are given

in Appendix 3.

4 .3 .ii Absolute abundance in relation to serai stage

Cicadellidae

There was a significant difference in the absolute abundance ofCicadellidae species by host plant family and host plant speciesbetween serai stages (abhf, = 104.03, P < 0.001; abhs,F,.. = 139.96, P < 0.001). Generally absolute abundance byl Jhost plant family and species decreased with increasing successional age (Fig. 4 .1 ). There were significant effects of date and date, sera I stage interaction for absolute abundance by host plant family and species. There were some clear trends in monthly abundance by host plant family and species, with a tendency for the highest abundance to be associated with the ruderal stage (Fig. 4.2) and generally declining with increasing successional age. Although there was no overall seasonal change, abundance by host plant family in July and August was greatest in early succession, and in June and July the value for late succession was marginally higher than for late midsuccession. No value for absolute abundance by host plant species could be calculated for species on the ruderal serai stage during May. By June, however, large numbers of Macrosteles gave values of absolute abundance approaching 1000/m2 of leafarea.

Fig 4.1 Mean absolute abundance of Cicadellidae by (a) host plant family, (b) host plant species in different serai stages (R = ruderal, E = early succession, EMS = early midsuccession, LMS = late midsuccession, L = late succession). Bars are standard errors.

113

FIG 4.1

8

1

a)ABSOLUTE ABUNDANCE BY HOST PLANT FAMILY

SERAL STAGE

b)ABSOLUTE ABUNDANCE BY HOST PLANT SPECIES

i i l lR E EMS LMS LSERAL STAGE

Fig 4.2 Mean absolute abundance of Cicadellidae by (a) host plant family, (b) host plant species from May to September in different serai stages. Bars are standard errors.

114

FIG 4.2a)ABSOLUTE ABUNDANCE BY HOST PLANT FAMILY

M AY JUNE JULY AUG SEPTDATE

| [ RUDERAL

F T ] EARLY SUCCESSION

B | EARLY MIDSUCCESSION

□ LATE MIDSUCCESSION

LATE SUCCESSION

115

Delphacidae

In this group there was a significant difference between serai stages in absolute abundance by host plant species (F ^ =32.82, P < 0.001), but not in absolute abundance by host plant family (F ^ = 1.59, P > 0 .05 ), with the greatest abundanceoccurring in early midsuccession (Fig. 4 .3 ). This was particularly clear when abundance by host plant species was considered and was due mainly to high numbers of Stenocranus minutus in September 1985 which feeds on Dactyl is glomerata. There was a significant effect of date in the fitted model for absolute abundance by host plant family and species, although there was only a significant serai stage.date interaction for absolute abundance by host plant family. Monthly data forabsolute abundance by host plant family and host plant species showed few clear trends. As might be expected from the above, the highest values were generally associated with midsuccession, being particularly apparent in September (Fig. 4 .4 ).

Curculionoidea

This group also showed significant differences in absolute abundance by host plant family and species between serai stages

(abhf, F(4 j = 164.59, P < 0.00 ; abhs F(4 287) = 133*04'P < 0.001). In both cases, the lowest abundance was recordedin late succession, with abundance by host plant family and species being greatest in ruderal and midsuccessionrespectively (Fig. 4 .5 ). There was a significant effect of date and date.serai stage in the fitted model of absolute abundance by host plant family. It was not possible to fit the effect of date for absolute abundance by host plant species as the fitted mean was out of range of the model. A Kruskall-Wallis test showed that there was a significant difference in the distribution of absolute abundance by host plant species between dates

(Kruskall-VVallis = 15.227, P < 0.01, n = 294) with abundance being generally higher later in the year. The pattern ofabsolute abundance by host plant family changed through the year, being greatest in the ruderal stage early in the year, and in midsuccession in September. In contrast, absolute abundance

Fig 4.3 Mean absolute abundance of Delphaciaae by (a) host plant family, (b) host plant species in different serai stages (R = ruderal, E = early succession, EMS = early midsuccession, LMS = late midsuccession). Bars are standard errors.

ABSO

LUTE

ABU

NDAN

CE

ABSO

LUTE

ABUN

DANC

E

1 1 6

FIG 4.3

SERAL STAGE

Fig 4.4 Mean absolute abundance of Delphacidae by (b) host plant family (a) host plant species from May to September in different serai stages. Bars are standard errors.

ABSO

LUTE

ABUN

DANC

E AB

SOLU

TE AB

UNDA

NCE

117

FIG 4.4

DATE

□ RUDERAL

EARLY SUCCESSION

^ LATE SUCCESSION

H P EARLY MIDSUCCESSION S LATE MIDSUCCESSION

Fig 4.5 Mean absolute abundance of Curculionoidea by (a) host plant family, (b) host plant species in different serai stages. Bars are standard errors.

1 1 8

FIG 4.5

e

800

8

5

Ico5

a)ABSOLUTE ABUNDANCE BY HOST PLANT FAMILY

SERAL STAGEb)ABSOLUTE ABUNDANCE BY HOST PLANT SPECIES

SERAL STAGE

Fig 4.6 M ean a b s o lu t e a b u n d a n c e o f C u r c u i io n o id e a b y (a)

h o s t p la n t f a m i l y , (b ) h o s t p la n t s p e c ie s fro m M a y

to S e p t e m b e r in d i f f e r e n t s e r a i s t a g e s . B a r s a r e

s t a n d a r d e r r o r s .

119

FIG 4.6

8

5

800 a)ABSOLUTE ABUNDANCE BY HOST PLANT FAMILY700 -

600 -

500 -

400 -

300 -

OCO 200 H

100 -

0s

MAY JUNE JULYDATE

AUG SEPT

□ RUDERAL

fvTl EARLY SUCCESSION

LATE SUCCESSION

EARLY MIDSUCCESSIONLATE MIDSUCCESSION

120

by host plant species was greatest in midsuccession throughout the year (Fig. 4 .6 ).

Heteroptera

Absolute abundance by host plant family and species was distributed in a significantly different manner between serai stages, showing basically similar patterns for both measures of abundance, with the highest levels being seen in the ruderal and early midsuccessional stages (Fig. 4 .7 ). The pattern of abundance between serai stages was different on each month (Fig4 .8 ) . No discernible patterns appear from these data.

Minor insect groups - Psyllidae, Cercopidae, Chrysomelidae

There were significant differences in the distribution of absolute abundance by host plant family of Chrysomelidae and Psyllidae between serai stages, but not of Cercopidae. Absolute abundance by host plant species of Psyllidae and 'Chrysomelidae

was distributed differently between serai stages, while there was no difference in the distribution of Cercopidae Absoluteabundance of Chrysomelidae was greatest in early succession and declined progressively with increasing successional age (Fig4 .9 ) . No Chrysomelidae were recorded on birch. The patterns of absolute abundance by host plant family and species of Psyllidae differed markedly: abundance by host plant family was greatest in late midsuccession, whereas abundance by host plant species decreased with increasing successional age (Fig. 4 .10). The high abundance by host plant family in late midsuccession was due to the broom-feeding species Arytainilla spartiophila. This species was recorded in D-vac samples and therefore had to be considered as a legume feeder, although it is probably species specific. Exclusion of broom-feeding species from the analysis did not affect the results (Kruskall-Wallis = 18.436, n = 47, P < 0.01). Absolute abundance by host plant family of Cercopidae was greatest in late midsuccession, and abundance by host plant species on the ruderal stage. One individual of Aphrophora alni was recorded from birch in each year (Fig.4.11).

Fig 4.7 Mean absolute abundance of Heteroptera by (a) host plant family, (b) host plant species in different serai stages (abhf, Kruskall- Wallis = 45.602, n = 342, P < 0.0001; abhs, Kruskall-VVallis = 79.522, n = 167, P < 0.001) (R = ruderal, E = early succession, EMS = early midsuccession, LMS = late midsuccession, L = late succession).

121

FIG 4.7

8

3

3

a)ABSOLUTE ABUNDANCE BY HOST PLANT FAMILY

SERAL STAGE

8

oco

1200 b)ABSOLUTE ABUNDANCE BY HOST PLANT SP1100 -

1000 -

900 -

800 -

700 -

600 -

500 -

400 -

300 -

200 -

100 -

0 EMS LMSSERAL STAGE

iCEES

Fig 4.8 Mean absolute abundance of Heteroptera by (a) host plant family, (b) host plant species from May to September in different serai stages (abhf, May, Kruskall-Wallis = 3.621, n = 25, P = 0.46; June, Kruskall-Wallis = 6.918, n = 37, P = 0.14; July, Kruskall-Wallis = 16.304, n = 74, P < 0.01; August, Kruskall-Wallis = 30.703, n = 97, P < 0.0001; September, Kruskall-Wallis = 1.9218, n = 90, P = 0.7501 ; abhs, May, Kruskall-Wallis = 2.2319, n = 12, P = 0.5257; June, Kruskall-Wallis = 13.047, n = 22, P < 0.01; July, Kruskall- Wallis = 23.651 , n = 39, P < 0.0001 ; August, Kruskall- Wallis = 36.439, n = 52, P < 0.001); September, Kruskall-Waliis = 11.314, n = 41 , P < 0.05).

1 2 2

FIG 4.8

a)ABSOLUTE ABUNDANCE BY HOST PLANT FAMILY

EMSDATE

3500 b)ABSOLUTE ABUNDANCE BY HOST PLANT SPECIES

B 3000 -

2500 -

2000 -

1500 -OCO$ 1000 -

500 -

EMSDATE

□ RUDERAL

[W ] EARLY SUCCESSION

5^1 l a t e s u c c e s s io n

LMS L

EARLY MIDSUCCESSION LATE MIDSUCCESSION

Fig 4.9 Mean absolute abundance of Chrysomelidae by (a) host plant family, (b) host plant species in different serai stages (R = ruderal, E = early succession, EMS = early midsuccession, LMS = late midsuccession). (abhf, Kruskall-Wallis = 9.6894, n = 58, P < 0.05; abhs, Kruskall-Wallis = 12.46, n = 23, P < 0 . 0 0 1 ).

ABSO

LUTE

ABUN

DANC

E AB

SOLU

TE AB

UNDA

NCE

1 2 3

FIG 4.9400 a)ABSOLUTE ABU N D A N C E B Y HOST PLANT FAM ILY

350

300

250

200

150

100 50

0 R E EMS LMS L

SERAL STAGE

3500 b)ABSOLUTE ABU N D A N C E B Y HOST PLANT SPECIES

3000 -

2500 -

2000 -

1500 -

1000 -

500 -

EMS LMS

SERAL STAGE

Fig 4.10 Mean absolute abundance of Psyllidae by (a) host plant family, (b) host plant species in different serai stages (R = ruderal, E = early succession, EMS = early midsuccession, LMS = late midsuccession, L = late succession), (abhf, Kruskall-Wallis = 24.9296, n = 38, P < 0.0001; abhs, Kruskall-Wallis = 25.794, n = 48, P < 0 . 0001 ) .

1 2 4

FIG 4.10a)ABSOLUTE ABUNDANCE BY HOST PLANT FAMILY

R EMS LMSSERAL STAGE

Fig 4.11 Mean absolute abundance of Cercopiaae by (a) host plant family, (b) host plant species in different serai stages (R = ruderal, E = early succession, EMS = early midsuccession, LMS = late midsuccession, L = late succession). (abhf, Kruskall-Wallis = 3.6276, n = 2 0 , P = 0.4587; abhs, Kruskall-Wallis = 11 .2561 , n = 2 0 , P = 0.0238).

ABSO

LUTE

ABUN

DANC

E AB

SOLU

TE AB

UNDA

NCE

FIG 4.11a)ABSOLUTE ABUNDANCE BY HOST PLANT FAMILY

SERAL STAGE

900 b)ABSOLUTE ABUNDANCE BY HOST PLANT SPECIES800 -

700 -

600 -

500 -

400 -

300 -

200 -

100 -

0 --EMS

SERAL STAGELMS

1 2 6

4.3 .iii Absolute abundance of woody and non-woody plants

Absolute abundance by host plant family and species of Cicadellidae, Psyllidae, Heteroptera and Curculionoidea was significantly greater on non-woody plants than on woody plants over the whole season, and generally on each individual date (Figs. 4.12 - 4.15 & Tables 4.1 & 4 .2 ). However, absoluteabundance by host plant family of Heteroptera on woody plants in May was greater than that on non-woody plants. This anomaly was due to the abundance of Kleidocerys resedae (Lygaeidae) on birch in that month.

4 .3 .iv Absolute abundance on major plant families

There were significant differences in the absolute abundance of insects associated with major plant families in all groups tested (Curculionotied'. abhf, 7 9 ) = 198.4, P < 0.001, abhs,F^s 2 7 3 ) = 157.74, P < 0.001; Heteroptera: abhf, Kruskall-Wallis = 74.02, n = 321, P < 0.001, abhs, Kruskall-Wallis = 73.767,n = 179, P < 0 . 0 0 1 ; Psyllidae: abhf, Kruskall-Wallis = 31.922,n = 57, P < 0 . 0 0 1 , abhs, Kruskall-Wallis = 25.029, n = 48,P < 0.001). Absolute abundance of Curculionoidea by host plantfamily was greatest on Cruciferae, while by host species it was greatest on the Leguminosae with Compositae and Cruciferae also having high abundances of insects (Fig. 4.1 A). Abundance of Heteroptera by host plant family was also greatest on Cruciferae, although that by host species was greatest on Compositae (Fig. 4 .17). The high value for host species on Compositae reflects the abundance of Tingis ampliata (Tingidae) which feeds on Cirsium arvense. A very different pattern of abundance occurred in the Psyllidae, where absolute abundance by host plant family was greatest on Leguminosae and that by host plant species on Polygonaceae. The latter analysis excluded broom-feeding species, whereas analysis of abundance by host plant family included as legume feeders (Fig. 4 .10). Exclusion of broom-feeding species did not alter the results of the analysis by host plant family (Kruskall-Wallis = 16.619, n = 47, P < 0.001). In all cases absolute abundance on birch was lower than on any major plant family. There was a significant family.serai

Fig 4.12 Mean absolute abundance of Cicadellidae, Heteroptera and Psyllidae by host plant family and host plant species feeding on woody and non-woody plants. Bars on (a) and (b) are standard errors. Heteroptera, abhf, Kruskall- Wallis = 26.678, n = 308, P < 0.0001 ; abhs, Kruskall-Wailis = 71 .558, n = 166, P < 0 .0 0 0 1 . Psyllidae, abhf, Kruskall-Wailis = 31.096, n = 57, P < 0.001; abhs, Kruskall-Wallis = 24.783, n = 48, P < 0 . 0 0 0 1 .

ABSO

LUTE

ABUN

DANC

E

1 2 7

FIG 4.12 CICADELLIDAEa) ABSOLUTE ABUNDANCE b) ABSOLUTE ABUNDANCEBY HOST PLANT FAMILY BY HOST PLANT SPECIES

HETEROPTERAc) ABSOLUTE ABUNDANCE

BY HOST PLANT FAMILYso

40 -

30 -

20 -

10 -

NONWOODY WOODY

d) ABSOLUTE ABUNDANCE BY HOST PLANT SPECIES500 ■ [ ■ 1 ■

400 -

300 «

200 -

100 •0 * I '■ T

NONWOODY WOODY

PSYLLIDAEf) ABSOLUTE ABUNDANCE BY HOST PLANT SPECIES

NONWOODY

CD all srecms .BROOM FEEDERS PLANT TYPE

Fig 4.13 Mean absolute abundance of Cicadellidae by (a) host plant family, (b) host plant species feeding on woody and non-woody plants from May to September. Bars are standard errors. (abhf, F ^ 9 4 ) = 19.33, P < 0.001; abhs, F ^ 1?6) = 12.24, P <'0.001).

1 2 8

FIG 4.13

DATE

I 1 NONWOOD Y PLANTS C H J WOODY PLANTS

Fig 4.14 Mean absolute abundance of Heteroptera by (a)host plant family, (b) host plant species feeding on woody and non-woody plants from May to September (hatched bars = woody plants, clear bars = non-woody plants) (abhf, May, Kruskall- Wallis = 0.4875, n = 24, P = 0.4851 ; June,Kruskall-Wallis = 2.4217, n = 35, P = 0.1197; July, Kruskall-Wallis = 7.443, n = 74, P < 0 . 0 1 ; August, Kruskall-Wallis = 24.839, n = 1 0 0 , P < 0.001; September, Kruskall-Wallis = 0.2026, n = 8 8 , P = 0.6592; abhs, May, Kruskall-Wallis = 0.7200, n = 14, P = 0.3961 ; June, Kruskall-Wallis = 7.031, n = 25, P < 0 . 0 1 ; July, Kruskall- Wallis = 14.986, n = 42, P < 0.0001 ; August, Kruskall- Wallis = 28.309, r, = 55, P < 0.001); September, Kruskall-Wallis = 6.079, n = 43, P < 0.05).

1 2 9

a)ABSOLUTE ABUNDANCE BY HOST PLANT FAMILY

FIG 4.14

b)ABSOLUTE ABUNDANCE BY HOST PLANT SPECIES

DATE

I I NONWOODY PLANTS F T l WOODY PLANTS

Fig 4.15 Mean absolute abundance of Psyllidae by (a) host plant family and (b) host plant species feeding on woody and non-woody plants from May to September. Insufficient data to allow statistical comparisons.

1 3 0

a)ABSOLUTE ABUNDANCE BY HOST PLANT FAMILY

FIG 4.15

b)ABSOLUTE ABUNDANCE BY HOST PLANT SPECIES

I INONWOODY PLANTS E D WOODY PLANTS

Absolute Abundance Plant Type Lowest SE Mean Highest SE

host plant family non-woody 96.99 105.22 114.97

host plant species non-woody 1933.7 2228.6 2629.8

host plant family woody 0.758 0.933 1.214

Table 4.1 Mean absolute abundance and standard errors of Curculionoldea by host plant family and species feeding on

woody and non-woody plants, abhf, ^9 4 ) = 150.26, P <

0.001); abhs, F (1 282) = 430.97, P < 0.001.

Table 4.2 Mean absolute abundance and standard errors of Curcuiionoidea by host plant family and species feeding on woody and non-woody plants on each date. Data pooled over two years, (abhf, date F(4 , 3 9 4 ) = 't'K0It- P < 0 -0 0 1 - data.plant F{a = 1 .5006, P > 0.05; abhs, date 282) = 53.23, P < 0.001, date.plant = ^*^06, P > 0.05.

Table U.2

(a) Absolute abundance by host plant family

Date Lowest SENon-woody

MeanPlants

Highest SE Lowest SEWoody Plants

Mean Highest SE

May 1 0 1 . 0 121.9 153.7 0.079 0.136 0.449

June 39.02 45.97 55.96 0.057 0.093 0.244

July 38.64 45.72 55.97 0.047 0.082 0.306

August 162.6 188.2 223.3 0.G35 0.060 0.226

September 165.3 193.3 232.5 0.040 0.089 0.042

(b) Absolute abundance by host plant species

Date Lowest SE

Non-woody Plants

Mean Highest SE Lowest SEWoody Plants

Mean Highest SL

\lay 2466.99 3430.53 5630.63 0.079 0.136 0.449

June 363.57 492.61 763.65 0.057 0.093 0.244

July 2744.55 3732.74 5832.90 0.047 0.082 0.306

August 4044.3 5243.8 7454.89 0.035 0.060 0.226

September 1557.87 2076.4 3112.35 0.040 0.089 0.042

132

Fig 4.16 Mean absolute abundance of Curculionoidea by (a) host plant family, (b) host plant species on major plant families [data pooled over all dates and all serai stages) (L = Leguminosae, Co = Compositae, Cr = Cruciferae, Po = Poiygonaceae, B = birch). Bars are standard errors.

ABSO

LUTE

ABUN

DANC

E AB

SOLU

TE AB

UNDA

NCE

1 3 3

a)ABSOLUTE ABUNDANCE BY HOST PLANT FAMILYFIG 4.16

PLANT FAMILY

b)ABSOLUTE ABUNDANCE BY HOST PLANT SPECIES5200 t -----------------------------------------------------------------------------------------------------3000 - 2800 - 2600 - 2400 - 2200 -

2000 -

1800 - 1600 - 1400 - 1200 -

1000 -

800 - 600 - 400 - 200 -

0 -- T ”Cr

T"Po Birch

PLANT FAMILY

Fig 4.17 Mean absolute abundance of Heteroptera by (a) host plant family, (b) host plant species on major plant families (data pooled over all dates and all seraistages) (L = Leguminosae, Co = Compositae, Cr =Cruciferae, Po = Polygonaceae, B = birch, Cr = Gramineae, MF = minor families, G = generalist (species associated with more than one plant fam ily)).

ABSO

LUTE

ABU

NDAN

CE

ABSO

LUTE

ABU

NDAN

CE

1 3 4

aYABSOLUTE A BU N D A N C E B Y HOST PLANT FAM ILY

FIG 4.17

PLANT FAM ILYb)ABSO LUTE A B U N D A N C E B Y H OST PLANT SPECIES

G L Co Cr Po Gr MF BPLANT FAMILY

Fig 4.18 Mean absolute abundance of Psyllidae by (a) host plant family, (b) host plant species on major plant families. Data pooled over all dates andserai stages. (L = Leguminosae, Co =Compositae, Po = Polygonaceae, MF = minor families, B = birch).

ABSO

LUTE

ABUN

DNAC

E AB

SOLU

TE A

BUND

NACE

1 3 5

FIG 4.18

PLANT FAMILY

1000b)ABSO LUTE A BU N D A N C E B Y HOST PLANT SPECIES

900 -

800 -

700 -

600 -

500 -

400 -

300 -

200 -

100 - 0 T

Co TPo MFPLANT FAMILY

Fig 4.19 Mean absolute abundance of Heteroptera by (a) host plant family, (b) host plant species on herbs, grass and birch (data pooled over all dates and serai sta g e s).

ABSO

LUTE

ABUN

DANC

E AB

SOLU

TE AB

UNDA

NCE

136

FIG 4.19

50 a)ABSOLUTE ABUNDANCE BY HOST PLANT FAMILY

40 -

30 -

20 -

10 -

HERBS GRASS BIRCHPLANT TYPE

b) ABSOLUTE ABUNDANCE BY HOST PLANT SPECIES

PLANT TYPE

1 3 7

stage interaction for Curculionoidea for abundance by host plant family and species (abhf, = 14.49, P < 0.001, abhsF(9 273) = 42,65' P < 0 . 0 0 1 ). In the younger serai stages absolute abundance by host plant family of Cruciferae-feeding species was the greatest, with that of Compositae-feeding species being the least (Table 4 .3 ). In addition, there were different patterns of absolute abundance in the two midsuccessional serai stages, with the Polygonaceae-feeding species being dominant in early midsuccession and the Leguminosae-feeding species in late midsuccession. Apart from the ruderal stage where Cruciferae- feeding species were again dominant, absolute abundance by host plant species showed different patterns; with that of Leguminosae-feeding species being the greatest throughout the other serai stages, and Polygonaceae-feeding species being the least. Absolute abundance by host plant family of Heteroptera- feeding on major plant families differed significantly in distribution in all serai stages except for early succession where insects associated with • Leguminosae were dominant (Table 4 .4 ). In contrast the distribution of absolute abundance by host plant species between plant families was only significantly different on the ruderal serai stage. Cruciferae-feeding species were only found on the ruderal stage, whereas Leguminosae- feeding species reached their highest abundance in early succession. In both midsuccessional stages, however, Polygonaceae-feeding species showed the greatest absolute abundance and were particularly marked in EMS. Analysis by host plant species revealed different patterns, with Leguminosae-feeding species dominant in late midsuccession, and Compositae-feeding species in early midsuccession. OnlyLeguminosae-feeding species showed significant differences in the distribution of absolute abundance by host plant family between serai stages, and only grass-feeding species by host plant species.

The Heteroptera occurred at all successional stages and demonstrated that species feeding on herbaceous dicotyledons had greater absolute abundances than those feeding on grass and these in turn had greater absolute abundances than birch-feeding species (Fig. 4 .IS ) (abhf, Kruskall-VVallis = 30.0142, P < 0.0001 , abhs, Kruskall-Wallis = 61.33, P < 0 .0 0 0 1 ) .

138Table 9.3a

p la n t fam ily

SERAI. STAGE Lcguminosae Compost tae Crucitcrae Polygonaceae B irch

mean '10.5 13.2 3 31.9 37.1

KuderalSB 32.6 53.5 5.26 27.3 298.2 998.8 25.15 70.62

mean 7'1.8 u.7 915.2 198.8

Earlysuccession

SE 6 <1.8 88.6 1.9 0.8 298.9 126.9 135.2 375.9

mean 86.5 2.11 11 .92 192.8

Ea rly mid midsuccession

SE 7«.2 103.7 1.2 8.9 9.76 25.3 85.95 939.8

mean 137.9 16.72 - 22.1

Late mid midsuccession

SE 117.0 167.8 8.96 125.5 13.67 56.9

mean _ - - 0.93

Latesuccession

SE 0.76 1.197

Table 9.3b

p la n t fam ilySERAL STAGE Leguminosae Compositae Cruciferae Polygonaceae Minor families

Ruderalmean 93.9 569.9 6218.9 38.31 76.7SE 27.9 96.9 307.7 3831.9 3978.6 19232.9 2133 187.9 96.7 215.9

Earlysuccession

mean 9616.8 953.3 399 52.99 392.8

SE 3693.7 6298.8 960.8 1800.1 196.3 9950 27.61 657.9 183.0 269S.9

Ea rly mid midsuccession

mean 2932.5 180.5 155.8 19.16 29.5

SE 1859.1 3517.«» ISO.9 299.9 99.0 307.9 9.355 33.21 9.8 97.9

Late mid midsucccssion

mean

SE

6006

9319.1 9881.9

6.095

1.87 13.52

17.27

5.50 39.5

Table 4 . 3 Mean absolute abundance and standard errors of Curculionoidea by (a) host plant family, (b) host plant species on major plant families in different serai stages. See text for significance levels.

1 3 9

Serai Sta<jo Lcguminosae Compositae jC ruc ile rac Polyponaceae Craminae Generalist liirc h Significance

Ku ile ra l 0.95; 13.38 612.9 30.35 2.972 5.936 -

KW = 10.79 n = IS P < 0.05

Earlysuccession

130.80 - | -!8.53 3.860 11.250 -

KW = 1.3969 n = 23 P = 0.51

Ea rly miii j 45.46 succession

1 ij - j 137.70 0.880 59.10 -

KW = 29.791 9 n = 82 P < 0.0001

Late mid succession

19.20 3.51 - 22.76 7.30 5.12 -

KW = 11 .0209 n = 71 P < O.OS

Latesuccession

- - i2.08 9.796 '

SiyitiiicauceKW = 19.086 n = 29 P < 0.01

KW =1. 33

P = 0.298-

KW = 5.081 n = 15 P = 0.160

KW = 9.88 n = 90 P = 0.299

KW = 6.97 it = 123 P = 0.166

-

Table 9.9a

Scr.il Stage Legummosaei Compost tae C ruciferae Polygonaceae Craminae Generalist U irc lt Significance

jKudcral j 7,079

1

- 182.9 209.2 0.6099 299.5 -

KW = 29.01 n = 10 P < 0.00

1Early j 63.39 succession ! !

!

- 97.19 160.6 . -

KW = 3.19 n = 59 P = 0.53

Ea rly mid j 197.8 succession

9708.0 j1 - 209.6 259.7 -

KW = 1.703 n s 38 P = 0.636

Late mid J 57.98 succession j

i

95.29 - - 98.89 96.69 -

KW = 3.908 n = 92 P S 0.99

Latesuccession

“ * " - - 2.00 9.796 -

SignificanceKW = 9.69 n = ie P = 0.20

KW = 2.37 n = 17 P = 0.12

- -KW = 12.7 n = 98 P < 0.01

KW = 16.22 n = 37

P < 0.05

- -

Table 9.9b

Table 4.4 Mean absolute abundance of Heteroptera by (a) host plant family, (b) host plant species on major plant families in different serai stages. Differences between plant families and serai stages tested by Kruskall-YVallis one way ANOVA.

Fig 4.20 Mean absolute abundance of Cicadellidae by host plant species feeding on (a) Agrostis and (b) Holcus (Gramineae) in different serai stages (R = ruderal, E = early succession, EMS = early midsuccession, LMS = late midsuccession). Bars are standard errors.

140

FIG 4.20alAGROSTIS spp

1000wy 900

< 800

§ 700

9 600

500R 400H-Jo 300

200

100

0 E EMSSERAL STAGE

LMS

blHOLCUS spp

SERAL STAGE

1 4 1

4 .3 .v Absolute abundance and species composition of Cicadellidae feeding on Holcus and Agrostis spp

There was a significant difference in the absolute abundance of species feeding on both Agrostis and Holcus between serai stages (A grostis: 2 9 ) = 34.55, P < 0 . 0 0 1 ; Holcus: 5 7 ) = 10.14,P < 0.001). In both grass species the greatest insect absolute abundance occurred on the ruderal stage, with the lowest value of Agrostis-feeding species occurring in early midsuccession and in early succession for Holcus-feeding species (Fig. 4 .20). Three of the four species of Cicadellidae which fed specifically on Agrostis spp and three of the six Hoicus spp specialists were recorded on the four younger serai stages (Table 4 .4 ). The abundance of these species varied between serai stages. There was no discernible pattern in the abundance of Agrostis feeding species, although the Holcus-feeding species tended to increase in abundance with increasing successional age (Table 4 .5 ).

4 .3 .v i Comparison of absolute abundance of phloem and mesophyll-feeding Cicadellidae

Different patterns of absolute abundance emerged when phloem and mesophyll-feeding Cicadellidae were considered separately (Fig. 4 .21). Absolute abundance by host plant family of phloem-feeding Cicadellidae was greatest on the ruderal stage and least in late midsuccession, while that of Typhlocybinae combined to decrease with increasing successional age. There were significant differences in absolute abundance by host plant family and species for Typhlocybinae and phloem-feeding Cicadellidae (phloem-feeding Cicadellidae: abhf, F,57.57, P < 0.001; abhs, FffI 11C, = 35.34,Typhlocybinae: abhf, F(162.9, P < 0.001). (4,64)

(4,116)= 582.8, P < 0.001; abhs F(4,315)P < 0.001;

(4,74)

Absolute abundance by host plant species of Typhlocybinae and phloem-feeding Cicadellidae decreased with increasing successional age, although the abundance of the latter in early midsuccession was lower than that in late midsuccession.

1 4 2

Serai Stage

Species Ruderal Early Early mid Late mi a

Arthaldeus pascuellus 0 12 1 0

Psammotettix confinis 18 69 3 0

Doratura sylata 1 1 12

Macrosteles laevis 224 84 2 1

TOTAL 243 166 8 13

Table 4.5a

Serai Stage

Species Ruderai Early Early mid Late mid

Adarrus ocellaris 45 139 548 243

Cicadula persimilis 0 1 0 1

Dipiocoienus abdominalis 0 0 1 0

Recilia coronifera 6 6 59 219

Aphrodes albifrons 0 0 1 7

Aphrodes bicinctus 2 6 23 21

TOTAL 53 152 631 491

Table 4.5b

Table 4.5 Adult abundance of Cicadellidae specialising on (a) Agrostis spp,. (b) Holcus spp in different serai stages.

Fig 4.21 Mean absolute abundance by (a) host plant family of Cicadellidae excluding Typhlocybinae (b) host plant species of Cicadellidae excluding Typhlocybinae (c) host plant family of Typhlocybinae and (d) host plant species of Typhlocybinae in different serai stages (R = ruderal, E = early succession, EMS = early midsuccession, LMS = late midsuccession, L = late succession). Bars are standard errors.

ABSO

LUTE

ABUN

DANC

E AB

SOLU

TE AB

UNDA

NCE

1 4 3

FIG 4.21CICADELLIDAE(phloem feeding species)

a)ABSOLUTE ABUNDANCE BY HOST PLANT FAMILY

600

300

400

300

200

100

i i • * • oR B RMS LM 3 L

SERAL STAGETYPHLOCYBINAE

c)ABSOLUTE ABUNDANCE BY HOST PLANT FAMILY

41200 41100 41000 40900

1000 900 100 700 600 300 400 300 200

100 0

R B CMS LM S L R B CMS LM 3 L

700 -

600 -

300 -

400 -

300 -

200 -

100 -

d)ABSOLUTE ABUNDANCE BY HOST PLANT SPECIES

i 1

b)ABSOLUTE ABUNDANCE BY HOST PLANT SPECIES

SERAL STAGE

1 4 4

Absolute abundance by host plant family and species of non-woody plant feeders was greater than that of woody plant feeders regardless of their mode of feeding (Fig. 4.22). However, there was no significant difference between the absolute abundance by host plant family of woody and non-woody plant phloem-feeding species (F^ = 0.5009, P > 0 .05),whereas all other comparisons were significantly different (Typhlocybinae: abhf, F^ = 110.3, P < 0.001; phloem­feeding Cicadellidae F^ = 8.097, P < 0 .05).

4.4 DISCUSSION

The absolute abundance of insect groups varied between serai stages. However, the two measures of abundance (by host plant family and host plant species) did not always show consistent trends. Absolute abundance by host plant family ofCicadellidae, Heteroptera and Curculionoidea was greatest on the ruderal stage and least on birch, but only the former decreased progressively with increasing successional age, while forabundance by host plant species the Psyllidae also showed this trend. The lack of consistent trends in absolute abundance throughout the season was not unexpected since gross changes in host plant chemistry are known to occur (Feeny, 1970; Lawton, 1976; Thompson & Price, 1977). However, despite seasonal fluctuations, absolute abundance was generally lowest in late succession and highest during the early years of succession.

A progressive decline in absolute abundance with increasing successional age of the habitat is unlikely for two reasons; firstly, there were several plant species and genera common to two or more serai stages (section 3 .3 ). Such species would be likely to be consistent in their chemical defences and their relationship with herbivores between stages. Secondly, certain insect species may be particularly abundant on a single site during a single year. This could occur as a result of a decrease in the defensive chemistry of the plant, an increase in nutritional value of a plant/patch, favourable microenvironment for reproduction and survival, decreased predation, or alternatively the species could be in a boom part of a cycle.

Fig 4.22 Mean absolute abundance by (a) host plant family of Cicadellidae excluding Typhlocybinae, (b) host plant species of Cicadellidae excluding Typhlocybinae, (c) host plant family of Typhlocybinae and (d) host plant species of Typhlocybinae on woody and non-woody plants (hatched columns = woody, clear columns = non-woody plants). Bars are standard errors.

AB

SOL

UT

E A

BU

ND

AN

CE

A

BSO

LU

TE

AB

UN

DA

NC

E

1 4 5

FIG 4.22

CICADELLIDAE(phloem feeding species)a)ABSOLUTE ABUNDANCE b)ABSOLUTE ABUNDANCEBY HOST PLANT FAMILY by HOST PLANT SPECIES

PLANT TYPE

TYPHLOCYBINAEc)ABSOLUTE ABUNDANCE BY HOST PLANT FAMILY

d)ABSOLUTE ABUNDANCE BY HOST PLANT SPECIES

PLANT TYPE

146

Clearly a larger data set would clarify such anomalies. Among the herbivorous groups examined, it was perhaps the Heteroptera which were least likely to show any pattern, since within this group species show a range of trophic relations, including folivorous species, seed and flower-feeders and partial predators (Southwood S Leston, 1959; V/etton & Gibson, 1987). Such potential for polyphagy or omnivory would tend to make patterns of abundance based on plant chemistry less consistent that in totally folivorous groups.

Lawton £ McNeill's (1979) hypothesis predicts a difference between the absolute abundance of herbivores of typical early successional plants and that of herbivores of late successional plants, ie trees. Effectively, this is a difference in the absolute abundance of herbivores feeding on plants defended by qualitative and those defended by quantitative defences. V/hen tested it was seen that with one exception, there were significantly more herbivores/m2 leaf area on non-woody plants than on woody plants. The group which diverged from this trend was the phloem-feeding Cicadellidae, which when analysed by host plant family were not significantly more abundant on non-woody plants than woody plants. This result is of interest, since it may reflect a greater effect of host plant on mesophyll- feeding Cicadellidae than on phloem-feeding Cicadellidae.Consideration of the biochemistry of tannins lends support to this hypothesis. Condensed tannin is probably stored as a complex in structural protein and is usually associated with organelles or cells walls, while hydrolysable tannin is usually stored in vacuoles. Membranes tend to be non-permeable to tannins due to their size and relative polarity (Zucker, 1983) so, unless active transport occurs (which is unlikely), the concentration of tannin in phloem would probably be very low or even non-existent.

It is difficult to explain the difference in the pattern of absolute abundance with serai stage observed in the Cicadellidae and Delphacidae, since the two groups are close taxonomically and ecologically. However, some ideas are explored in Chapter 5.Grasses, the food of both groups, are defended by a mixture of qualitative and quantitative defences: alkaloids are present in

1 4 7

some species when young (Harley & Thorsteinson, 1967) and silica may be present in older individuals (Crawley, 1983). From the standpoint of a herbivorous insect, grasses may be as apparent (sensu Feeny) as trees, since clones of stoloniferous grasses eg . Holcus mollis may cover many acres and be of considerable age (Harper, 1977). Grasses therefore seem to lie in the middle of the qualitative-quantitative defence spectrum but are not considered in detail by Feeny (1976), Rhoades & Cates (1976) or Lawton & McNeill (1979). In the present study, the Heteroptera enabled this to be considered. The abundance of Heteroptera decreased in the order herbaceous dicotyledons > grass > trees with the absolute abundance of grass-feeding species being closer to that of tree-feeding species than to that of species feeding on herbaceous dicotyledon plants. These results support the position of grasses as intermediate between qualitatively-defended early successional plants and quantitatively-defended late successional plants.

There were differences in absolute abundance of grass-feeding species between serai stages, with the absolute abundance of both specialist Holcus and Acjrostis-feeding species being greatest in the ruderal stage. This difference could be due to reduced predation, to the reduced action of chemical defences, or to differences in the nutritional status of the soil/plant. After disturbance and the commencement of succession, soil nutrients may change in several ways. In nutrient-rich soils, nutrients may not accumulate during succession and may actually be lost (Aarrssen & Turkington, 1985) while in nutrient-poor soils, such as those at Silwood Park, there may be a period of nutrient accumulation ( Inovxye, Huntley, Tilman, Tester, Stillwell5 Zinnel, 1987). Also, in tropical forests where soils are generally extremely nutrient-poor, there is a pulse of nutrients immediately after disturbance which rapidly falls away (Vitousek6 Walker, 1987). Nitrogen is generally the limiting nutrient for plant growth (Tilman, 1988) and both total and available nitrogen have been reported to increase during succession (Til man, 1988). Although no measures of nutrient status of the soil have been made in the successional sere at Silwood Park, the small spatial scale and relatively small age differences

1 4 8

between stages make it unlikely that there would be substantial differences in the concentration of nutrients. However, the lower levels of plant competition in the ruderal stage may increase the amount of available nutrients. Such a suggestion would fit with the pattern of absolute abundance of specialist feeders on Holcus and A grostis, since these were very abundant on the ruderal sites with little difference in abundance on the older sites.

Although this thesis generally assumes ecological andevolutionary pressures to be equal on all species within a group, it must be realised that the absolute abundance of species may be subject to many different selective pressures. The major conclusion from the analysis of absolute abundance of herbivore species feeding on plant families at different serai stages is simply that qualitative defences cannot be lumped together and assumed to have the same effect on herbivore populations. The differences in absolute abundance of species feeding on dicotyledonous plant families, both within and between serai stages, stresses the different relationship between herbivore and host plant, and how these can be affected by a multiplicity of factors.

In conclusion, it seems that Lawton & McNeill (1979) were correct, and that the absolute abundance of herbivore species feeding on plants defended by qualitative defences is greater than that of species feeding on plants defended by quantitative defences. However, it is more difficult to establish why absolute abundance varies between different serai stages of predominantly qualitatively defended plants. Variation in predation pressures and soil nutrient availability is certainly worthy of further investigation.

1 4 9

CHAPTER FIVE

VEGETATION STRUCTURE AND THE INSECT COMMUNITY

5.1 INTRODUCTION

The main aim of this chapter is to investigate the effect and importance of small-scale differences in community attributes on insect herbivore abundance and species richness. Particular attention has been focussed on the importance of plant species and community architecture or structure. Plant architecture has two major attributes, the size and/or spread of structures and their variety. Since only the size and spread of plant structures is considered here, it is preferable to refer to plant structure. These attributes of the community are best measured by a foliage height index (Lawton, 1978), such as that utilised by Murdoch, Evans S Peterson (1972) and Stinson & Brown (1983).

Plant architecture is important as it permits greater niche diversification for, inter alia competitor and predator avoidance, and hence architecturally more complex plants should support more herbivore species (Lawton, 1983). This has been shown to be the case by Lawton & Schroder (1977), as herbivore species richness on different plant growth forms declines in the order, trees > weeds and other annuals > monocotyledons (excluding grasses). Many studies have considered changes in architecture on herbivore species richness, and found good positive correlations between plant architecture and herbivore species richness (Cameron, 1972; Denno, 1977, Lawton, 1978; Morris, 1971, 1979, 1981; Morris & Lakhani, 1979; Murdoch et al, 1972; Niemela & Haukioja, 1982; Niemela, Tahvanainen, Sorjo\oen, Hokkaren & Neuvonnen, 1982; Stinson & Brown, 1983). These studies tend to fall into one of two categories; either they are based on literature reviews of plant attributes and of herbivore host plant specificity and occurrence (both of which may be subject to error), or they utilise seasonal changes in plant architecture as "natural experiments". Such methodology does not take into account the many other seasonally fluctuating

1 5 0

factors which may affect herbivore abundance and diversity, e .g . plant nutritional quality, plant chemical defences, leaf toughness, temperature, predator and competitor abundance. Few studies have considered the effect of small scale variation in plant architecture on herbivore abundance and diversity. Despite demonstrating that the species diversity of Homoptera correlated with foliage height diversity and mean vegetation height between fields, Murdoch et a[ (1972) found only poor correlation between plant diversity and structure and insect diversity in small scale quadrats within a field. Two other studies (Cornell 8 Washburn, 1979 and Fowler, 1985) report little difference in herbivore species diversity between architecturally simple and complex system s. The aim of this chapter is two-fold: firstly to examine the importance of various community attributes, including host plant structure and the structure of the surrounding vegetation, on the abundance and species richness of insect herbivores on a single date in each of four serai stages, and to compare patterns between them, and secondly to test the null hypothesis that the absolute abundance of individual species does not differ between serai stages. If absolute abundance is determined solely by the relationship between the herbivore and the chemical defences of its host plant, then there should be no differences in absolute abundance between serai stages. However, if this relationship is modified in some way by the surrounding community then differences in absolute abundance could occur. Work at the species level allowed some comparisons between Cicadellidae and Delphacidae to be made in an attempt to understand their different relationships with their host plants. Finally, this chapter tests the nullhypothesis thab absolute abundance of birch-feeding insects does not vary between upper and lower canopy. Studies by Claridge, Edington & Murphy (1968) and Fowler (1985) conclude there is no overall vertical stratification of species in a birch canopy, although individual species may show preferences for different parts of the canopy. Fowler (1985) demonstrated that Operophtera (Lepidoptera: Geometridae), Epinotia (Lepidoptera: Tortricidae) and Euceraphis spp (Hemiptera: Aphididae) showed a significant preference for upper canopy, whereas six other species, Oncopsis spp (Homoptera: Cicadellidae), Apoch eima

1 5 1

pilosaria, Erannis defoliaria, Agriopis spp (Lepidoptera: Geometridae), Coleopihera serratella (Lepidoptera: Coleophoridae) and Eriocrania spp (Lepidoptera: Eriocraniidae) showed nopreference. In a comparable study on beech, Phillipson & Thompson (1983) recorded greatest herbivore damage in the lower canopy, where 75-85% of leaves were attacked and accounted for 35% of the total herbivore damage.

5.2 METHODS

General field methods are described in Chapter 2. The abundance of adults of the most commonly occurring species in each subplot was correlated with several community attributes. Only species for which more than 15 individuals were recorded from a single site during the August 1985 sample were included in the analysis. August was selected since peak insectabundance and species richness generally occurred during that month (see section 3 .4 ). The late successional site was omitted from this analysis. The community attributes considered were host plant species leaf area, host plant family leaf area, total leaf area of subplot, mean height of host plant species, mean height of host plant family, overall mean height of subplot, number of leaves in host plant family, number of leaves in subplot and oC-diversity of plants in subplot. The measurement of these parameters is described in Chapter 2. Data for the mean height index were gathered by using a point quadrat frame 50cm in length with 10 equally spaced pins. Each pin (3mm diameter) was marked at intervals of 2, 4 , 6, 8 and 10cm and then at successive 5cm intervals from soil level to the maximum height of the vegetation. A single frame was randomly placed in each subplot in August 1985. A measure of vegetation height, based on a weighted mean height of touches, was derived from:

where h = midpoint of class 'i1, n = number of touches of height class 'i1, N = number of height classes represented in the sample.

N

i = 1

1 5 2

The non-normality of the insect abundance data necessitated the use of Spearman's Rank Correlation. This non-normality of the data violated several assumptions of multiple regression techniques, which would otherwise have been utilised. Since it was likely that many of the community attributes were themselves related, Spearman's Rank Correlation was used to test for any autocorrelation between the variables which could affect interpretation of the resu lts. The species richness of Cicadellidae, Delphacidae, Heteroptera and Curculionoidea in each subplot during August 1985 was also correlated with the community attributes. A final analysis considered the relationship of species richness of each insect group with that of each other insect group. The analyses of insect speciesrichness utilised Pearson's Correlation Coefficient.

In order to test for differences in absolute abundance of a single species between serai stages the most abundant species occurring on all of the four younger serai stages were analysed usingGLIM, as described in Chapter 2. Patterns of adult abundancebetween serai stages were compared with those of absolute abundance. Analyses comparing these parameters statistically would not be valid as adult abundance is inherent in the calculation of absolute abundance. Data was pooled over two years and dates. Differences in absolute abundance of birch herbivores between the upper and lower birch canopy were assessed by GLIM where appropriate, however, Kruskall-Wallis non-parametric one-way ANOVA was utilised for the analysis of canopy differences of Heteroptera, and for single speciesresponses. The absolute abundance of species of Cicadellidae overwintering as eggs and those overwintering as adults were compared using GLIM (data on overwintering strategies was taken from VValoff, 1981).

153

5.3 RESULTS

5 .3 .i Vegetation structure and small scale variation in herbivore abundance and species richness

Weevil abundance on the ruderal site was positively correlated with most community attributes, with host plant leaf area and mean height being particularly important. Abundance of Cassida vittata was also positively related to these two attributes, although abundance of Auchenorrhyncha displayed more varied responses to community attributes (Table 5 .1a). Host plant leaf area was also strongly correlated with weevil abundance in early succession (Table 5 .1b ). Mean height was important to Apion dichroum, but not to A apricans or A hookeri. However, total leaf number, total leaf area and plant oC-diversity were generally poorly correlated with weevil abundance, and no single community attribute was significantly related to the abundance of the Auchenorrhyncha species considered. The abundance of Apion species in early midsuccession was also positively correlated with host plant species area, mean height and leaf number. However, abundance of the generalist weevil, Sitona lineatus was not significantly correlated with any community attribute. As on the younger sites, there appeared to be little consistency in factors influencing Auchenorrhyncha abundance (Table 5 .1c). The abundance of Dicranotropis hamata and to a lesser extent Adarrus ocellaris was significantly correlated with host plant leaf area, and Zyginidia scutellaris with host plant mean height. On the late midsuccessional site no weevil species was sufficiently abundant to permit analysis, although several Heteroptera species were. Factors affecting Heteroptera abundance were generally similar to those for the weevils on the younger sites, in that abundance was significantly correlated with host plant area and mean height, with the exception of the grass-feeding species Stenodema laevigatum (Table 5 .1d). The abundance of Auchenorrhyncha showed similar patterns to those for other sites. The abundance of A^ ocel laris and Stenocranus minutus was significantly correlated with host plant leaf area, while host plant mean height was also important for S _ minutus. Euscelis incisus showed significant correlation with leaf number

Table 5.1 Spearman's Rank Correlation Coefficients for adult abundance of common herbivore species in subplots with several measured vegetation attributes during August 1985 in (a) ruderal, (b) early succession,(c) early midsuccession, (d) late succession. * P < 0.05, ** P < 0.01, *** P < 0.001.

SPECIES

Host plant species leaf area

Host plant family leaf area

Total subplot leaf area

COMMUNITY

Host plant species mean height

ATTRIBUTES

Host plant family mean height

Subplotmeanheight

Number of leaves in host family

Number of leaves in subplot

Plant

©(diversity

Apion 0.05095 0.5183 0.5032 0.4872 0.4645 0.4781 0.4347 0.3979 0.2742assimile *** *** *** ** ** + * ** *

Apion 0.3486 0.3716 0.2747 0.4974 0.45 0.3322 0.3241 0.3819 0.3473apricans ♦ * *+* ** * * * *

Cassidavittata

0.3548*

- 0.0051 0.4427**

- 0.0179 - 0.1111 -0.0803

Macrosteleslaevis

-0.2777 0.0678 0.3670*

0.0852 0.2754 0.3172*

-0.2461 0.3497*

0.0212

Zyginidiascutellaris

0.1126 0.2024 -0.1423 0.1098 0.0612 0.0114 0.4341**

-0.2381 0.0754

Dicranotropishamata

0.1607 -0.0056 0.1780 0.0302 0.2763 0.3507*

0.0359 0.2888 -0.1898

Table 5.1a (Ruderal)

154

COMMUNITY ATTRIBUTES

Host plant species leaf area

Host plant family leaf area

Total subplot leaf area

Host plant species mean height

Host plant family mean height

Subplotmeanheight

Number of leaves in host family

Number of leaves in subplot

Plant

oUiiversity

Apionassimile

0.5306***

0.5014 0.3802*

0.3673*

0.4123**

0.3656*

0.4121**

0.2785 0.1695

Apionapricans

0.7232 0.5609***

0.2811 0.5363***

0.3984*+

0.2107 0.4955#** 0.2437 0.2947 *

Apiondichroum

0.4487**

0.4020**

0.1390 0.3403*

0.3723 ' *

0.5284***

0.4087 0.2214 0.1914

Apionhookeri

0.7382***

- 0.3157*

0.6629*#*

- 0.2642 0.3587*

0.3223*

0.4254**

Jav.esellapellucida

- 0.0170 0.0581 - 0.0219 0.0275 -0.0975 -0.0686 0.1939

Euscel \s incisus

0.0245 0.1358 “ 0.813 0.1788 -0.0538 -0.0133 -0.0542

Table 5.1b (Early succession)

155

SPECIES COMMUNITY ATTRIBUTES

Host plant species leaf area

Host plant family leaf area

Total subplot leaf area

Host plant Host plant species mean family mean height height

Subplotmeanheight

Number of leaves in host family

Number of leaves in subplot

Plant

cCdiversity

Apionassimile

0.6091***

0.3737**

0.1677 0.6386 - 0.0309 0.4178*♦

0.3569«

0.3750*♦

Apionapricans

0.7453 0.4163**

0.1016 0.7133**+

- 0.1291 0.3862 0.2362 0.2268

Sitonalineatus

- 0.2307 -0.0900 - - 0.1577 0.2119 0.0741 0.2343

Adarrusocellarus

0.3617*

0.2301 0.1638 -0.0945 -0.022 0.0122 0.0445 -0.1040 0.0873

Mocydiopsisparvicauda

- -0.0671 -0.3413 - -0.0853 0.0661 -0.0795 -0.0789 0.1352

Reciliacoronifera

-0.0402 -0.0203 -0.1803 0.1271 0.1683 0.0539 0.3557 0.1481 -0.1624

Zyginidiascutellaris

0.1399 0.2206 0.2053 0.5031*+*

0.2711 0.1588 0.0588 0.063 0.2974

Dicranotropishamata

0.4496**

0.4715+*

0.3341*

0.0149 0.0183 0.1983 0.2938 -0.0295 -0.0753

Javesellapellucida

- 0.1226 0.1124 - 0.2619 0.3434*

0.2648 0.3159*

0.3599+

Table 5.1c (Early midsuccession)

156

SPECIES COMMUNITY ATTRIBUTES

Host plant species leaf area

Host plant family leaf area

Total subplot leaf area

Host plant Host plant species mean family mean height height

Subplotmeanheight

Number of leaves in host family

Number of leaves in subplot

Plant

^diversity

Stenodemalaevigatum

- 0.1982 0.2415 - 0.0661 0.0804 0.1721 0.1787 0.1376

Phytocorisvaripies

- 0.3372*

0.3792*

- 0.4561**

0.4989**+

0.3051* 0.3092♦

0.1458

Ishnodemussabuleti

0.7329+**

0.2385 0.2983#

0.5022*+*

0.3947**

0.3864**

0.097 0.0961 0.2022

Tingisampliata

0.5424 - 0.2732 0.5357 - 0.2489 0.4456**

0.2269 0.1688

Zyginidlascutellaris

0.045 0.043 0.2146 0.2490 0.0061 0.0293 0.1695 0.2991* -0.0473

Stenocranusminutus

0.428**

0.1976 0.1159 0.4666**

0.2093 0.2539 0.1899 0.2254 0.1719

Dicranotropishamata

0.1237 0.032 0.0525 0.0955 -0.0238 0.1275 0.2481 0.1848 0.0722

Adarrusocellarus

0.333*

0.248 0.2880 0.1714 0.0247 0.0638 0.1894 0.2724 0.1423

Eusceli‘sincisus

- 0.2498 0.3005 - 0.2171 0.2221 0.3151*

0.3611*

0.2364

Mocydiopsisparvicauda

- 0.2181 0.2211 - 0.0212 0.0277 0.2537 0.1230 0.0128

Table 5.1d (Late midsuccession)

157

1 5 8

on this site (Table 5 .1d ). Insect species richness was only correlated with two community attributes (Table 5.2) both of these occurring on the ruderal site.

As might be expected there was a high degree of autocorrelation between plant community attributes. These have been assessed for host plants of the individual dominant herbivores, and were especially evident amongst the Leguminosae. On all sites, host species area of Legume-feeding species was generally significantly positively correlated with all other variables (Table 5 .3a -c). Attributes of the grasses also demonstrated autocorrelation. On the ruderal site , the three measures of leaf area were highly correlated, as were the measures of mean height (Table 5 .3d ). In early succession, family leaf area and mean height were highly correlated with total leaf area and mean height respectively (Table 5 .3 e ). The three measures of leafarea were also autocorrelated in early midsuccession, but were not related to any measure of structure (Table 5 .3 f). Total structure was highly correlated with grass structure on this site and in late midsuccession. Both lanatus and glomerata leaf area in late midsuccession were correlated with most other community attributes (Table 5 .3 g ) . In contrast to the majority of resu lts, no measured attributes of Spergula arvensis were autocorrelated (Table 5 .3 h ). However, leaf area ofTripleurospermum inodorum in early succession was significantly correlated with all measured community attributes, and that of Cirsium arvense in late midsuccession with all community attributes except mean height (Tables 5 .3i—j).

5 .3 .ii Variation in absolute abundance of species between different serai stages

Absolute abundance by host plant family of three species of Apion and Sitona lineatus differed significantly between serai stages, whereas the absolute abundance of Sitona sulcifrons and Sitona hispidus was similar between serai stages (Figs 5 .1 a -f). Based on host plant species the absolute abundance of A. assimile and A apricans also differed significantly between serai stages, although that of A^ aethiops showed no significant

159

Coeiunity attributes

Serai Insect Leaf area Grass Plot Grass Ho, of Ho, of Plantstage Group of plot leaf area aean

heightlean

heightleaves in plot

grassleaves

ocdiversity

Heteroptera 0,0007 - -0,165 0,1287 0 , 4 7 0 6 * * *Ruderal Curculionoidea 0,1498 - 0,0802 - 0,2611 - 0,1606

Cicadeilidae 0,1809 -0,1685 -0,1756 -0,0435 0.2705 -0,2853 0,2784Delphacidae 0,3719* 0,2015 -0,2202 -0,1592 0,2106 0,0275 0,1347

Heteroptera - 0,18S7 _ 0,1150 -0.0377 _ 0,1398Early Curculionoiaea 0,0555 - 0,1107 - -0,0516 - -0,1959

Cicadeilidae 0,1310 0,1122 -0,1204 -0.0506 -0,2104 -0,0572 0,0796Delphacidae 0,1198 0,0333 -0,2807 -0,1908 -0,1740 -0,1742 -0,0058

Heteroptera 0,0240 -0,0821 _ -0,0755 . 0,0154Early Curculionoidea -0.0368 - -0,1340 - 0,0208 - -0,0299Hid Cicadellidae -0,1295 -0,0702 0,0869 0,0962 -0,0547 -0,0638 0,0064

Delphacidae -0,1618 0,0640 -0,0484 -0,0884 -0,1535 0,2989 -0,0447

Heteroptera 0.1794 0.2504 0,0900 . -0,0446Late Curculionoidea 0,3146 - 0,1673 - 0,0358 - 0.0670aid Cicadellidae 0,1023 -0,0601 -0,2704 -0,2658 0.2719 -0,0281 -0,0976

Delphacidae -0,1333 -0,1435 0,1234 0,0145 -0,1069 -0,1415 -0.0780

Table 5.2 Pearson's Correlation Coefficient for species richness of Heteroptera, Curculionoidea, Cicadeilidae and Delphacidae in subplots with several measured vegetation attributes during August 1985 in ruderal, early succession, early midsuccession and late midsuccession. * P < 0.05, ** P < 0.01, *** P < 0.001.

Table 5.3 b Correlation coefficient for autocorrelation between vegetation attributes for host plants in subplots during August 1935. Separate tables for the host plant of hervibores in each serai stage; (a) Trifolium pratense on ruderal site; (b) Trifolium pratense and T rifolium spp (in parenthesis) in early succession; (c) T rifolium pratense and T rifolium spp (in parenthesis) in early midsuccession; (d) Agrostis capillaris and Holcus lanatus (in parenthesis) on ruderal site; (e) grasses in early succession; (f) Holcus lanatus in early midsuccession; (g) Holcus lanatus and Dactyli s glomerata (in parenthesis) in late midsuccession;(h) Spergula arvensis on ruderal site;(i) Tripleurospermum inodorum in early succession;(j) Cirsium arvense in late midsuccession. * P < 0.05, ** P < 0.01, *** P < 0.001.

H a s t

s p e c i e s

l e a f a r e a

H o s t

F a m i1 y

l e a f a r e a

T o ta l

s u b p l o t

l e a f a r e a

H a s t

s p e c i e s

m ean h e i g h t

Fam i 1 y

m ean

h e i g h t

T o ta l

mean

h e i g h t

Na. f a m i l y

l e a v e s

T o ta l no .

o f l e a v e s

P I a n t

d i v e r s i t y

H o s t s p e c i e s

l e a f a r e a

H o s t F a r a i1 y

l e a f a r e a

0 . 9 6 1 4

t i l

T o ta l s u b p lo t

l e a f a r e a

0 . 9 1 9 8

I I I

0 . 8 7 2 6

I I I

H o s t s p e c i e s

mean h e i g h t

0 . 6 6 8 5

i l l

0 . 6 6 9 3

H I

0 . 5 7 9 7

i l l

H o s t F a m i l y

m ean h e i g h t

0 . 6 3 4 0

I I I

0 . 6 4 0 3

I I I

0 . 5 4 0 0

I I I

0 . 9 1 2 6

I I I

T o t a l m ean

h e i g h t

0 . 3 0 9 2

l

0 . 2 5 1 2

1

Q . 1 7 5 3 0. 4 4 6 6

I I

0 . 3 8 1 3

l

No. f a m i l y

l e a v e s

0 . 9 3 3 8

i l l

0 . 9 2 1 8

i n

0 . 8 4 0 8

I I I

0 . 5 8 2 8

h i

0 . 6 4 4 2

I I I

0 . 2 1 0 5

T o ta l no.

o f l e a v e s

0 . 7 0 6 7

I I I

0 . 6 3 2 8

i l l

0 . 6 1 0 1

I I I

0. 4 4 3 0

I I

0 . 5 0 7 2

i l l

0 . 0 5 9 0 0 . 7 9 5 4

I I I

P l a n t

d i v e r s i t y

0 . 0 0 8 8 0 . 0 1 0 2 - 0 . 0 1 2 9 0 . 2 3 1 9 0 . 2 5 0 2 0 . 0 6 1 4 0 . 0 3 6 7 - 0 . 2 9 9 0

H o s t

s p e c i e s

l e a f a r e a

H o s t

F a m i l y

l e a f a r e a

T o ta l

s u b p l o t

l e a f a r e a

H o s t

s p e c i e s

m ean h e i g h t

F a a i 1 y

m ean

h e i g h t

T o ta l

mean

h e i g h t

Ho. f a m i l y

1 e a v e s

I c t a l no.

c r l e a v e s

F I a n t

a i v e r s i t y

H o s t s p e c i e s

l e a f a r e a

H o s t F a m i l y

l e a f a r e a

T o ta l s u b p l o t

l e a f a r e a

- 0 . 0 1 4 0

H o s t s p e c i e s

mean h e i g h t

0 . 2 1 6 3 Q. 0 4 1 9

H o s t F a m i l y

mean h e i g h t

T o t a l m ean

h e i g h t

0 .0 6 1 1 0 . 1 7 3 5 0 . 2 9 2 8

No. f a m i l y

l e a v e s

T o ta l n o .

o f l e a v e s

- 0 . 1 5 9 2 0 .6 1 0 1 0 . 1 8 7 6 0 . 0 5 9 0

P l a n t

d i v e r s i t y

0 . 0 9 2 7 - 0 . 0 1 2 9 0 .1 6 2 1 0 . 0 6 1 4 -0 . 2 9 9 0

Table 5.3b

160

H o s t

s p e c i e s

l e a f a r e a

H o s t

Fam i 1 y

l e a f a r e a

T o ta l

s u b p l o t

l e a f a r e a

H o s t

s p e c i e s

n e a n h e i g h t

F a m i1 y

m ean

h e i g h t

T o ta l

m ean

h e i g h t

No. f a m i l y

1 e a v e s

T o ta l n o .

o f l e a v e s

P I a n t

d i v e r s i t y

H o s t s p e c i e s

l e a f a r e a

H o s t F a n i l y

l e a f a r e a

- 0 . 2 1 9 9

( 0 . 6 7 9 7 )

T o t a l s u b p lo t

l e a f a r e a

- 0 . 6 3 1 3

I I I

( 0 . 6 0 3 4 )

0 . 5 2 7 0

I I I

H o s t s p e c i e s

tie a n h e i g h t

0 . 3 4 3 9

(0 . 4 9 3 2 )

0 . 3 1 2 1

( 0 . 2 3 1 5 )

- 0 . 1 3 1 2

( 0 . 1 6 7 2 )

H o s t F a n i l y

n e a n h e i g h t

- 0 . 2 9 5 7

(0. 4 1 9 9 )

0 . 1 1 5 3 0 . 2 6 7 6 - 0 . 1 0 2 1

( 0 . 3 9 1 4 )

T o t a l m ean

h e i g h t

0 . 3 2 8 3

( 0 . 3 5 0 8 )

0 . 0 1 1 3 0 . 1 7 5 3 - 0 . 1 7 8 1

( 0 . 3 4 1 6 )

0 . 7 8 3 4

I I I

No. fa m i 1 y

l e a v e s

0 . 5 4 5 2

H I

( 0 . 0 7 1 5 )

0 . 5 7 0 7

I I I

- 0 . 1 4 7 4 0. 2 4 9 5

l

( 0 . 1 3 4 2 )

- 0 . 1 2 8 4 - 0 . 1 9 2 9

T o t a l no.

o f l e a v e s

- 0 . 2 7 2 0

( 0 . 1 6 0 5 )

0 . 0 1 1 6 0 .6 1 0 1

H I

0 . 1 0 1 3

( 0 . 1 1 0 4 )

0 . 0 5 4 6 0 . 0 5 9 0 - 0 . 2 1 7 9

P l a n t

d i v e r s i t y

- 0 . 2 2 1 7

( 0 . 0 5 7 3 )

- 0 . 1 3 3 9 - 0 . 0 1 2 9 0 . 0 1 3 4

( 0 . 1 0 0 3 )

0 . 1 2 2 8 0 . 0 6 1 4 - 0 . 2 8 9 7 - 0 . 2 9 9 0

Table 53c

H o s t

s p e c i e s

l e a f a r e a

H o s t

F a r a i1 y

l e a f a r e a

T o ta l

s u b p l o t

l e a f a r e a

H o s t

s p e c i e s

n e a n h e i g h t

Fam i 1 y

m ean

h e i g h t

T o ta l

m ean

h e i g h t

No. f a m i l y

1 e a v e s

T o t a l na.

o f l e a v e s

P I a n t

d i v e r s i t y

H o s t s p e c i e s

l e a f a r e a

H o s t F a m i l y

l e a f a r e a

l 0 . 6 1 1 9

l l

T o t a l s u b p l o t

l e a f a r e a

0 . 5 1 1 0

I I I

10. 4 0 4 2 )

I I

H o s t s p e c i e s

mean h e i g h t

0 . 5 9 7 2

I I I

1 0 . 1 1 4 4 )

0 . 2 4 1 8

( 0 . 0 6 9 2 )

H o s t F a n i l y

n e a n h e i g h t

0 . 5 1 3 2

I I I

( 0 . 4 1 2 1 )

I I I

0. 4 3 1 9 0 . 8 4 2 3

T o ta l m ean

h e i g h t

0. 458 1

I I I

( 0 . 1 6 0 4 )

- 0 . 0 2 7 3 0 . 1 9 1 7

( 0 . 0 7 7 7 )

0 . 4 3 2 1

No. f a m i l y

1 e a v e s

I I 0 . 4 8 3 9

( 0 . 6 5 7 1 )

I I I

0 . 0 8 8 9 0 .1 1 5 0

( 0 . 1 7 1 8 )

0 . 5 9 2 7 0 . 0 1 7 0

T o t a l no.

o f l e a v e s

I I 0 . 4 9 2 3

( 0 . 3 4 8 8 )

l

0. 4 2 3 8 0 . 1 8 0 3

( 0 . 0 5 2 0 )

0 . 1 2 0 0 0. 1401 0 .3 5 8 1

P l a n t

d i v e r s i t y

0 . 3 3 7 6

i

( - 0 . 2 1 7 8 )

- 0 . 2 4 3 5 0 .2 7 7 7

( 0 . 0 5 0 3 )

0 . 0 2 4 1 - 0 . 0 9 6 6 - 0 . 0 5 5 3 - 0 . 1 4 0 5

Jflble 5.3d

161

H o s t

s p e c i e s

l e a f a r e a

H o s t

Fam i 1 y

l e a f a r e a

T o ta l

s u b p l o t

l e a f a r e a

H o s t

s p e c i e s

m ean h e i g h t

F a m i l y

mean

h e i g h t

T o ta l

m ean

h e i g h t

No. fam i 1 y

1 e a v e s

T o ta l no.

o f l e a v e s

P I a n t

d i v e r s i t y

H o s t s p e c i e s

l e a f a r e a

H o s t F a m i l y

l e a f a r e a

T o t a l s u b p lo t

l e a f a r e a

0 . 3 3 9 0

H o s t s p e c i e s

m ean h e i g h t

0 . 7 1 7 3

H i

0 . 0 7 2 1

H o s t F a m i l y

m ean h e i g h t

T o t a l m ean

h e i g h t

0. 4 8 5 3

I I I

- 0 . 0 2 7 3 0 . 3 9 0 4

I I

No. f a m i l y

l e a v e s

0 . 6 1 6 4

I I I

- 0 . 0 2 3 3 0 .3 0 9 1 0. 2 4 0 5

T o t a l n o .

o f l e a v e s

0 . 4 5 9 2

I I I

0 . 4 2 3 8

l l

0 . 1 6 7 4 0 .1 4 0 1

P l a n t

d i v e r s i t y

0 . 5 0 1 1

I I I

- 0 . 2 4 3 5 0 . 3 5 3 9

1

-0 . 0 9 5 6 - 0 . 1 4 0 5

Table 5.3e

H o s t

s p e c i e s

l e a f a r e a

H o s t

Fam i 1 y

l e a f a r e a

T o ta l

s u b p l o t

l e a f a r e a

H o s t

s p e c i e s

m ean h e i g h t

F a m i l y

m ean

h e i g h t

T o ta l

m ean

h e i g h t

No. f 3T.i y

1 e a v e s

T o ta l no.

o f l e a v e s

P I a n t

d i v e r s i t y

H o s t s p e c i e s

l e a f a r e a

H o s t F a m i l y

l e a f a r e a

T o t a l s u b p l o t

l e a f a r e a

0 . 8 7 0 1

I I I

H o s t s p e c i e s

mean h e i g h t

H o s t F a m i l y

m ean h e i g h t

0 .0 1 4 1 0 . 0 4 6 6

T o t a l m ean

h e i g h t

- 0 . 1 0 7 8 -0 . 0 9 0 7 0 . 7 5 0 7

H I

No. f a m i l y

l e a v e s

0 .8 6 5 1

I I I

0 . 7 5 6 9

I I I

0 . 0 4 6 6 -0 . 0 9 0 7

T o t a l no.

o f l e a v e s

0 . 3 1 7 8 0. 4 2 3 8

I I

- 0 . 0 8 1 4 0. 1401 0 . 4 4 3 2

I I

P l a n t

d i v e r s i t y

- 0 . 1 1 0 3 0 . 0 2 6 3 -0 . 0 9 5 6 - 0 . 2 9 5 5 - 0 . 1 4 0 5 162

H o s t

s p e c i e s

l e a f a r e a

H o s t

F a m i ly

l e a f a r e a

T o t a l

s u b p l o t

l e a f a r e a

H o s t

s p e c i e s

m ean h e i g h t

F a m i l y

m ean

h e i g h t

T o ta l

m ean

h e i g h t

No. f a m i l y

l e a v e s

T o t a l n o .

o f l e a v e s

P I a n t

d i v e r s i t y

H o s t s p e c i e s

l e a f a r e a

H o s t F a m i1 y

l e a f a r e a

0 . 5 8 8 3

i l l

( 0 . 5 8 7 0 )

I I I

T o t a l s u b p lo t

l e a f a r e a

0 . 3 4 5 8

1

( 0 . 1 0 3 8 )

- 0 . 1 4 7 6

H o s t s p e c i e s

~ ° a n h e i g h t

0 . 3 9 8 8

1

( 0 . 8 4 9 1 )

0 . 8 4 8 3

( 0 . 8 5 1 3 )

0 . 0 0 8 9

( - 0 . 0 1 0 3 )

H o s t F a m i l y

m ean h e i g h t

0 . 3 0 5 8

1

( 0 . 8 5 6 1 )

1

0 . 4 8 7 8 0 .0 3 6 1 0 . 0 8 9 9

( 0 . 1 0 3 1 )

T o ta l m ean

h e i g h t

0 . 3 8 4 3

1

( 0 . 0 8 0 5 )

0 . 1 8 6 8

i l l

-0 . 8 0 1 6 0 .0 0 3 1

( 0 . 0 1 9 7 )

0 .1 1 8 1

No. f a m i l y

l e a v e s

0 . 8 7 8 8

H I

( 0 . 5 9 7 7 )

H I

0 . 8 7 8 8

I I I

-0 . 8531 0 . 1 0 0 9

( 0 . 1 3 1 0 )

0. 8 9 8 9 0 . 0 9 1 0

T o ta l no.

o f l e a v e s

0. 4 3 5 0

I I

I I ( 0 . 4 8 9 6 )

0 . 6 4 0 7

I I I

- 0 . 0 5 1 7 0 . 1 8 1 3

( 0 . 0 1 3 9 )

0 . 1 3 4 ? - 0 . 1 5 0 8 0 . 8 8 5 0

P I a n t

d i v e r s i t y

0 . 3 7 8 6

l

( 0 . 1 0 9 1 )

- 0 . 0 6 7 4 - 0 . 0 9 8 9 0 . 0 8 4 7

( 0 . 0 9 3 1 )

0. 049 1 0. 3 3 8 4

1

- 0 . 0 8 5 4 - 0 . 0 7 3 9

Table 53*1

H o s t

s p e c i e s

l e a f a r e a

H o s t

F a m i l y

l e a f a r e a

T o t a l

s u b p l o t

l e a f a r e a

H o s t

s p e c i e s

m ean h e i g h t

F a s i 1 y

mean

h e i g h t

T o ta l

m ean

h e i g h t

!io. f a m i l y

i e a v e s

T o t a l no.

o f l e a v e s

F I a n t

d i v e r s i t y

H a s t s p e c i e s

l e a f a r e a

H o s t F a m i l y

l e a f a r e a

0 . 7 8 5 3

i l l

T o t a l s u b p l o t

l e a f a r e a

0 . 5 9 4 9

I I I

0 . 6 3 8 8

I I I

H o s t s p e c i e s

m ean h e i g h t

0 .1 1 8 1 0 . 1 7 3 4 0. 0 7 8 3

H o s t F a m i l y

m ean h e i g h t

0 . 0 0 6 8 0 . 8 1 6 0 0 . 1 9 5 8 0 . 4 8 8 5

1

T o t a l m ean

h e i g h t

- 0 . 1 4 1 8 0 . 0 0 8 8 -0 . 8 0 1 6 0 . 1 9 5 7 0 . 6 0 0 0

I I I

No. f a m i l y

l e a v e s

0. 8 6 8 3 0 . 4 1 3 9

l

0. 087 1 - 0 . 0 0 4 0 0 . 1 1 0 5 - 0 . 1 0 8 0

T o t a l no.

o f l e a v e s

- 0 . 8 0 0 1 - 0 . 8 8 8 4 - 0 . 0 5 1 7 - 0 . 1 7 4 7 - 0 . 0 7 8 3 - 0 . 1 5 0 8 9 .1 8 0 1

P l a n t

d i v e r s i t y

- 0 . 3 6 9 6

1

- 0 . 1 6 7 0 - 0 . 0 9 8 9 - 0 . 0 5 5 3 0 . 1 3 4 1 0 . 3 3 8 4 -0 . 8 8 5 6 - 0 . 0 7 3 9

Table 5,3h

163

H o s t

s p e c i e s

l e a f a r e a

H o s t

F a m i1 y

l e a f a r e a

T o ta l

s u b p l o t

l e a f a r e a

H o s t

s p e c i e s

m ean h e i g h

Fam i 1 y

mean

h e i g h t

T o ta l

mean

h e i g h t

Ho. f a m i l y

l e a v e s

T o ta l no.

o r l e a v e s

P l a n t

d i v e r s i t y

H o s t s p e c i e s

l e a f a r e a

H o s t F a m i l y

l e a f a r e a

Q. 5 7 7 9

I I I

( 0 . 2 6 2 3 )

T o ta l s u b p lo t

l e a f a r e a

0 . 5 7 5 3

I I I

( 0 . 2 1 2 8 )

0 . 8 6 0 0

I I I

H o s t s p e c i e s

mean h e i g h t

0 . 3 3 4 1

l

( 0 . 6 5 4 3 )

i l l

0 . 0 3 7 3

( 0 . 0 7 7 3 )

0 . 0 2 5 8

( - 0 . 0 5 1 4 )

H o s t F a m i l y

mean h e i g h t

- 0 . 3 1 9 6

1

( 0 . 5 3 7 0 )

I I I

- 0 . 1 1 6 5 - 0 . 2 4 9 9

( - 0 . 2 4 9 9 )

0 . 2 2 2 6

( - 0 . 2 4 9 9 )

T o t a l m ean

h e i g h t

- 0 . 1 9 5 3

( 0 . 5 2 8 6 )

I I I

- 0 . 0 0 3 4 -0 . 0 9 4 4

( - 0 . 0 9 4 4 )

0 . 2 7 0 3

( 0 . 1 7 0 7 )

H 0 . 8 5 2 8

1

No. f a m i l y

l e a v e s

I I 0 . 6 8 6 8

( - 0 . 0 9 3 9 )

• 0 . 5 4 9 5

I I

0. 4991

I I I

(0 . 4 9 9 1 )

0 . 3 3 1 7

( - 0 . 2 0 2 5 )

- 0 . 0 9 9 1 - 0 . 0 0 3 5

T o ta l no.

o f l e a v e s

I I 0 . 4 8 6 1

( - 0 . 1 9 9 5 )

0 . 3 2 8 1

l

0. 4791

i l l

0 . 2 9 9 6

I I

( - 0 . 2 8 9 8 )

- 0 . 2 4 8 6 - 0 . 1 0 5 6 0 . 5 5 2 8

I I I

P I a n t

d i v e r s i t y

0 . 1 1 5 0

( - 0 . 0 8 3 7 )

- 0 1 7 7 0 - 0 . 208 1 0 . 3 1 3 8

1

( - 0 . 1 8 1 2 )

- 0 . 0 4 9 2 - 0 . 1 3 6 1 0 . 0 6 3 7 - 0 . 0 7 7 2

H o s t

s p e c i e s

l e a f a r e a

H o s t

F a m i l y

l e a f a r e a

T o ta l

s u b p l o t

l e a f a r e a

H o s t

s p e c i e s

m ean h e i g h t

Fam i 1 y

m ean

h e i g h t

T o ta l

mean

h e i g h t

No. f a m i l y

1 e a v e s

T o ta l no.

o f l e a v e s

P I a n t

d i v e r s i t y

H o s t s p e c i e s

l e a f a r e a

H o s t F a m i l y

l e a f a r e a

T o t a l s u b p l o t

l e a f a r e a

0. 4 7 2 0

I I I

H o s t s p e c i e s

m ean h e i g h t

0 . 3 9 7 3

I I

0. 258 1

H o s t F a m i l y

m ean h e i g h t

T o t a l m ean

h e i g h t

- 0 . 0 3 8 2 -0 . 0 9 4 4 0. 2 9 2 6

No. fa m i 1 y

l e a v e s

0 . 8 7 0 1

I I I

0. 2 7 2 6 0. 3 0 5 9

i

- 0 . 1481

T o t a l no.

o f l e a v e s

0 . 3 6 3 8

l

0 . 4 7 9 1

I I I

0 . 4 2 2 7

I I

- 0 . 1 0 5 6

P l a n t

d i v e r s i t y

0 . 1 1 1 7 - 0 . 208 1 0 . 3 1 8 8 -0 . 1361 - 0 . 0 7 7 2

Table 5.3L

164

Fig 5. Host plant family and adult abundance of abundantherbivore species recorded on the four younger serai stages. Data pooled over two years. (a) Apion apricans = 8.93, P < 0.01; (b) Apion assimile,F^s ^ = 9.571, P < 0.01; (c) Apion aethiops, F^= 21.52, P < 0.001; (d) Sitona lineatus. (3,14)= 2.315,4.459, P < 0.05; (e) Sitona hispiduius, F P > 0.05; (f) Sitona sulcifrons, F

(g) Macrosteles laevis, F ^' = 4.43, P > 0.05;

0.05; (3,3)(4,5)= 0.236, P >

= 62.35, P <0.001; (h) Recilia coronifera, F(i) Adarrus ocellaris, F(3,13)

(3,7)= 11 .829, P < 0.01; (j)Psammotettix confinis, F ,0 = 12.19, P < 0.01; (k)---------------------------------- ---------------------Eusceiis incisus, F,(3,13)Mocydiopsis parvicauda, F^

= 41.11, P < = 11.07,

0 .001; (!)

P < 0.01(m) Elymana sulphurella-*, F ^ = 6.06, P < 0.05(n) Zyqinidia scute!iaris, F ^ 12) = 27-86' P < 0.001(o) Javeseila pellucida, F ^ = 8.713, P < 0.01; (p) Dicranotropis hamata, F ^ = 2.904, P > 0.05; (q)Paralabwrnia dalei, F(3,8) = 6 .33, P < 0.05. P <0.05, ** P < 0 .01, *** P < 0.001.

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165

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1 6 8

d i f f e r e n c e ( F i g s 5 . 2 a - c ) . T h e p a t t e r n s o f w e e v i l a b u n d a n c e w ith

s u c c e s s io n w e r e s im i la r to t h o s e o f a b s o lu t e a b u n d a n c e b y h o s t

p la n t f a m i ly , e x c e p t f o r A _ a e t h i o p s , w h e r e a d u l t a b u n d a n c e

v a r i e d as d e s c r i b e d f o r a b s o lu t e a b u n d a n c e b y h o s t p la n t

s p e c i e s . A b s o l u t e a b u n d a n c e b y h o s t p la n t fa m ily o f a ll

C ic a d e l l id a e s p e c ie s in v e s t i g a t e d d i f f e r e d s i g n i f i c a n t l y b e tw e e n

s e r a i s t a g e s , e a c h s p e c i e s s h o w in g a d i f f e r e n t p a t t e r n o f

a b s o lu t e a b u n d a n c e ( F i g s . 5 . 1 g - m ) . A n a l y s i s o f a b s o lu t e

a b u n d a n c e b y h o s t p la n t s p e c i e s , h o w e v e r , r e v e a le d th a t o n l y

t h r e e o f th e s i x C i c a d e l l i d a e s p e c ie s c o n s i d e r e d d i f f e r e d

s i g n i f i c a n t l y b e tw e e n s e r a i s t a g e s ( F ig s 5 . 2 d - i ) . A d u l t

A u c h e n o r r h y n c h a a b u n d a n c e t e n d e d to v a r y b e tw e e n s e r a i s t a g e s

in a s im i la r m a n n e r as a b s o lu t e a b u n d a n c e . O f th e t h r e e s p e c ie s

o f D e lp h a c id a e , o n ly h a m a ta s h o w e d no d i f f e r e n c e b e tw e e n

s e r a i s t a g e s f o r e i t h e r m e a s u r e o f a b s o lu t e a b u n d a n c e ( F i g s .

5 . 1 o - q , 5 . 2 j—k ) .

5 . 3 . i i i V a r i a t i o n in o v e r w i n t e r i n g s t r a t e g ie s a n d s p e c ie s

r i c h n e s s

T h e a n a l y s i s o f a b s o lu t e a b u n d a n c e o f C i c a d e l l id a e o v e r w i n t e r i n g

as e g g s a n d a d u l t s r e v e a le d n o s i g n i f i c a n t d i f f e r e n c e b e tw e e n

th e s e s t r a t e g i e s ( F i g . 5 .3 ) ( F ^ = 0 .0 1 2 3 , P > 0 . 0 5 ) .

T h e s p e c ie s r i c h n e s s o f H e t e r o p t e r a w as s i g n i f i c a n t l y p o s i t i v e l y

c o r r e la t e d w ith t h a t o f C u r c u i i o n o i d e a a n d C i c a d e l l id a e on th e

r u d e r a l s i t e a n d th a t o f C i c a d e l l i d a e w ith C u r c u i i o n o i d e a . No

s i g n i f i c a n t r e la t io n s w e re o b s e r v e d in e a r l y o r e a r l y

m i d s u c c e s s i o n , h o w e v e r in la te s u c c e s s io n t h e s p e c i e s r i c h n e s s o f

C ic a d e l l id a e w as s i g n i f i c a n t l y p o s i t i v e l y c o r r e la t e d w ith t h a t o f

H e t e r o p t e r a a n d D e lp h a c id a e ( T a b l e 5 .4 )

5 . 3 . iv V a r i a t i o n in a b s o l u t e a b u n d a n c e o f b i r c h h e r b i v o r e s

a s s o c ia t e d w ith th e u p p e r a n d lo w e r c a n o p y

T h e r e w e r e n o s i g n i f i c a n t d i f f e r e n c e s in th e a b s o lu t e a b u n d a n c e

o f in s e c t g r o u p s o c c u r r i n g o n t h e u p p e r a n d lo w e r c a n o p y ( F ig

5 . 4 a - e ) . H o w e v e r , w ith t h e e x c e p t i o n o f th e P s y l l i d a e , t h e r e

w as a s i g n i f i c a n t d a t e e f f e c t f o r all g r o u p s ( F i g s . 5 . 5 a - e ) .

G e n e r a l l y , a b s o lu t e a b u n d a n c e w a s h i g h e a r l y in t h e y e a r , fe l l in

Fig 5. M ean a b s o l u t e a b u n d a n c e b y h o s t p la n t s p e c ie s o f

a b u n d a n t h e r b i v o r e s p e c ie s r e c o r d e d on th e f o u r

y o u n g e r s e r a i s t a g e s . Data p o o le d o v e r tw o y e a r s ,

(a) A p i o n a s s i m i l e , gj = 1 1 .9 1 , P < 0 . 0 1 ; (b )

A p i o n a p r i c a n s , F ^ ^ = 1 1 .4 8 , P < 0 .0 0 1 ; ( c ) A p i o n

a e t h i o p s , F ^ = 8 .9 7 , P > 0 . 0 5 ; (d ) P s a m m o te tt ix

c o n f i n i s , F( 2 , 2 )

= 5 .0 4 ,

s u l p h u r e l l a , F ^ ^ = 0 .7 9 ,

l a e v i s , F ^ = 1 8 .3 6 ,

c o r o n i f e r a , F ^ ^ = 7 .9 5 ,

o c e i l a r i s , frr> = 1 0 .0 5 ,

P > 0 .0 5 ; (e) E ly m a n a

P > 0 .0 5 ; ( f l M a c r o s te le s

P

( 3 ,2 7 )s c u t e l l a r i s , F ^ ^

D i c r a n o t r o p i s h a m a ta , F ,_ D ,~~~ —— — l O * O JP a r a ia b u r n i a d a le i F , n--------- --- li,oJ

< G.05;

P > 0 .0 5 ;

P < 0.001;

( g } R e d l ia

(h ) A d a r r u s

(i) Z y g i n id ia

2 9 .1 4 , P < 0 .0 0 1 ; (j)

= 2 . 8 4 , P > 0 .0 5 ; (k )

= 1 4 .5 2 3 , P < 0 . 0 1 . * P <

0 . 0 5 , ** P < 0 .0 1 , *** P < 0 .0 0 1 .

1 6 9

FIG 5.2

8

3

18000 17000 - 16000 - 15000 - 14000 - 13000 - 12000 - 11000 - 10000 - 9000 - *000 - 7000 - 6000 - 5000 - 4000 - 3000 - 2000 - 1000 -

a)APION ASSIMUJE ***

a

E EMSSERAL STAGE

b)APION AP RICANS

8

3§

8

SERALSTAGE

c)APION AETHIOPS

&IS

8

■ ABSOLUTE ABUNDANCE

O ADULT ABUNDANCE

1 7 0

FIG 5.2d)P S A M M onrrnx c o n f in is e)ELYMANA SULPHURELLA

g)RECILIA CORONIFERA

£1£a0

hYADARRUS OCELLARIS

SERAL STAGE

no

a0

m ABSOLUTE ABUNDANCE

O ADULTABUNDANCE

171

FIG 5.2

B

-1OCO3

150j)DICRANOTROPIS HAMATA

200

B EMSSERAL STAGE

k)PARALABHRNIA DALEI **

B

3

(3co9

EMSSERAL STAGE

LMS

ABSOLUTE ABUNDANCE

O ADULT ABUNDANCE

ADULT ABUNDANCE ADULT ABUNDANCE

F ig 5 .3 M e a n a b s o lu t e a b u n d a n c e b y h o s t p la n t fa m i ly o f

C ic a d e l l id a e o v e r w i n t e r i n g as e g g s a n d a d u l t s . D ata

p o o le d o v e r a ll s i t e s a n d tw o y e a r s .

1 7 2

FIG 5.3

OVERWINTERING STAGE

T a b l e 5.4> P e a r s o n 's C o r r e l a t i o n C o e f f i c ie n t f o r s p e c i e s

r i c h n e s s o f H e t e r o p t e r a , C u r c u l i o n o i d e a ,

C ic a d e i l id a e a n d D e lp h a c id a e w ith t h a t o f t h e o t h e r

in s e c t g r o u p s d u r i n g A u g u s t 1985, in r u a e r a l ,

e a r l y , e a r l y m id a n d late m i d s u c c e s s i o n . * P <

0 .0 5 , ** P < 0.01, *** P < 0.001.

173

INSECT GROUP

Serai Stage Insect Group H eteroptera Curculi onoi dea Ci c a d e l1 i dae Del phaci dae

Ruderal Heteroptera - 0.3750*

0. 4125 f t

0. 0962

Curcul i onoi dea - 0. 3470f t

-0. 0037

C icadel1 i dae - 0. 1206

Del phaci dae -

Earl y H eteroptera - -0. 1000 -0 .0225 -0. 2102

Curcul ionoidea - 0.1651 0. 0038

C icad el1 i dae - 0. 1692

Oel phaci dae -

Early Mid Heteroptera - 0. 1531 -0 . 0465 0. 1479

Curcul ionoidea - 0. 1691 0. 0475

C icadel1 i dae - 0.2403

Del phaci dae -

Late Mi d H eteroptera - 0. 1503 0. 3420 *

0. 2695

Curcul i onoi dea - -0. 0422 0. 0053

Cicadel 1 i dae - 0. 3223 *

Delphaci dae -

TABLE 54

Fig 5.4 M ean a b s o lu te a b u n d a n c e o f h e r b i v o r e s on th e

u p p e r a n d low er c a n o p y o f b i r c h in 1985. (a)

C u r c u i i o n o i d e a , ^ = 0 . 5 3 , P > 0 .0 5 ; (b )

C ic a d e l l id a e ( e x c l u d i n g T y p h l o c y b i n a e ) , F ^ ^ =

0 .1 4 1 , P > 0 .0 5 ; (c ) T y p h l o c y b i n a e , F ^ ^ =

0 .6 8 , P > 0 .0 5 ; ( d ) P s y i l i d a e , F (1 ^ = 0 .0 3 5 , P

> 0 .0 5 ; (e) H e t e r o p t e r a , K r u s k a l l - W a l l i s = 0 .0 1 8 ,

n = 1 2 0 2 , P > 0 .0 5 . D a ta p o o le d o v e r a ll d a t e s .

H a t c h e d c o lu m n s = u p p e r c a n o p y , o p e n c o lu m n s =

low er c a n o p y . B a r s r e p r e s e n t s t a n d a r d e r r o r s .

ABSOLUTE ABUNDANCE ABSOLUTE ABUNDANCE

ABSOLUTE ABUNDANCECANOPY

CANOPY

ABSOLUTE ABUNDANCE

oU\

ABSOLUTE ABUNDANCE

174

Fig 5.5 M ean a b s o lu t e a b u n d a n c e on b i r c h d u r i n g e a c h

m o n th in 1985. (a) C u r c u i i o n o i d e a , ^ ) =

2 3 .5 6 , P < 0 . 0 0 1 ; (b) C i c a d e l l id a e ( e x c l u d i n g

T y p h l o c y b i n a e ) , ^ = 3 5 .0 2 , P < 0 .0 1 ; (c)

T y p h i o c y b i n a e , F 3 = 2 6 .4 3 , P < 0 .0 0 1 ; (d)

P s y l l i d a e , F 5 ^ = 1 .9 5 , P > 0 .0 5 ; (e)

H e t e r o p t e r a , low er c a n o p y , K r u s k a l l - W a l i i s =

65.3951 , n = 857, P > 0 .0 0 1 ; u p p e r c a n o p y ,

K r u s k a l l - V V a l l i s = 7 7 .8 6 2 7 , n = 3 4 5 , P < 0 . 0 0 1 .

H a t c h e d c o lu m n s = u p p e r c a n o p y , o p e n c o lu m n s =

lo w e r c a n o p y . B a r s ( a ) - ( d ) r e p r e s e n t s t a n d a r d

e r r o r s . D a ta p oo le d o v e r b o th c a n o p ie s f o r all

g r o u p s e x c e p t H e t e r o p t e r a , as no s i g n i f i c a n t

c a n o p y . d a t e in t e r a c t io n .

AUGUST

o u . o S o & i © £ § o o o o o o S

ABSOLUTE ABUNDANCE ABSOLUTE ABUNDANCE

03

FIG 5.5

176

FIG 5.5

0

S

DATE

ABSOLUTE AB

UNDA

NCE

1 7 7

FIG 5.5

100

90

80

7060

5040

302010

0

e)HETEROPTERA

APRIL n — — t-MAY JUNE JULYDATE

AUG SEPT

I I LO W ER CANOPY U PPER CANOPY

1 7 8

m id s u m m e r a n d in c r e a s e d d u r i n g a u t u m n . A d u l t T y p h l o c y b i n a e

w e re n o t r e c o r d e d u n t i l J u n e , a f t e r w h ic h t h e i r a b s o lu t e

a b u n d a n c e in c r e a s e d u n t i l th e e n d o f th e s e a s o n . C o n s i d e r a t io n

o f s i n g le s p e c ie s s h o w e d th a t o n ly th e h e t e r o p t e r a n , K l e i d o c e r y s

r e s e d a e s h o w e d a d i f f e r e n c e in a b s o lu te a b u n d a n c e b e tw e e n

u p p e r a n d low er c a n o p ie s , b e in g s i g n i f i c a n t l y g r e a t e r in th e

lo w e r c a n o p y .

5 .4 D I S C U S S I O N

In v ie w o f th e h ig h d e g r e e o f a u t o c o r r e la t io n b e tw e e n m e a s u r e d

h o s t p la n t a n d c o m m u n ity a t t r i b u t e s , c o n c lu s io n s a b o u t th e

im p o r t a n c e o f a n y s i n g le a t t r i b u t e on th e a b u n d a n c e o f a s p e c i e s

m u s t b e m ade w ith c a u t io n . H o w e v e r , c e r t a in o v e r - r i d i n g a n d

c o n s i s t e n t p a t t e r n s w e r e a p p a r e n t . W eev il a b u n d a n c e w as

s t r o n g l y c o r r e la t e d w ith m o s t c o m m u n ity a t t r i b u t e s on th e

y o u n g e r s u c c e s s io n a l s i t e s , w h e r e a s th e a b u n d a n c e o f

A u c h e n o r r h y n c h a d i s p l a y e d f a r lo w er d e g r e s s o f c o r r e l a t i o n .

T h i s d ic h o t o m y m ay o c c u r f o r tw o r e a s o n s : f i r s t l y , d i f f e r e n c e s

in m ode o f fe e d in g o r s e c o n d l y , d i f f e r e n c e s in h o s t p la n t

s p e c i f i c i t y . T h e w e e v i l s p e c i e s c o n s id e r e d a r e h i g h l y h o s t

s p e c i f i c a n d on th e y o u n g e r s i t e s t h e i r h o s t p l a n t s , s p e c i e s o f

L e g u m i n o s a e , a r e im p o r t a n t d e t e r m in a n t s o f c o m m u n ity s t r u c t u r e

(s e e s e c t io n 3 . 3 ) . If w e e v i l a b u n d a n c e is d e t e r m in e d b y a n y o n e

h o s t p la n t a t t r i b u t e , th e n b y v i r t u e o f th e o b s e r v e d

a u t o c o r r e l a t io n it w o u ld b e r e la t e d to o t h e r a t t r i b u t e s . O n th e

r u d e r a l a n d e a r ly s u c c e s s io n s i t e s , w e e v i l a b u n d a n c e w as

c o r r e l a t e d w ith b o th h o s t p la n t a n d c o m m u n ity a t t r i b u t e s ,

w h e r e a s in e a r ly m id s u c c e s s io n w h e r e L e g u m in o s a e a r e n o t

im p o r t a n t c o m p o n e n ts o f c o m m u n it y s t r u c t u r e (see s e c t io n 3 . 3 ) ,

a b u n d a n c e w as o n ly c o r r e l a t e d w ith h o s t p la n t a t t r i b u t e s . T h i s

s u g g e s t s t h a t g e n e r a l c o m m u n it y a t t r i b u t e s m ay n o t be im p o r t a n t

d e t e r m in a n t s o f w e e v i l a b u n d a n c e . It a p p e a r s t h a t sm all s c a le

v a r ia t i o n in w e e v il a b u n d a n c e is a f f e c t e d m ore b y c e r t a i n

f e a t u r e s o f th e h o s t p la n t . L e a f a re a a n d th e s t r u c t u r e o f th e

h o s t p la n t a r e l i k e ly to be im p o r t a n t , b u t i t is im p o s s ib le to

s e p a r a t e th e r e la t iv e im p o r ta n c e o f th e s e a t t r i b u t e s w ith t h e s e

d a t a .

179

O n th e o t h e r h a n d , th e A u c h e n o r r h y n c h a s h o w e d l i t t le

c o r r e la t i o n w ith a n y m e a s u r e d h o s t p la n t o r c o m m u n ity a t t r i b u t e .

T h i s c o u ld be d u e to i n c o r r e c t h o s t p la n t id e n t i f i c a t io n fro m th e

l i t e r a t u r e r e c o r d s , o r th a t as g r a s s - f e e d e r s t h e i r a b u n d a n c e is

d e t e r m in e d m ore b y food q u a l i t y th a n q u a n t i t y . Some e le m e n t o f

c o m m u n ity s t r u c t u r e h a s b e e n in d ic a t e d as im p o r t a n t to c e r t a in

s p e c i e s on m ost s i t e s , a n d le a f a re a is p o s i t i v e l y c o r r e la t e d w ith

a b u n d a n c e o f A d a r r u s o c e l l a r i s , D i c r a n o t r o p i s ham ata a n d

S t e n o c r a n u s m in u t u s on o l d e r s i t e s . G e n e r a l l y th e a b u n d a n c e o f

th e H e t e r o p t e r a w as s t r o n g l y c o r r e la t e d w ith h o s t p la n t le a f a r e a

a n d s t r u c t u r e . H o w e v e r , th e a b u n d a n c e o f th e g e n e r a l i s t

g r a s s - f e e d e r , S te n o d e m a l a e v i g a t u m , w as u n r e l a t e d to a n y

m e a s u r e d c o m m u n ity a t t r i b u t e . O n l y f o r th e C h r y s o m e l i d C a s s i d a

v i t t a t a is it p o s s ib le to s t a t e u n e q u i v o c a l l y th a t h o s t p la n t

s t r u c t u r e is o f p r i m a r y im p o r ta n c e a n d h o s t p la n t a re a o f less

im p o r t a n c e .

In c o n t r a s t to o t h e r s t u d ie s ( B r o w n & S o u t h w o o d , 1983; L a w t o n ,

1978; M o r r i s , 1971, 1979, 1981.; M u r d o c h e t a l , 1972; S o u t h w o o d ,

B r o w n S R e a d e r , 1 9 7 9 ) , no r e l a t i o n s h i p b e tw e e n s p e c ie s r i c h n e s s

a n d a n y m e a s u r e d c o m m u n it y a t t r i b u t e w a s a p p a r e n t . S u c h a

r e s u l t is t h e r e f o r e s u r p r i s i n g ( h o w e v e r , s e e S e d l a c e k , B a r r e t t &

S h a w , 1988). It c o u ld b e t h a t t h e s c a le o f th e s a m p l in g w a s too

sm all to r e f l e c t v a r ia t i o n in s p e c i e s r i c h n e s s , a s u g g e s t io n w h ic h

c o u ld o n ly b e u p h e ld b y s im i la r s t u d ie s e m p lo y in g d i f f e r e n t

s a m p l in g s c a le s ( e . g . M u r d o c h e t a [ , 1 9 7 2 ).

In c o n c l u s i o n , s m a l l - s c a le v a r i a t i o n in c o m m u n ity a t t r i b u t e s m ay

b e im p o r ta n t to h e r b i v o r o u s i n s e c t s , a l t h o u g h d i f f e r e n t a s p e c t s

o f th e c o m m u n ity a r e p r o b a b l y im p o r t a n t to d i f f e r e n t in s e c t

g r o u p s . P la n t s t r u c t u r e , a s m e a s u r e d h e r e , a p p e a r e d to b e o f

som e im p o r t a n c e , e s p e c i a l l y to A u c h e n o r r h y n c h a a n d v i t t a t a .

H o w e v e r , th e r e l a t iv e im p o r t a n t o f s p e c i f i c a s p e c t s o f v e g e t a t io n

s t r u c t u r e a n d th e e c o lo g ic a l r e a s o n s f o r t h e i r im p o r ta n c e w ill

p r o b a b l y o n ly b e id e n t i f i e d b y m a n ip u la t iv e e x p e r i m e n t s . T h e s e

r e s u l t s a lso u n d e r l i n e th e im p o r t a n c e o f th e a p p r o p r i a t e s c a le o f

s t u d y in e c o lo g ic a l r e s e a r c h .

180

T h e m a jo r i ty o f s p e c i e s s h o w e d s i g n i f i c a n t d i f f e r e n c e s in a b s o lu te

a b u n d a n c e b e tw e e n s e r a i s t a g e s w h e n re la t e d to h o s t p la n t

fa m i ly . H o w e v e r , a n a l y s i s o f a b s o lu t e a b u n d a n c e b y h o s t p la n t

s p e c ie s r e v e a le d s i g n i f i c a n t d i f f e r e n c e s fo r o n ly h a l f th e

A u c h e n o r r h y n c h a s p e c i e s a n d tw o o f th e t h r e e w e e v i l s p e c i e s .

T h e la t t e r is p r o b a b l y th e m ost r e l e v a n t m e a s u r e m e n t o f

a b u n d a n c e in t h is a n a l y s i s , a s g e n e r a l i s t in s e c t s p e c ie s m ay well

s w it c h h o s ts in d i f f e r e n t s e r a i s t a g e s , a n d t h e r e b y a f f e c t th e

r e s u l t s . No s i n g le f a c t o r a p p e a r s to d e te r m in e w h ic h s p e c ie s

d i f f e r in a b s o lu t e a b u n d a n c e b e tw e e n s e r a i s t a g e s . It is

i n t e r e s t i n g th a t s p e c i e s s h a r i n g a h o s t p la n t o f te n d i f f e r in t h e i r

p a t t e r n o f a b s o lu t e a b u n d a n c e b e tw e e n s e r a i s t a g e s . T h i s

s u g g e s t s th a t a h o s t p la n t s p e c i e s is n o t n e c e s s a r i l y a u n i fo r m

r e s o u r c e f o r a ll h e r b i v o r e s p e c i e s . C e r t a in p la n t a t t r i b u t e s m ay

v a r y b e tw e e n s e r a i s t a g e s to a g r e a t e r e x t e n t th a n o t h e r s , a n d

th e d i f f e r e n t i a l im p o r ta n c e o f c e r t a in a t t r ib u t e s b e tw e e n s e r a i

s t a g e s m ay e x p l a i n , a t le a s t in p a r t , th e d i f f e r e n c e in a b u n d a n c e

o f s p e c i e s s h a r i n g th e sam e h o s t p la n t .

It w a s n o t e x p e c t e d t h a t a b s o lu t e a b u n d a n c e o f b i r c h h e r b i v o r e s

w o u ld d i f f e r b e tw e e n th e u p p e r a n d lo w e r c a n o p y , s in c e a n y

d i f f e r e n c e s in th e d e f e n s i v e c h e m i s t r y o f b i r c h r e la t e d to fo l ia g e

h e i g h t a r e u n l i k e l y . O f t h e i n d i v i d u a l s p e c ie s s t u d i e s , o n l y

K l e i d o c e r y s r e s e d a e s h o w e d a s i g n i f i c a n t d i f f e r e n c e in a b s o lu t e

a b u n d a n c e b e tw e e n c a n o p i e s , a n d t h is p r o b a b l y r e f le c t s i t s

p r e f e r e n c e f o r c a t k i n s ( S o u t h w o o d S L e s t o n , 1959) w h ic h w e r e

m ore a b u n d a n t in th e lo w e r c a n o p y . S e a s o n a l c h a n g e s in

a b s o lu t e a b u n d a n c e a g r e e w ith k n o w n c h a n g e s in b i r c h c h e m i s t r y

(se e C h a p t e r 6 ) . T h e r e s u l t s f o r th e P s y l l id a e a r e d i f f i c u l t to

e x p l a i n , a n d m ay be c o m p l ic a t e d b y t h e i r low a b u n d a n c e .

T h e m o s t i n t e r e s t ^ p o i n t to e m e r g e fro m th e c o r r e la t i o n a n a ly s i s

o f in s e c t g r o u p s p e c i e s r i c h n e s s w as th e g e n e r a l la c k o f a

s i g n i f i c a n t r e l a t io n s h ip b e tw e e n C ic a d e l l id a e a n d D e lp h a c id a e

s p e c ie s r i c h n e s s ' . A s b o th g r o u p s a r e e c o lo g ic a l ly s im i la r a n d

s h a r e h o s t p l a n t s , a s i g n i f i c a n t r e l a t io n s h ip m ay b e e x p e c t e d , i t s

fo rm d e p e n d in g on th e im p o r t a n c e o f d i f f e r e n t s t r u c t u r i n g

f o r c e s , i . e . c o m p e t i t io n , o r c o m b in e d u s e o f g o o d q u a l i t y

r e s o u r c e . T h e a n a l y s i s o f C i c a d e l l id a e o v e r w i n t e r i n g as e g g s

1 8 1

a n d a d u l t s r e v e a le d no d i f f e r e n c e in a b s o lu t e a b u n d a n c e , a n d

t h e r e f o r e s h e d s no l i g h t on th e d i f f e r e n t p a t t e r n s o f C i c a d e l l id a e

a n d D e lp h a c id a e a b s o lu t e a b u n d a n c e , w h ic h r e m a in s u n e x p l a i n e d .

T h e s e r e s u l t s s u g g e s t th a t d e s p i t e m an y s im i la r i t ie s th e s e two

g r o u p s a r e e c o lo g ic a l ly v e r y d i f f e r e n t .

T h i s c h a p t e r a im ed to e x p l a i n th e v a r ia t io n in th e r e l a t iv e a n d

a b s o lu t e a b u n d a n c e o f s i n g l e h e r b i v o r e s p e c i e s to s m a l l - s c a le

c o m m u n ity d i f f e r e n c e s . S u c h a n a ly s e s o f s i n g le s p e c ie s a r e

n e c e s s a r y b u t th e i n t e r p r e t a t i o n o f r e s u l t s r e q u i r e an i n - d e p t h

k n o w le d g e o f th e n a t u r a l h i s t o r y o f th e s p e c i e s . P e r h a p s w h a t

is n e e d e d to p r o v i d e a f u l l e r u n d e r s t a n d i n g o f th e v a r ia t i o n in

i n d i v i d u a l s p e c i e s r e s p o n s e a n d r e la t io n s to v e g e t a t io n a t t r i b u t e s

is " to d o m ore e le g a n t a n d s o p h i s t i c a t e d n a t u r a l h i s t o r y . It is

in n a t u r e th a t b o th th e q u e s t i o n s a n d a n s w e r s lie" ( D i n g l e ,

1983).

1 8 2

C H A P T E R S I X

V A R I A T I O N IN F O O D Q U A L I T Y A N D P E R F O R M A N C E O F

E R A N N I S D E F O L 1 A R 1 A ( L E P 1 D O P T E R A : C E O M E T R 1 D A E )

6 . 1 I N T R O D U C T I O N

It is a v i t a l c o m p o n e n t o f L a w to n S M c N e i l l ' s t h e o r y (1979) t h a t

th e i n t r i n s i c ra te o f in c r e a s e ( r ) o f a h e r b i v o r e p o p u la t io n is

r e d u c e d w h e n f e e d in g on a d i e t c o n t a in in g q u a n t i t a t iv e d e f e n c e s

( s e n s u F e e n y ) . In o r d e r f o r th e i n t r i n s i c ra t e o f in c r e a s e to be

r e d u c e d , i n d i v i d u a l h e r b i v o r e s m u s t h a v e in c r e a s e d g e n e r a t io n

t im e s , g r e a t e r m o r t a l i t y , r e d u c e d f e c u n d i t y , o r a n y c o m b in a t io n

o f t h e s e t h r e e p a r a m e t e r s . T h i s c h a p t e r a im s to in v e s t ig a t e

w h e t h e r a n y o f th e s e p a r a m e t e r s a r e a f f e c t e d b y q u a n t i t a t i v e

d e f e n c e s in a com mon h e r b i v o r e o f b i r c h .

Q u a n t i t a t i v e d e f e n c e s a r e g e n e r a l l y a s s o c ia te d w ith a p p a r e n t

p la n t s e . g . t r e e s ( F e e n y , 1 9 7 6 ) . T h e le a v e s o f t r e e s u n d e r g o

c o n s i d e r a b l e ch e m ic a l c h a n g e s d u r i n g t h e i r l i fe t im e . T y p i c a l l y ,

y o u n g le a v e s a r e le ss to u g h t h a n o ld e r le a v e s a n d h a v e h i g h e r

w a t e r a n d n i t r o g e n c o n t e n t s . T h e p h e n o l ic c o n t e n t o f le a v e s

t e n d s to in c r e a s e w ith le a f a g e a n d th e n i t r o g e n a n d w a t e r

c o n t e n t d e c r e a s e s ( F e e n y , 1970; H a u k io j a , N ie m e la , I s o - l i v a r i ,

O ja la & A r o , 1978; A y r e s & M a sC le a n , 1987; S c r i b e r , 1977; F a e t h ,

M o p p e r & S i m b e r lo f f , 1981).

P h e n o l ic c o m p o u n d s , e . g . t a n n i n s a n d r e s in s a lo n e do n o t

c o n s t i t u t e a q u a n t i t a t iv e d e f e n c e . F e e n y (1976) s ta te s " t h e

p r o p e r t i e s o f d e c r e a s i n g n i t r o g e n a n d w a te r c o n t e n t , c o m b in e d

w ith t o u g h le a v e s a n d th e p r e s e n c e o f t a n n in s a ll c o n f e r u p o n

o a k le a v e s a 'q u a n t i t a t iv e ' d e f e n c e a g a i n s t h e r b i v o r e s a n d

p a t h o g e n s " . M a n y w o r k e r s h a v e in v e s t ig a t e d th e e f f e c t s o f

q u a n t i t a t i v e d e f e n c e s o n h e r b i v o r e p e r f o r m a n c e . It h a s b e e n

s u g g e s t e d th a t le a f t o u g h n e s s is im p o r t a n t to h e r b i v o r e s . F e e n y

(1970) a n d K r a f t & D e n n o (1982) s u g g e s t th a t th e s e a s o n a l

i n c r e a s e in le a f t o u g h n e s s is t h e m ain r e a s o n w h y m a n y la r v a e

fe e d o n y o u n g f o l ia g e . S c r i b e r (1977) s h o w e d th a t L e p i d o p t e r a

l a r v a e fe d le a v e s low in w a t e r g r e w m o re s lo w ly th a n la r v a e fe d

183

le a v e s f u l l y s u p p le m e n t e d w ith w a t e r . M i le s , A s p i n a l l & C o r n e l l

(1 9 8 2 ) , h o w e v e r , r e p o r t th e p e r f o r m a n c e o f P a r o p s is a to m a r ia

( C o le o p t e r a : C h r y s o m e l id a e ) to be s im i la r on h o s t p la n t s

s u b j e c t to d i f f e r e n t w a te r r e g im e s . T h e m a jo r i t y o f w o rk h a s ,

h o w e v e r , b e e n c o n d u c t e d on th e e f f e c t s o f t a n n in a n d n i t r o g e n

on h e r b i v o r e p e r f o r m a n c e . T h e in t e r a c t io n s o f b o th ta n n in s a n d

p la n t n u t r i e n t s w ith h e r b i v o r e s h a s b e e n r e v ie w e d in th e g e n e r a l

i n t r o d u c t i o n ( s e c t io n s 1 .3 & 1 . 4 ) .

S e v e r a l w o r k e r s h a v e ta k e n an h o l i s t ic a p p r o a c h a n d h a v e

in v e s t ig a t e d th e e f f e c t o f a l l th e c o n s t i t u e n t s o f q u a n t i t a t iv e

d e f e n c e s on h e r b i v o r e p e r f o r m a n c e . T h e s e s t u d ie s te n d to

u t i l i s e th e s e a s o n a l c h a n g e s w h ic h o c c u r in le a v e s as n a t u r a l

m a n ip u la t io n s o f q u a n t i t a t iv e d e f e n c e s . F e e n y (1970) fo u n d t h a t

0 . b ru m a ta fe d on y o u n g o a k le a v e s h a d i n c r e a s e d s u r v i v a l a n d

g r e a t e r p u p a l w e ig h t s th a n la r v a e fe d o ld e r o a k le a v e s . In a

s t u d y o f f i f t e e n s p e c ie s in t h e t r ib e L i t h o p h a n in i ( L e p i d o p t e r a :

N o c t u id a e ) S c h w e i t z e r (1979) fo u n d t h a t t w e lv e s p e c ie s h a d

g r e a t e r la r v a l w e ig h t s on a d i e t o f y o u n g fo l ia g e th a n th o s e o n a

d ie t o f o l d e r f o l ia g e . S im i la r r e s u l t s w e r e o b t a in e d b y H o u g h &

Pim en te l (1978) w ith G y p s y M o th ( L y m a n t r i a d i s p a r L .

L e p i d o p t e r a : G e o m e tr id a e ) f e e d in g on o a k ; K r a f t & D e n n o (1982)

w ith T r i r h a b a d a b a c h a r i d i s (W e b e r) ( C o le o p t e r a : C h r y s o m e l id a e )

f e e d in g o n a w o o d y p e r e n n ia l s h r u b , B a c c h a r i s h a l im ifo l ia

( C o m p o s i t a e ) ; A y r e s & M a c ie a n (1987) w ith E p i r r i t a a u t u m n a ta

( B o n k h a u s e n ) ( L e p i d o p t e r a ; L a r e n t i in a e ) o n B e tu la p u b e s c e n s

s s p . t o r t u o s a a n d b y D am m an (1987) w ith O m p h a lo c e r a m u n r o e i

M a r t in ( L e p i d o p t e r a : P y r a l id a e ) fe e d in g o n le a v e s o f th e g e n u s

A s im in a ( A n n o n a c c .e a e ) . T h o m a s (1987) r e p o r t s t h a t le a f a g e is

m ore im p o r t a n t th a n h o s t p la n t s p e c ie s in h o s t p la n t s e le c t io n b y

M o n o m a c ra s p a n d D i s o n y c h a q u in q u e l i n e a t a ( C o le o p t e r a :

C h r y s o m e l id a e ) on P a s s i f lo r a v i n e s . A f ie ld e x p e r im e n t b y

F o w le r & L a w to n (1985) s h o w e d th a t m o s t s p e c i e s o f b i r c h

h e r b i v o r e c o lo n is e d y o u n g b i r c h fo l ia g e in p r e f e r e n c e to o l d e r

fo l ia g e . T h e p r e f e r e n c e f o r y o u n g f o l ia g e is n o t , h o w e v e r ,

u n i v e r s a l . C a t e s (1980) r e p o r t s th a t la r v a e o f m o n o p h a g o u s a n d

o l ig o p h a g o u s i n s e c t h e r b i v o r e s p r e f e r r e d y o u n g le a v e s , w h i le

p o l y p h a g o u s s p e c i e s p r e f e r r e d m a tu r e le a v e s o f t h e i r v a r i o u s

h o s t p l a n t s .

1 8 4

It c a n be se e n t h a t , d e s p i t e m u ch w o r k , th e u n d e r l y i n g t r e n d s

in th e r e l a t io n s h ip b e tw e e n in s e c t h e r b i v o r e s a n d t h e i r h o s t

p la n t s a r e n o t c l e a r . T h e r e is am p le e v id e n c e o f h e r b i v o r e s

p e r f o r m in g b e t t e r o n y o u n g le a v e s th a n on o ld e r o n e s , a l t h o u g h

e x p e r im e n t s s e e k in g to in v e s t ig a t e th e e f f e c t s o f s in g le

p a r a m e t e r s o f food q u a l i t y h a v e b e e n less r e v e a l in g a n d o f te n

c o n t r a d i c t o r y . T h e r e seem s to be l i t t le e v id e n c e s u p p o r t i n g th e

idea o f q u a n t i t a t iv e d e f e n c e s a c t in g in a d o s a g e d e p e n d e n t

m a n n e r as p o s t u la t e d b y F e e n y (1 97 6 ) . T h e ro le o f p h e n o l ic

c o m p o u n d s is p a r t i c u l a r l y u n c l e a r . T h e o n ly s t u d i e s w h ic h

d e m o n s t r a t e c o n c l u s i v e l y an e f f e c t o f q u a n t i t a t i v e d e f e n c e s on

th e p o p u la t io n d y n a m i c s o f h e r b i v o r e s a r e th e w o r k on a p h i d s

( D i x o n , 1963, 1966, 1969, 19 7 5 ). T h i s s y s te m is p e c u l i a r ,

h o w e v e r , as th e h e r b i v o r e is l in k e d so c l o s e ly to th e n i t r o g e n

le v e ls o f th e h o s t p l a n t .

6 . 2 E x p e r i m e n t 1

T H E E F F E C T O F L E A F A G E O N T H E P E R F O R M A N C E

O F E R A N N I S D E F O L I A R I A

6 . 2 . i A im s

T h e a im s o f t h i s e x p e r im e n t a r e to i n v e s t ig a t e w h e t h e r

q u a n t i t a t iv e d e f e n c e s r e d u c e i n d i v i d u a l p e r f o r m a n c e a n d ca n

a f f e c t h e r b i v o r e p o p u la t io n d y n a m ic s .

6 . 2 . i i M a te r ia ls a n d M e th o d s

6 . 2 . i i . a T h e o r g a n is m s

E r a n n i s d e f o l ia r ia C l e r c k ( L e p id o t e r a : G e o m e tr id a e ) ( M o t t le d

U m b e r ) is a com m on m oth in G r e a t B r i t a i n . It is p o l y p h a g o u s ,

r e p o r t e d from B e t u l a , C o r y l u s , C r a t a e g u s , Q u e r c u s , L o n i c e r a ,

R o s a , ( S o u t h , 1908) a n d A c e r ( S . W a r r in g t o n , p e r s . c o m m . ) .

T h e a d u l t m oth f l i e s f ro m O c t o b e r to D e c e m b e r a n d o c c a s io n a l ly

t h r o u g h to M a r c h . T h e w in g le s s fem ales la y e g g s o n th e t w ig s

o f th e h o s t p la n t . T h e la r v a e o c c u r b e tw e e n th e e n d o f M a r c h

a n d J u n e a n d p u p a t e d u r i n g J u n e on o r b e lo w g r o u n d a t th e

b a s e o f th e h o s t t r e e ( S c o r e r , 1913).

1 8 4

B e tu la p e n d u la R o th ( B e t u la c e a e ) ( S i l v e r B i r c h ) is a com m on t r e e

in w o o d s t h r o u g h o u t th e B r i t i s h I s le s , e s p e c ia l ly on l i g h t d r y

s o i ls a n d h e a t h s , b u t it is r a r e in S c o t la n d a n d on c a lc a r e o u s

s o i l s in E n g la n d a n d W ales ( C l a p h a m , T u t i n & W a r b u r g , 19 8 1 ).

6 . 2 . i i . b S a m p l in g a n d e x p e r im e n t a l p r o c e d u r e

M o th s

Fem ale E . d e fo l ia r ia w e r e c a u g h t a t S i lw ood P a r k , B e r k s h i r e a n d

W ytham W ood , O x f o r d d u r i n g th e w in t e r o f 1985-86. T h e y w e re

p la c e d in t r a n s p a r e n t p la s t i c b u t t e r d is h e s ( 10cm d ia m e t e r , 4cm

d e e p ) c o v e r e d w ith m u s l in . T h e d is h e s w e re p la c e d in an

o u t s id e i n s e c t o r y . If th e m o th s had m ated p r i o r to b e in g

c a u g h t , t h e y u s u a l l y la id t h e i r e g g s on th e m u s l in c o v e r i n g o f

th e b u t t e r d i s h e s .

T h e e g g s w e re c o l le c t e d from th e d is h e s a n d k e p t well v e n t i l a t e d

a n d m o is t , a g a in in p la s t i c b u t t e r d i s h e s in an o u t s id e i n s e c t g r y

u n t i l 28th A p r i l 1986. T h e e g g s w e re th e n m o v e d in to a

c o n s t a n t te m p e r a t u r e room a t 1 5 ° C , 70% r e l a t iv e h u m i d i t y a n d 16

h o u r s d a y le n g t h in o r d e r to i n d u c e h a t c h i n g .

N e w ly h a t c h e d la r v a e w e r e p la c e d in a la r g e p la s t ic c o n t a i n e r

a n d fe d f r e s h y o u n g le a v e s . W ith in 48 h o u r s o f b e in g p la c e d in

th e c o n s t a n t t e m p e r a t u r e room t h e m a jo r i ty o f e g g s h a d h a t c h e d .

T h e la r v a e w e re r a n d o m ly a l lo t t e d to c o n t r o l s o r t r e a t m e n t s .

E a c h t r e a tm e n t c o n s i s t e d o f o n e h u n d r e d l a r v a e . T h e l a r v a e in

e a c h t r e a tm e n t w e r e d i s t r i b u t e d e q u a l ly b e tw e e n te n b u t t e r

d i s h e s . T h e t w e n t y b u t t e r d i s h e s w e re th e n p o s i t io n e d r a n d o m ly

in an o u t s id e i n s e c t o r y . T h e la r v a e w e re fe d d a i l y , a n d th e

d is h e s m o n ito r e d r e g u l a r l y to e n s u r e th a t a t no tim e la r v a e w e r e

w it h o u t f o o d . T h i s n e v e r o c c u r r e d .

T h e s u r v i v a l o f th e la r v a e in e a c h t r e a tm e n t w as m o n it o r e d a n d

th e d a te o f p u p a t io n r e c o r d e d f o r e a c h i n d i v i d u a l . T h e p u p a e

w e re w e ig h e d u s in g an U n im a t ic CL41 b a la n c e as so o n as th e

c u t i c le h a d h a r d e n e d s u f f i c i e n t l y to e n s u r e th a t no d a m a g e

o c c u r r e d d u r i n g h a n d l i n g . W e ig h in g a lw a y s to o k p la c e w i th in

12 h o u r s o f th e b e g in n in g o f p u p a t io n .

1 8 5

B i r c h

N e w ly b u r s t b u d s o f B e t u la p e n d u la w e re c o l le c te d fro m

H ell W o o d , S i lw o o d P a r k b e tw e e n 1 s t - 3 rd M a y 1986. T h e b u d s

v a r i e d in p h e n o l o g y , from le a v e s w h ic h w e re j u s t u n f u r l e d to

f u l l y o p e n e d co m p le te y o u n g le a v e s . A l l th e le a v e s w e re p la c e d

in p o l y t h e n e b a g s a n d f r o z e n a t - 1 1 ° C . T h e s e le a v e s c o n s t i t u t e d

th e t r e a tm e n t d ie t .

T h e c o n t r o l d ie t c o n s t i t u t e d JB. p e n d u la le a v e s c o l le c t e d from H ell

W o o d , S i lw o o d P a r k on M o n d a y s fro m 5th M a y - 30th J u n e 1986.

T h e s e le a v e s w e re f r o z e n a t - 1 1 ° C f o r o n e w e e k a n d th e n fe d to

th e c o n t r o l la r v a e d u r i n g th e fo l lo w in g w e e k . T h e c o n t r o l le a v e s

w e r e t h e r e f o r e f r o z e n fo r s i x to tw e lv e d a y s b e f o r e la r v a l

f e e d i n g . A l l le a v e s w e re r e m o v e d f ro m th e f r e e z e r th e a f t e r n o o n

p r e c e e d i n g la r v a l fe e d in g to a l lo w f o r them to th a w c o m p le t e ly .

6 . 2 . i i . c M e a s u r e m e n t o f fo o d q u a l i t y

W a te r c o n t e n t

L e a v e s u s e d to e s t im a te w a t e r c o n t e n t w e re c o l le c t e d fro m H e l l

Wood on 1 2 th & 20th M a y a n d 2 n d & 16th J u n e 1986. O n e a c h

o c c a s io n f i v e le a v e s w e re i n d i v i d u a l l y w e ig h e d w ith in 30 m in u t e s

o f c o l l e c t io n . T h e y w e re th e n p la c e d in p a p e r b a g s in an o v e n

a t 8 0 ° C . T h e le a v e s w e re w e ig h e d d a i ly to c o n s t a n t w e ig h t .

T o u g h n e s s

F o u r le a v e s w e re c o l le c t e d on 12th & 2 0 th M ay a n d 2 n d & 16th

J u n e . E a c h le a f w as p la c e d b e t w e e n tw o p e r s p e x s h e e ts (a & b

o n F i g . 6 .1 ) . T h e le a f h o ld in g a p p a r a t u s w as th e n b a la n c e d o n tw o

p ie c e s o f w ood 50cm a b o v e t h e b e n c h ( F i g . 6 .2 .) . A p u s h - p u l l

f r u i t t e s t e r ( J o h n C h a t i l lo n & S o n s I n c . , New Y o r k , C a t . n o .

516-1000) w as u s e d to m e a s u r e le a f t o u g h n e s s . F o u r t o u g h n e s s

r e a d i n g s w e r e t a k e n fro m e a c h le a f : tw o f ro m e a c h s id e o f th e

m id r ib (s e e F i g . 6 . 2 ) . C a r e w a s ta k e n n o t to in c lu d e a n y m a jo r

v e i n s in t h e a r e a o f le a f t e s t e d .

F ig 6 .

F ig 6 .

L e a f h o ld in g a p p a r a t u s fo r m e a s u r in g le a f t o u g h n e s s .

A r r a n g e m e n t o f lea f h o ld in g a p p a r a t u s d u r i n g

m e a s u r e m e n t o f le a f t o u g h n e s s .

In se t : p o s i t io n o f t o u g h n e s s m e a s u r e m e n t o f le a f ,

o = p o s i t io n o f m e a s u r e m e n t .

1 8 6

FIG 6.1

FIG 6.2

T

Penetrometer

Leaf holding apparatus

Wooden block

Bench

1 8 7

N it r o g e n a n d t a n n in c o n t e n t

T w e n t y le a v e s c o l le c t e d on 3 r d M a y , 2nd J u n e a n d 18th J u n e

w e re f r e e z e d r ie d in an E d w a r d s F r e e z e d r i e r u s i n g p h o s p h o r u s

p e n t o x id e as a d e s s i c a n t a n d th e n p la c e d in a f r e e z e r a t - 1 1 ° C .

D u r in g N o v e m b e r 1986 th e le a v e s w e re g r o u n d to a p o w d e r u s i n g

a b a ll g r i n d e r . T h e p o w d e r e d le a v e s w e re s t o r e d in p o l y t h e n e

to p p e d g la s s tu b e s in a r e f r i g e r a t o r at 5 ° C u n t i l a n a l y s i s .

N i t r o g e n c o n te n t

T h e tota l n i t r o g n c o n t e n t o f th e leaves w as c a lc u l a t e d b y a

K j e ld h a r m eth o d (s e e A p p e n d i x 2 ) .

T a n n i n c o n t e n t

T h e ta n n in c o n t e n t o f th e le a v e s w as e s t im a te d b y VVint’ s m e th o d

f o r th e e s t im a t io n o f th e n u t r i t i v e in h ib i t o r c o n t e n t o f th e h o s t

p la n t le a v e s ( S . M c N e i l l & V . C . B r o w n , p e r s . c o m m .) ( s e e

A p p e n d i x 2 ) .

6 . 2 . iii R e s u lt s

6 . 2 . Mi. a M o th s

T h e s u r v i v a l o f c o n t r o l l a r v a e to p u p a t io n w as s i g n i f i c a n t l y

g r e a t e r th a n th a t o f t r e a t m e n t la r v a e ( T a b le 6 . 1 , b in o m ia l t - t e s t ,

t = 3 . 9 5 , P < 0 . 0 0 1 ) . T h e s u r v i v a l o f p u p a e to e m e r g e n c e

s h o w e d a s im ila r p a t t e r n . S i g n i f i c a n t l y m ore t r e a t m e n t p u p a e

d ie d th a n c o n t r o l p u p a e (2 x 2 c o n t i n g e n c y t a b l e , Y a t e s

c o r r e c t e d \ 2 = 9 . 6 4 , P < 0 . 0 1 ) ( E v e r e t t 1977).

T h e mean p u p a l w e ig h t o f t h e c o n t r o l la r v a e w as s i g n i f i c a n t l y

g r e a t e r th a n th a t o f t r e a t m e n t la rv a e ( F i g . 6 . 3 ) (o n e w a y

A N O V A , F ^ 7 2 ) = 8 *0 9 6 ' p < 0 . 0 1 ) . When th e s e x o f t h e p u p a e

w as ta k e n in to a c c o u n t ( F i g . 6 . 4 ) it ca n be s e e n t h a t fe m a le s in

b o th t r e a tm e n ts w e re s i g n i f i c a n t l y h e a v ie r th a n t h e m ales ( o n e

w a y A N O V A , t r e a t m e n t F ^ ^ ) = 4 *2 6 , P < 0 . 0 5 , c o n t r o l F ^ ^

= 5 . 2 3 , P < 0 . 0 5 ) . Fe m ale c o n t r o l p u p a e w e r e h e a v i e r th a n

1 8 8

D ie t

C o n t r o l T r e a t m e n t

N u m b e r o f la r v a e 100 100

N u m b e r p u p a t in g 50 *** 24

N u m b e r o f p u p a e

p r o d u c i n g a d u lt s

47 15

N u m b e r d y i n g as p u p a e 3 * * 9

T a b l e 6.1

S u r v i v a l o f E . d e fo l ia r ia la r v a e on d ie ts o f y o u n g B . p e n d u l a

le a v e s ( t re a tm e n t) a n d n o r m a l ly a g in g le a v e s ( c o n t r o l ) .

A s t e r i s k s r e p r e s e n t le v e l o f s i g n i f i c a n c e , ** P < 0 . 0 1 , *** P <

0 . 0 0 1 ) .

D ie t

C o n t r o l T re a tm e n t

N u m b e r o f la rv a e 30 30

N u m b e r p u p a t in g 20 N . S . 15

T a b l e 6 .2

S u r i v a l o f E . d e fo l ia r ia l a r v a e on d ie ts o f f r e s h B . p e n d u l a

le a v e s ( c o n t r o l) a n d on le a v e s f r o z e n fo r 24 h o u r s p r i o r to la r v a l

f e e d in g ( t r e a t m e n t) . ( N . S . = n o t s i g n i f i c a n t l y d i f f e r e n t ,

P = 0 . 2 9 ) .

F ig 6 . 3 M e a n p u p a i w e ig h t (m g) o f E . d e f o i ia r i a on c o n t r o l a n d

t r e a t m e n t d i e t s . B a r s a r e s t a n d a r d e r r o r s . N u m b e r s

a r e s a m p le s i z e .

1 8 9

FIG 6.3

F i g 6 .4 M ean p u p a l w e ig h t (mg) o f male a n d fem ale

EE. d e f o l ia r ia on c o n t r o l a n d t r e a tm e n t d i e t s .

T r e a t m e n t d ie t r e p r e s e n t e d b y h a t c h i n g . B a r s a r e

s t a n d a r d e r r o r s .

190

FIG 6.4

E\\1 TREATMENT I I CONTROL

191

treatment females, but the difference was not significant (one way ANOVA, = 2.16, P > 0.05). Male control pupaewere significantly heavier than treatment males (one way ANOVA, F^ ^ j = 5.68, P < 0.05). The development rate

(inverse of time in days from hatching to pupation) of control insects was significantly higher than that of treatment insects (one way ANOVA, F(1 y2) = 67.08, P < 0.01) (Fig. 6 .5).

6 . 2 .iii.b Food quality

It can be seen from Fig. 6.6 that the wet weight of Betulapendula leaves increased between the first and final sampling

-4 -3date (wet weight = 8.98 x 10 date + 1.35 x 10 , r = 0 .9 /7 , P < 0.05). Little increase in wet weight occurred between sampling dates three and four. The dry weight of the leaves increased throughout the sampling period (regression slope is positive and significant, P < 0.03 (one-tailed)). The water content of the leaves decreased throughout the sampling period (dry wt. = 2.24 x 10“3 date + 2.984, r = 0.98, P < 0.05). Date explained 82% of the variation about the regression line.

Leaf toughness increased with time and varied significantly

between dates (two way nested ANOVA, ^ (3 37) = 188.77, P < 0.001) (Fig. 6 .7 ). However, there was no significantdifference in toughness between individual leaves on a single date (two way nested ANOVA, F ^ 37) = 2.20, P > 0.05).

Leaf total nitrogen (mg/g leaf dry weight) decreased during thesample period (nitrogen = -0.641 date + 42.74, r = 0.999, P <0.05) (Fig. 6 . 8). Tannic acid equivalents increased throughout

-5the sampling period (Fig. 6.9) (% tannic acid = 5.989 x 10 date + 2.337 x 10“2, r = 0.95, P < 0 .05).

Fig 6.5 Mean development time (days) for E . defoliaria on control and treatment diets. Treatment represented by shading.

larvaediet

192

FIG 6.5

a

26

24

2220

18

16

14

12

10

8

6

4

2

038 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56

LARVAL DEVELOPM ENT TIME(days)I [CONTROL TREATMENT

Fig 6. Mean wet and dry weight (g) of iB. penduia leaves during spring and early summer.

193

FIG 6.60.15 - r 0 .14 -

0.01 -

0 - i I " ' i i

M A Y 12 M A Y 20 JU N E 2 JU N E 16

SA M PLIN G D A TE (1986)

+

—100

— 50

o

WET WEIGHT % WATER DRY WEIGHT

WATE

R CON

TENT

S fres

h weig

ht)

Fig 6.7 Mean leaf toughness (g/cm) of 13* pendula spring and early summer as measured penetrometer. Bars are standard errors.

duringby a

260240220

200180160140120

100

80604020

0

194

FIG 6.7

Fig 6 . Total leaf nitrogen (mg/g dry wt) of B . pendula during spring and early summer.

195

FIG 6.8

Fig 6.9 Percentage tannic acid equivalents as measured by Wint's method of E3. pendula leaves during spring and early summer. Bars are standard errors.

196

FIG 6.9CO

0.03 - r

0.029 -

W 0.028 -

0.027 -

aw 0.026 -euc 0.025 -u 0.024 -1 0.023 -

0.022 -

0.021 -

0.02 -■MAY 3 JUNE 2 JUNE 18

SAMPLING DATE (1986)

6.3 Experiment 2

THE EFFECT OF THE FREEZING OF 3. PENDULA LEAVESON LARVAL GROWTH

6.3 .i Aims

The aims of this experiment were to determine whether freezing birch leaves prior to larval feeding had any effect on the performance of the larvae.

6 .3 .ii Materials and Methods

6.3.11. a Moths

Sixty newly hatched jE. defoliaria larvae were placed randomly in six plastic butter dishes on 23rd April 1987. Each dish contained ten larvae. Three dishes were allocated at random to a treatment diet and the remaining three dishes were controls. The larvae were kept in an outdoor insectory until they pupated and were fed treatment and control diets daily. The dishes were monitored throughout the day to ensure that food was always available (this was always the case).

The date of pupation and the pupal weight for each larvae was recorded as before. The survival of larvae in each dish was also monitored.

6.3.11. b Food

Each day from 23rd April 1987 E$. pendula leaves were collected from trees in Silwood Park. Half of the leaves were allocated to the control diet and half to the treatment diet. The control leaves were fed to larvae within 30 minutes of being collected. The treatment leaves were frozen at - 11°C for 36 hours before being thawed for 12 hours and then fed to larvae.

198

6.3. iii Results

It can be seen from Table 6.2 that survival to pupation did not differ significantly between the two diets OL2 2 by 2 contingency table, Yates' corrected X 2 = 1.1, P = 0.2949). The development rate did not vary significantly between larvae on the two diets (two way ANOVA, = 1.48, P = 0.234), and there wasno difference in development rate between the sexes (two way

ANOVA, F^ 2Q) = 1*36, P > 0.05) (Table 6 .3 ). Pupal weight did not vary significantly between treatments (two way ANOVA,

^(1 27) = P = 0*277). In both treatments the pupal weightof females was significantly higher than males (two way ANOVA, F( 1 = 10.73, P < 0.05).

6.4 Experiment 3

INVESTIGATION OF THE EARLY SPRING PHENOLOGY OF E. DEFOLIARIA

6.4 .i Aims

The aims of this investigation were to examine the relationship between the hatching of E. defoliaria and the phenology of the tree relative to other spring feeding Lepidoptera larvae. E. defoliaria larvae are quoted in the literature as being spring feeders (South, 1908; Scorer, 1913). This investigation was carried out to determine whether E. defoliaria larvae in the field normally feed on newly burst buds and very young leaves; that is leaves of a similar age to those constituting the treatment diet in the main experiment.

6 .4 .ii Methods

One hundred birch branches were marked in Hell Wood, Silwood Park as part of the major field experiment (see section 2 .1 ). These branches were utilised in this investigtion. Every few days between 24th April 1987 and 27th May 1987, ten of the marked branches were randomly selected and sampled with a beating bag. No branch was sampled twice. All Lepidoptera

199

DIET

T reatment Control

Mean development rate £.13 x 1C “ P 3.54 x 10 N. S. 2.04 x 10~ 2 ± 3.54

Mean pupal weight 87.72 0 2.33 N.S. 84.06 1 2.33

Mean pupal weight of females 91.25 P 4.19 N.S. 91.35 = 3 .19

Mean pupai weight of males C4.19 ± 2.57 N.S. 76.77 - 4.48

Table 6.3

Pupal weight (mg) and larval development rate (inverse of days from hatching to pupation) of E. defoliaria fed fresh j3. penaula leaves (control) and leaves which had been frozen for 24 ho

(treatment). (Mean i 1 S .E . , In = 30, N .S . = not significantly different.)

2 00

larvae collected were identified as accurately as possible. The date of the first burst on birch in Hell Wood was also recorded.

6 .4. i i i Results

Bud burst of birch was recorded in Hell Wood on 20th April 1987 and as Figure 6.10 shows, E. defoliaria larvae were first recorded on 27th April 1987.

The temporal distribution of E. defoliaria larvae was not significantly different from that of other Lepidoptera larvae recorded in the sample (Kolmogrov-Smirnoff statistic = 0 .2 8 , P > 0.05).

6.5 Experiment 4

THE EFFECT OF LEAF TOUGHNESS ON SURVIVAL OF EARLY INSTAR LARVAE

6 .5 . i Aims

The aim of this experiment was to determine whether newly hatched larvae of E. defoliaria could initiate feeding and survive on mature leaves as well as on their normal diet of young leaves. These results should give some indication as to whether leaf toughness is an important factor in determining the larval feeding period of E. defoliaria as suggested by Feeny (1970) for

O. brumata.

6 .5 .ii Materials and Methods

defoliaria eggs, which had been laid during the winter of 1987, were placed in a refrigerator at 5°C on 25th March 1987. This served to retard their development and prevent hatching. On 28th May 1987 the eggs were removed from the refrigerator and placed in a controlled environment room at 15°C, 70% relative humidity and 16 hours day length. All larvae hatched within 48 hours. Ten larvae were placed in each of two plastic butter dishes. The dishes were placed in an outside insectory and the

Fig 6.10 Abundance of E. defoliaria and other Lepidoptera larvae on E3. pendula during the period immediately following bud burst 1987.

NUM

BER

OF LA

RVAE

201

FIG 6.10

■ E.defoliaria + OTHER LEPIDOPTERA

BUD BURST

202

larvae fed daily with freshly collected j3. pendula leaves. The survival of the larvae was monitored for 7 days beginning on

30th May 1987.

Four leaves of EK pendula were collected from the field on 30th May 1987 and 5th June 1987. The toughness of these leaves was measured as described in section 6 . 2 .ii .c .

6.5. iii Results

After seven days only eight larvae were alive compared with the high survival of larvae fed fresh leaves in Experiment 2 (twenty two out of th irty ). The survival of larvae in this experiment was significantly reduced compared with Experiment 2 (X2 2 by 2 contingency table, Yates' corrected"^2 = 4.25, P < 0.05).

Some larvae had initiated feeding as damage was observed on

some leaves and frass was present in the dishes. However, it was impossible to ascertain which larvae had fed.

The toughness of the birch leaves increased significantly between sampling dates (two way ANOVA, log data as variances were unequal, 35 = 280.82, P < 0 . 001) . Table 6.4 shows that the mean toughness of leaves on 30th May 1987 was three times greater than that of the youngest leaves sampled during 1986 (no measurements of the toughness of young leaves in 1987 were taken, so comparisons were made with samples from 1986).

6.6 DISCUSSION

Contrary to theory (Feeny, 1976; Lawton & McNeill, 1979), E. defoliaria performed better for a range of measures on older leaves, generally regarded as poor quality food, than on young

leaves, which are generally regarded as high quality diet (Feeny, 1970; Rausher, 1981; Lawson et a[, 1982; Raupp & Denno, 1983; Damman, 1987). These results present a paradox with respect to current ecological theory and the life history of E. defoliaria. It seems that accepted theory of what constitutes a diet of high quality e .g . high water content, high nitrogen

203

Date Toughness (q/cm)

12th May 1986

30th May 1987

5th June 1987

58.75 ± 2.61

195.33 ± 11.49

247.92 ± 6.62

Table 6.4

Comparison of toughness of young B_. pendula leaves with that of mature leaves (mean ± 1 .S .E .)

204

levels, low toughness and low defensive chemical levels (McNeill & Southwood, 1978; Feeny, 1976; Rhoades & Cates, 1976) does not hold when applied to E. defoliaria. No explanation can be provided for this, although it is relevant to note current dispute on the role of quantitative defences in plant/herbivoreinteractions (Bernays, 1978, 1981 ; Moran & Hamilton, 1980;Zucker, 1983).

In view of these unexpected results, it is important to consider the experimental procedure. The experimental design was similar to that used by Feeny (1970) who fed previously frozen oak leaves to O. brumata, but obtained different results from those obtained here. The experiment was carried out under artificial conditions in the laboratory using excised leaves, both of these factors may influence the plant/herbovore interaction. The use of previously frozen leaves may also have affected the interaction.

Several of these potential problems were tested in individual experiments. Firstly, the effects of fresh and previously frozen leaves on defoliaria were tested (Experiment 2) and no differences were found. Secondly, the relative phenology of the host plant and larvae in the field (Experiment 3) revealed that the leaves offered in the experiments were a normal source of food for E. defoliaria.

Given that the experimental procedure was appropriate, two biological explanations for the observed results can be presented. Firstly, there could be a chemical (or chemicals) present in the buds and/or very young leaves, which providing the larvae were subjected to this for a short period had little effect on larval performance. However, if larvae are forced to feed on such food for" longer periods the effects are detrimental. The chemical could perhaps be acting in a dosage-dependent manner. Such a hypothesis would be compatible with the idea that plants defend their tissues in relation to their apparency (Feeny, 1976). For example, unapparent tissues (buds and young leaves) are optimally defended by qualitative defences, whereas more apparent plant parts (mature leaves) are best

205

defended by quantitative defences (Feeny 1976). Fowler (1984) found that "unapparent" seedlings of B_. pendula were less well defended by quantitative defences than more "apparent"saplings. No attempt was made, however, to examine thequalitative defences of seedlings and saplings. The idea that any such chemical would act in a dose-dependent manner, as suggested by these results, does not agree with theory on the action of qualitative defences (Feeny, 1976).

The second explanation of the results is that later instars of E. defoliaria larvae require some nutritional factor in quantities not present in young leaves, but which are present in mature leaves.

Neither of these hypotheses can be tested with the results available. It is interesting to note, however, that other workers have found that E. defoliaria behaves in a similar manner. S. Hartley (cited in Lawton, 1986) found using choice chambers that E. defoliaria preferred damaged foliage to undamaged foliage. Theory concerning rapidly induced chemical defence (Edwards & VV ratten, 1985; Fowler & Lawton, 1985; Haukioja £ Hanhimaki, 1985) predicts that damaged tissue contains a greater concentration of phenolic compounds than undamaged tissue. However, in view of the current debate on the importance of induced defences, it may be best not to read too much into that result; it is interesting to note, however, that other moths tested (0 . brumata, Apocheima pilosaria and Euproctis similis,

showed no preference between damaged and undamaged foliage, or preferred undamaged foliage. Haukioja ( pers. comm.) reports that E. defoliaria preferred mature foliage to immature foliage.

It is concluded that no obvious explanation for the above results can be presented. Clearly E. defoliaria shows interesting behaviour and there are several hypotheses which require testing before the situation will be clarified. The results also point to other questions about the life histoy strategy of E. defoliaria. Given that it does perform better on older leavesthan on young ones, why then do the larvae emerge so early in

206

the season when young leaves constitute the only food source?

There could be several pressures selecting for early spring larval emergence apart from the presence of higher quality food in the spring. By having a life cycle in which larvae emerge in spring, the moth could be reducing potential parasitism orpredation on one of the life states. Ekanoyake (1967) showedthat the key factor in the population dynamics of E. defoliaria was "winter disappearance", defined as the difference between the log number of eggs/m2 and the log number of fully developed larvae falling to the ground. Winter disappearance accounted for 76% of total mortality. The major mortality factor contributing to winter disappearance was the asynchrony between caterpillar hatching and bud burst. This could be lessened ifthe eggs hatched later in the season. This suggests thatpresence of a large selective pressure for larvae to hatch in early spring. EkanoyaVe (1967) found that larval mortality due

to parasitoids, predators and disease accounted for 5.8% of total mortality. Pupal mortality accounted for 18% of the total mortality; this means that only 10% of larvae pupating emerge as adults. (Adult mortality was assumed to be negligible). This key factor analysis suggests that it is the pupal stage which is most susceptible to predation. Perhaps if the pupae were in the soil at a different time of year they would suffer even greater mortality. Such a hypothesis is easily testable.

Another pressure which could perhaps select for spring larval feeding would be escaping interspecific competition. This seems unlikely as herbivore density is at its peak during spring. Few authors have found interspecific competition to be an important structuring force in herbivorous insect communities (Lawton & Strong, 1981), but Karban (1986) presents evidence suggesting interspecific competition could be important to insect herbivores.

It has been shown here (Experiment 4) that first instar larvae survive less well on mature foliage than on young leaves. Unfortunately, the sample size in this experiment was small, but nevertheless it provides an important insight into understanding the life-cycle strategy of E. defoliaria. Clearly, if early instars

207

are unable to feed on mature foliage then it is imperative that they hatch in early spring and feed on young foliage. It seems that, as suggested by Feeny (1970) and Kraft & Denno (1982), the seasonal increase in leaf toughness is the reason for early spring feeding by JE. defoliaria.

As stated in the introduction, if quantitative defences are to affect the population dynamics of a herbivore, they must either reduce survival, reduce fecundity or increase generation time. Experiments which claim to show an effect of quantitative defences on insect herbivores can usually demonstrate an effect on the first two parameters. Reduced fecundity is usually demonstrated by showing reduced pupal weights on specific diets and assuming insect body weight is positively correlated with fecundity as shown by Miller (1957), Cook (1961) and Haukioja & Neuvonnen (1985). An increase in larval development time does not necessarily result in that individual having an increased generation time. Such a statement can only be made if larval development time is positively correlated with a longer pupal development time. This has never been demonstrated.

it is also important to consider the relevance of an increase in development time of a matter of days as shown here and by Hough & Pimentel (1978). In univoltine insects, such as most spring feeding Lepidoptera it is difficult to see how an increase in development time of a few days can have an effect on the population dynamics, as the number of generations per year will remain unaffected. There could, however, be effects on the mortality of the larvae, and it has been suggested that increased development times could lead to increased predation or parasitism (Feeny, 1976; Moran & Hamilton, 1980; Price et aj_, 1980). However, Clancy & Price (1987) and Dammon (1987) conclude that longer development time does not necessarily lead to greater predation.

I would like to suggest that the situation may be complex and that a series of trade-offs could be occurring. For example, if death per unit time of larvae was lower than death per unit time of pupae then, assuming all other things to be equal, it could be

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advantageous for an individual to prolong its larval development time. The data on the population dynamics of E. defoliaria(Ekan^yrke, 1967) suggests that such a mechanism would be feasible in EE. defoliaria. If such trade-offs do occur then we need to rethink the analysis of experimental data and theories of plant/animal interactions.

6.7 CONCLUSION

E. defoliaria larvae consistently perform better on what theory predicts should be a poorer diet than on a good diet. Noexplanation can be given to explain these results. It issuggested that leaf toughness is important in selecting forspring feeding in E. defoliaria. No evidence is provided in support of the theory that quantitative defences can reduce the intrinsic rate of increase of an insect herbivore.

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CHAPTER SEVEN

GENERAL DISCUSSION

This thesis aimed to test a specific hypothesis in which the absolute abundance of insect herbivores was predicted to change in relation to the successional age of the habitat (Lawton & McNeill, 1979). This hypothesis and several related topics were examined in Chapter 4, but prior to this, in Chapter 3, patterns in the communities used to test the hypothesis were described. In many respects this analysis confirmed the now well- documented changes in plant and insect communities which occur during succession (Cray, Crawley & Edwards, 1987; Til man, 1988 and references therein), together with a somewhat surprising constancy in insect species richness and abundance between the two years of sampling. In Chapter 5 it was seen that certain attributes of the successional communities may affect the relative and absolute abundance of some insect species. It was, however, difficult to analyse the effects of community attributes individually as they were often interrelated. Even so, an awareness of the interrelatedness of the various community attributes, and a realisation of the difficulty inherent in measuring such attributes is considered preferable to a consideration of any one attribute in isolation which may lead to a false interpretation of the observed patterns of insect abundance. Chapter 6 aimed to examine one aspect of the original hypothesis under controlled laboratory conditions, where confounding influences of the surrounding community were absent. The results of this section were unexpected, and despite following the methodology of Feeny (1970), gave completely different results. Although controlled laboratory experiments are of great value in ecology, when the results are contradictory to accepted theory some difficulty remains in their interpretation, since the artificial environment of the laboratory may be considered a confounding factor. The unexpected results described in Chapter 6 emphasise that even in a well-studied system such as birch (Fowler, 1984, 1985; Fowler & MacGarvin, 1986; Hartley, 1988; Hartley & Lawton, 1987; Haukioja, Niemeia, Isolivar'v, Ojala & Aro, 1978; Haukioja,

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Niemela & Isolivari, 1978; Haukioja & Niemela, 197&; Niemela, Aro

& Haukioja, 1979; Haukioja & Niemela, 1976, Ayres & Maclean 1987), there remain questions which will only be answered by a combination of experimentation in the field and laboratory.

The results of this work show unequivocally that the absolute abundance of herbivores feeding on plants defended by qualitative chemical defences is greater than that of herbivores on plants defended by quantitative chemical defences. However, some accounts in the literature contain information contrary to these results and these must be considered before the current work is taken as vindication of plant/herbivore theory as proposed by Feeny (1976) and Rhoades & Cates (1976), and as understood by Lawton & McNeill (1979). To date little work has been undertaken on the relationship between qualitative defences

and adapted insect herbivores, with some results suggesting that there may be effects on herbivore performance eg weight (Dirzo & Harper, 1982), growth rate (Erickson & Feeny, 1974; Scriber 1981), survival (Harley & Thorsteinson, 1967) and fecundity (I.M . Evans pers. comm.). Such reductions in individual performance may well be translated into effects on population densities by similar mechanisms as those postulated for quantitative defences (Lawton & McNeill, 1979). Also, it is now far from certain that tannins act on all herbivores in the manner suggested by Feeny (1976) (eg Berenbaum, 1983; Bernays, 1978, 1981; Chan, Waiss, Binder & Ellinger, 1978; Lawson et al, 1982, 1984; Manuwoto & Scriber, 1986; Schweitzer, 1979). On the other hand there is some evidence that herbivores are affected in some way by tannins (Bennett, 1965, Bernays, 1978; Berenbaum, 1983; Chan et a[, 1978; Feeny, 1968, 1970; Manuwoto & Scriber, 1986, Roehrig & Capinera, 1983;Schweitzer, 1979). Consequently, there is considerable difficulty in interpreting this contraditory evidence, and there is a considerable need for good biochemical experimentation in ecology (see Martin & Martin, 1982). Methods, such as those of Hartley (1988), where phenolic production was prevented by blocking essential enzymes in the Shikimic pathway, could provide a novel experimental tool. The present controversy over the effects of chemical defences on We«\>ivores poses questions

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about the rationale underlying the hypothesis tested here. Lawton & McNeill's (1979) prediction of different agedsuccessional communities having characteristic levels of insect herbivore abundance are confirmed by the results of the present study and, in the absence of good contradictory evidence, it must be assumed that their initial assumptions on the effects of chemical defences on insect herbivores were correct. It ispossible hov/ever, that observed patterns of abundance were due to predation and not solely to plant chemistry. The importance of predators in herbivore population dynamics is evident from the literature on biological control (De Bach, 1974; Huffaker, 1980). The data from biological control is often obtained from unusual circumstances, although data from natural popuations confirms the importance of predation and disease in herbivore dynamics (Anderson & May, 1980, 1981 ; Buckner & Turnock, 1965; Ekanoyake, 1967; Holmes, Schultz & Nothnagle, 1979; Ohgushi & Sawada, 1985; Varley, Gradwell & Hassell, 1973 and references therein).

Little work on variation in predation pressures and efficiency between community types has been undertaken, although available data demonstrates considerable variation between habitats (Ohgushi & Sawada, 1985; Eickwort, 1977). Both of these studies equate higher levels of predation with a greater diversity of background vegetation maintaining predator numbers. These studies did not, however, consider differences in predation between woodland and herbacious communities, and in the absence of such data one cannot speculate on the possible impact of such a phenomenon on herbivore abundance: it remains an important and potentially productive avenue of research.

The lower absolute abundance of herbivores on late successional plants does, however, suggest that some aspect of their chemistry reduces the intrinsic rate of increase, r , of their hervivores to a greater degree that that of early successional plants. It is not possible to say whether early successional plants have any effect on the intrinsic rate of increase of their herbivores. It is apparent from Chapter 5 that other aspects of the environment may affect the absolute abundance of certain species. Such results suggest that local variation in community

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attributes, such as predation pressure, vegetation structure

and soil nutrients may be important. The importance of vegetation structure was difficult to ascertain from the results of the analysis in Chapter 5, although it is clearly important to some species, and could be interacting with variation in predation pressure. Soil nutrients have been shown to have an effect on herbivore abundance (Prestidge & McNeill, 1983; Onuf, Teal & Valiela, 1977). and are "the principal effect of habitat on average food quality" (Crawley, 1983). However, increased nutrient levels need not necessarily lead to greater herbivore densities (Auerbach & Strong, 1981; Wilcox & Crawley, 1988). Any combination of these three factors could affect patterns of herbivore abundance between serai stages and are worthy of further study.

There are several weaknesses in this study. Firstly, the host plant records, which are crucial to the calculation of absolute abundance, were of necessity extracted from the literature and are almost certainly subject to error. Consideration of both absolute abundance by host plant family and species helped nullify such errors, but which of these two measures is most likely correct, may vary from species to species. Records of the larger, more consipicuous species are more likely to be complete and reliable, so for Chrysomelidae, most Heteroptera and some weevil species absolute abundance by host plant species is probably the best measure, although within certain weevil genera where there are known taxonomic difficulties, eg Apion and

C^uV^orhynchus, it is probable that host plant specificity is less accurate. In the case of grass-feeding species, absolute abundance by host plant family is undoutedly the best measure, since relatively few records distinguish between grass species. For each group, however, absolute abundance utilising both measures was greater on early successional plants than on late successional species. The second major problem with the system studied here is the lack of replication in space. Due to constraints on land availability only one site of each age is initiated every year. Statistically, this results in differences between serai stages which may be purely site differences, as site and serai stage are confounded variables (Hurlbert, 1984).

213

Intuitively, however, it seems that observed differences are the

result of the different community types on each site, and theconstancy of the results over time reinforces this assumption. Thirdly, this study only considered a limited range of plant and insect species over a relatively short time span. In this context it would be interesting to consider the absolute abundance of herbivores on a range of late successional plant species to confirm the consistency of these results, as it remains possible that birch may be peculiar in its relationship with its herbivores. Further study in several geographic regions over longer timespans would provide a better test of Lawton & McNeill's (1979) hypothesis. Finally, all hervivores were assumed to be folivores. This is not strictly true as somespecies may feed at least in part on flowers and/or seeds. Literature records are generally unclear as to the specific plant tissue utilised by a species, and no indication of preference for the different plant parts is available.

This study has tested a hypothesis under field conditions using a novel technique. The measurement of absolute abundance, at the scale used here, is to my knowledge unique and demonstrates a powerful tool for comparisons between communities. If the interpretation of the results andassumptions of Feeny (1968, 1970, 1976) on the action of tannins had been accepted without controversy, this thesis could be seen as good evidence for his theories, and those of Rhoades & Cates (1976). In view of the recent controversy however, itscontribution to ecological theory is less clear. The results of this thesis do, however, add considerable weight to the view

that qualitative and quantitative defences have very different effects on herbivore performance and population dynamics. Only after a better understanding of the mechanisms and effects of chemical defences on herbivores, and the relative importance of their predators, will it become clear whether chemical defences are the prime determinants of characteristic levels of abundance of insect herbivores.

"The common view that low nutritive quality of plant tissue is an antiherbivore adaptation must be allowed as plausible, but it remains uncertain. It will be hard to refute". (Moran &

Hamilton, 1980).

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ACKNOWLEDGEMENTS

I would like to thank my supervisor, Dr. V .K . Brown, for her continued help and guidance, and Professor M.P. Hassell for allowing me to use the facilities available at Silwood Park. Statistical advice was freely provided by M. Rees, T . Ludlow, M. Crawley, A. Cange and C. Godfray. Taxonomic difficulties were overcome with help from P. Kirby, P. Hyman, M. Cox andJ. Hollier. I would like to thank the many people who provided field assistance, especially to intrepid D-Vac assistants, Bernie Briscoe, Simon Pilchard, Charlotte Ford and Debbie Pro< rer, and to Mr. H .A . "Levitt and his technical staff for all their help. I greatly appreciate the interesting and valuable conversations held with Drs. A. Gange, S. McNeill, M. Crawley, C. Godfray, S. Hartley, S. Fowler and A. Le Masurier. Special thanks for the many stimulating discussions with Ian Evans, Mark Rees and Andrew Wilcox and extra special thanks to Helen for her continued support throughout the duration of this project. T his work was financially supported by N .E .R .C . and Charles Square discretionary awards.

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2 3 3Appendix 1

Insect species Host plant Ref.

Hemiptera: HeteropteraAcalypta parvula Short moss. (1)Acetropis gimmerthali Grasses esp. oat grass. (1)Adelphocoris lineolatus Always on Papilionaceae esp.

restharrow, meadow vetchling, milk vetch & clovers. (1)

Aelia acuminata Tall & rank grasses. (1)Agramma leata Sedges & rushes. (1)Amblytylus nasutus Grasses esp. meadow-grass. (1)Berytinus minor Trifolium repens, Ononis

repens. (1)Berytinus montivagus Medicago lupilina. (1)Berytinus signoreti Medicago lupilina, Hippocrepis

canos a. (1)Blepharidopterus angulatus Apple, alder, elm, birch, lime

& other trees. (1)Calocoris norvegicus On growing points, buds,

flowers, & unripe fruits of Urtica, Canpositae (incl. T. inodorum, Senecio, Cirsium) and clovers. (1)

Campyloneura virgula Many trees esp. Crataegus, oak& hazel. (1)

Capsus ater Grasses esp. Lolium perenne,Agropyron repens, also Phleum,Holcus lanatus & others. (1)

Ceraleptus lividus Trifolium pratense, T .campestre, T. arvense. (1)

Chlamydatus pullus Lucerne, sorrel & knotgrass -found on probably black medick & white clover are food plants. (1)

Coreus marginatus Rumex acetosa, R. acetosella,R. crispus, Polygonum persicaria, P. aviculare. (1)

Corianeris denticulatus Medicago lupilina, Melilotusspp., T. arvense. (1)

Cymus claviculus Polygonum aviculare, Juncusbufonius. (1)

Cymus melanocephalus Lotus ulignosus, Lysimachiavulgaris, rushes. (1)

Dolycoris baccarumDicyphus epilobi Epilobium, Chamaenerion spp. (1)Dicyphus errans (1)Drymus brunneus Mosses, fungi & ? (1)Drymus sylvaticus Mnium & other mosses. (1)Elasmucha grisea Birch. (1)Elasmostethus interstinctus Birch. (1)Eurydema oleracea Larvae may be carnivorous seeds

of Alliaria petiolata, Raphanus raphanistrum, Armoracia rusticana & many other crucifers. (1)

Harpocera thoracica Oak. (1)

234

Insect species Host plant Ref.

Heterotana merioptera Much vegetation esp. Urtica many trees & shrubs all stagespredatory. (1)

Ischnodemus sabuleti Deschampsia cespitosa, reeds Arrhenatherum elatius, Glyceria maxima, G. fluitans, D.glomerata (pers obs). (1)

Kleidocerys resedae Birch, alder. (1)Leptopterna dolabrata Grasses esp. timothy, Agropyron

repens, meadow foxtail, Holcuslanatus & Dactylis glcmerata. (1)

Leptopterna ferrugata Grasses esp. red fescue, common bent, wavy hair-grass, oat-grass & meadow grass. (1)

Lopus decolor Agrostis spp. & other grasses. (1)Lygocoris contaminatus Birch, alder occasionally

nettles. (1)Lygocoris pabulinus Hawthorn, apple, currant, plum,

cherry & lime, nettles, creeping thistle, groundsel, dandelion, black nightshade, potato, bittersweet, white deadnettle, sunflower, dock, fat hen, rose-bay willowherb& common cow wheat. (1)

Lygus rugulipennis Many herbaceous plants & shrub esp. Chenopodium album & other Chenopodiaceae, T. inodorum, Rumex spp., Urtica spp.,Trifolium spp. (1)

Miris striatus Oak, alder, willow, elm, hazel,hawthorn & other trees. (1)

Megaloceraea recticomis Grasses. (1)Monalocoris filicis Bracken & ferns. (1)Myrmus miriformis Many species of grass, leaves &

unripe seeds. (1)Neottiglossa pusilla Grasses esp. meadow grass. (1)Notostira elongata Grasses esp. Agropyron repens. (1)Nysius thymi Numerous esp. Composites e.g.

Inula conyza, Erigeron spp.(Conyza) party insectivorous. (1)

Orius niger Heathers, wide range of low plants esp. Artemsia vulgarispredatory. (1)

Pentatcma rufipes Oak, alder & most nativedeciduous trees. (1)

Pantilius tunicatus Hazel, alder & birch. (1)Peritrechus geniculatus Moss & low vegetation. (1)Peritrechus lundi Potatoes. (1)Phytocoris longipennis Deciduous trees esp. hazel, oak

& hawthorn. (1)Phytocoris tiliae All deciduous trees esp. oak,

ash, lime & apple. (1)

235

In se c t sp e c ie s P h ytocoris v a r ip es

Piesma maculatum Pithanus m aerkeli Plagiognathus arbustorum P lagiognathus chrysanthem i

Podops inuncta P sa llu s b e t u le t iP sa llu s f a l l e n i Rhopalus parumpunctatus

Rhopalus subrufusS co lop osteth u s thonsoni Stenodema calcaratum

Stenodema laevigatum

S ten otu s b in o ta tu s

S ty gn o co ris fu l ig in e u s S tygn ocoris p e d e s tr is T in g is am pliata T in g is carduiT rigon oty lu s r u f ic o m is

T ro ilu s lu r id u s T ytthus pygmaeus

Hemiptera: Hanoptera - P s y ll id a eAphalara p olygon iA rytaina g e n is ta eA r y ta in il la sp a r t io p h ila C raspedolepta nervosa

Craspedolepta subpunctata

Host plant Ref.

G rasses e sp . Bromus, Phleum, & T rifo liu m y Rumex, A c h i l le a ,T. inodorum. ( I )Chenopodiaceae (L)G rasses & ru sh es. (1)Many e sp . U rtica spp. (1)S en ecio ja co b ea e, T. inodorum, A c h ille a m ille fo liu m , Medicago l u p i l in a , U r tic a . (1)Rung (saprophage or c a r n iv o r e ) . (L)P a r tly phytophagous on b irch p a r tly predatory on aphids e t c . (L)? U)C r a n esb ill , S t . John's w orts, sp u rrey s, s t o r k s b i l l & cocks­fo o t g r a ss e sp . common mouseear chickw eed. (1)Wild b a s i l , herb Robert e sp .S t . Joh n 's w ort. (I)? n e t t l e s ? (L)G rasses on buds & unripe g ra in s e sp . on A g ro stis & meadow fox­t a i l . (1)G rasses e sp . meadow f o x t a i l , tim othy, red fe sc u e , cannon b ent and wavy h a ir g ra ss e sp . on flo w er in g heads, on buds & g r a in s . (1)G rasses e s p . Phleum & D actyl i s & o c c a s s io n a lly on C anpositae f lo w e r s . (1)? (1 )? (1)Cirsium a rv en se . (1)Cirsium v u lg a r e , Carduus n u tan s, Cirsium p a lu s tr e . (1)G rasses e s p . wavy h a ir g r a ss , common b en t, red fe s c u e , tim othy & o th e r s . (1)T rees , p red ator . (1)Predatory on eggs & nymphs (1)

Polygonum a v ic u la r e , P .amphibium. (2)C y tisu s sc o p a r iu s , C .a u s tr ia c u s , G enista t in c t o r ia . (2)C y tisu s sc o p a r iu s . (2)A c h ille a m ille fo liu m , A.ptarmica, A. gerberi, Artemesiav u lg a r is . (2)Chamaenerion a n g u stifo liu m . (2)

236

Insect species Host plant Ref.P sy lla a ln i Alnus g lu t in o s a , A. incana, A.

v i r i d i s , A. jap o n ica , A.h ir su ta . (2)

P sy lla b etu la e B etu la pendula. (2)P s y lla brunneipennis S a lix spp. (2)P sy lla h a r t ig i B etula pendula, B. pubescens,

B. p la ty p h y lla . (2)P sy lla melanoneura C rataegus. (2)P sy lla pulchra S a lix spp. (2)P sy lla so rb i Sorbus. (2)T rioza abdom inalis Chrysanthemum s p p ., A lch em illa

v u lg a r is agg. (2)T rioza chenopodii A tr ip lex p a tu la , A. h o r te n s is . (2)T rioza remota Quercus robur, Q. p etra ea . (2)T rioza u r t ic a e U rtica d io ic a , U. dubia, U.

u ren s. (2)lip tera : Homoptera - C ic a d e llid a eAdarrus o c e l la r i s G rasses. (3)

Arrhenatherum e la t iu s . (6)Holcus spp. (5)

A g a llia r ib a u t i G rasses. (4)A g a llia venosa G rass. (4)A llygu s carm utatus T rees, sh ru bs, sometimes g r a s s -

land. (8)Aphrodes a lb ifr o n s G rasses.Holcus s p p ., D a c ty lis

(4)glcm erata . (5)

Aphrodes b ic in c tu s G rasses.Holcus s p p ., D a c ty lis

(4)g lcm erata . (3)

Aphrodes b ifa s c ia tu s G rasses. (4)Aphrodes h is tr io n ic u s G rasses. (4)Aphrodes t r i f a s c ia t u s G rasses. (4)A rthaldeus p a sc u e llu s G rasses. (8)

G rasses & Juncus. (6)A g ro stis c a p i l l a r i s . (5)

Athysanus a rgen tar iu s Saltm arshes. (8)Damp meadows & c lo v e r f i e l d s . (6)B a lc lu th a punctata G rasses. (8)Deschampsia f le x u o sa . (5)

C icadula p e r s im il i s Juncus, Carex. (8)In meadows. (6)D a c ty lis g lcm era ta , Holcus sp p . (5)

C ica d e lla v i r i d i s G rasses in marshy p la c e s . (4)Juncus e f fu s u s . (5)

Conosanus o b so le tu s G rasses. (4)D ip loco lenu s abdominal i s G rasses. (8)

G rasses. (6)Holcus spp. (5)Doratura s t y la t a F ie ld s & meadows, Narduss t r i c t a .A g ro stis c a p i l l a r i s , Festuca

(6)rubra. (5)

237

Insect species Host plant Ref.

Elymana su lp h u r e lla G rasses. (8)Holcus m o l l i s , Phleum p r a te n se , g r a ss e s . (6)Holcus spp. (5)E u sce lis in c is u s G rasses. (8)

E u sce lis l in e o la tu s G rasses. (8)Graphocephala fen n ah i Rhododendrons. (4)Graphocraerus v e n t r a l is G rasses. (8)

Poa p ra te n s is & Anthoxanthum odoraturn. (6)

I s su s co leo p tra tu s iv y , h o lly & v a r io u s tr e e s orin moss. (7)Lam pottetix octop u n cta tu s T rees. (8)

M acropsis s c u t e l la t a N e t t le s . (4)M acrosteles c r i s t a t u s Clover f i e l d s , in p o ta to f i e l d s ,

Polygonum, Linum. (8)M acrosteles la e v i s G rasses, o a t s , b a r le y , Loliumperenne. (8)A g ro stis c a p i l l a r i s . (5)M acrosteles sex n o ta tu s G rasses & c lover? (8)

Megophthalmus sca n icu s Grass r o o ts & bu sh es. (4)M ocydiopsis parvicauda G rasses. (8)O ncopsis f l a v i c o l l i s B etu la . (4)O ncopsis subangulata B etu la pendula. (4)O ncopsis t r i s t i s B etu la . (4)Psammotettix c o n f in is G rasses. (8)

Arrhenatherum e l a t i u s . (6)A g ro stis c a p i l l a r i s . (5)

R e c i l ia co ro n ifera Short g r a s s e s . (8)Holcus spp . (5)T ach ycix iu s p i lo s u s

Tham notettix c o n f in is T rees & lower v e g e ta t io n . (8)B etu la , w illow s & h erb s. (6)

Tham notettix d i lu t io r Oaks, other t r e e s , lower v eg e ­t a t io n . (8)Q jercus. (6)

Hemiptera: Hctnoptera - C ic a d e llid a e , subfam ily TyphlocybinaeAlebra a lb o s t r i e l la Quercus, A ln u s. (3)A ln e to id ia a ln e t i A ld er, h a ze l & oth er t r e e s . (3)A rborid ia r ib a u t i Quercus, A cer. (3)Edwardsiana a ln ic o la A lnus, A cer. (3)Edwardsiana a v e lla n a e H azel, elm , sycamore & h o r se -

ch estn u t. (3)Edwards iana p le b e ja (Xiercus, A ln u s, B e tu la , Ulmus(T i l i a & Corylus ? ) . (3)

Bmpoasca d ec ip ien s Lower p la n ts , e sp . U rtica some­tim es t r e e s . (3)

Bmpoasca v i t i s T rees & bu sh es. (3)Eupteryx aurata N e t t le , la b ia t e s , cow parsnip,

burdock, hempagrimony, p o ta to & o th e r s . (3)

Eurhadina concinna Quercus Fagus, B e tu la , Notho-fa g u s, A lnus. (3)

238

Insect species Host plant Ref.

Eurhadina p u lc h e lla Kybos b e tu lic o la Lindbergina a u r o v it ta taLinnavuoriana decempunctata Zygina flammigeraZ ygin id ia s c u t e l i a r i s

Oak.B etu la spp.Quercus, Rubus, Fagus, A lnus, C orylus, B e tu la , C arpinus. B etu la , c o n ife r s & g o r se . Oaks, hawthorn & Prunus s p p ., c o n ife r s , h o lly & iv y .Grass e sp . D. g lom erata , Festuca rubra.H olcus.

(3)(3)(3)(3)(3)(3)(5)

Hemiptera: Homoptera - DelphacidaeC ix iu s nervosus Concmelus anceps

Criomorphus albom arginatus Delphacodes b rev ip en n is Delphacodes fa ir m a ir e i D icran otrop is hamata

H yledelphax e le g a n tu lu s

J a v e s e l la dubia J a v e s e l la p e llu c id a

P ara lib u rn ia d a le i Stenocranus m inutus

Hemiptera: Homoptera - CercopidaeAphrophora a ln i C ercopis v u ln era ta Neophilaenus l in e a tu s

? t r e e s . (7) F o lifer o u s tr e e s & bushes. (6) Juncus. (7) Juncus. (6) Juncus e f f u s u s . (5) G rasses. (4) Damp p la c e s . (7) Damp p la c e s . (7) G rasses. 97) O ats, w heat, Phleum, Des-champsia, A g r o stis c a p i l l a r i s ,H. la n a tu s , E ly tr ig ia rep en s, Arrhenatherum e l a t i u s ,Alopecurus p r a te n s is , Lolium perenne. (6)Holcus spp . (5)G rasses. (7)Deschampsia flex u o sa on m oors, wood g la d es w ith Vaccinium.Festuca rubra. (5)G rasses. (7)G rasses. (7)C erea ls , Avena s a t iv a , Lolium perenne. (6)G rass. (7)A g ro stis c a p i l l a r i s . (5)G rasses. (7)D a c ty lis g lom erata . (6)D a c ty lis g lom erata . (5)

Trees & b u sh es. (4)7 (4)G rasses. (4)Holcus s p p ., D a c ty lisg lom erata. (5)Wide v a r ie ty o f t r e e s & lowp la n ts . (4)Holcus s p p ., D. glom erata. (5)

Philaenus spumarius

239

C oleoptera: C urculionoideaInsect species Host plant R e f .

Amalus sc o r t i l iu m Polygonum a v ic u la r e , Rumexa c e to sa , R. o b t u s if o l iu s . ( 9 )Apion a e th io p s V ic ia c ra cca , V. s a t iv a , V.sepium, V ic ia . ( 9 )Apion ap rican s T rifo liu m p ra ten se . ( 9 )Apion a s s im ile T. hybridum, T. p ra ten se ,T rifo liu m . ( 9 )Apion carduorum Cirsium a rv en se , C. p a lu s tr e ,Cirsium . ( 9 )Apion craccae V ic ia cra cca , V. h ir su ta , V.s a t iv a , V. sepium , V ic ia . ( 9 )Apion c u r t ir o s tr e Rumex a c e t o s e l la , R. a c e to sa , R. c r isp u s , R. o b t u s i f o l iu s ,Rumex. ( 9 )

Apion dichroum T. hybridum, T. p ra ten se , T.rep en s, T r ifo liu m . ( 9 )

Apion hookeri M atricaria , T. maritimum. ( 9 )Apion h yd rolap ath i Rumex c r is p u s , R. o b t u s i f o l iu s ,Rumex. ( 9 )Apion l o t i Lotus c o m ic u la tu s . ( 9 )

Apion marchicum Rumex a c e t o s e l la , Rumex. ( 9 )Apion m e l i l o t i M elilo tu s a lb a , M. a l t i s s im a ,

M. o f f i c i n a l i s , M elilo tu s . ( 9 )Apion miniatum Rumex c r is p u s , R. o b t u s i f o l iu s ,

Rumex. ( 9 )Apion n ig r ita r s e T rifo liu m spp . (1 0 )Apion onopordi Centaurea s p p ., Arctium lap p a ,

Carduus n u ta n s, Onopordumacanthium, Cnicus b en ed ic tu s . (1 0 )

Apion pubescens T rifo liu m cam pestre, T. dubium,T rifo liu m . (9 )

Apion rubens Rumex a c e t o s e l la , Rumex. ( 9 )Apion sanguineum Rumex a c e t o s e l la . ( 9 )Apion s im ile B etu la pendula , B etu la . (9 )Apion tenue Medicago, T. p ra ten se ,

T rifo liu m . ( 9 )Apion t r i f o l i i T. p ra ten se . (9 )Apion v ire n s T. p ra ten se , T. repens,

T rifo liu m . (9 )Ceuthorrhynchus a s s im il i s Raphanus raphanistrum ,

C ru ciferae . (9 )Ceuthorrhynchus con tractu s Raphanus, C a p se lla . (9 )Ceuthorrhynchus erysim i C ru c ifera e , C a p se lla bursa-

p a s t o r is . (9 )Ceuthorrhynchus f l o r a l i s C ap se lla b u r s a -p a s to r is ,

C a p se lla , C ru c ifera e . (9 )Ceuthorrhynchus l i tu r a Carduus a r v e n s is . (1 0 )Ceuthorrhynchus m o lle r i H ieracium , Leontodon. (9 )Ceuthorrhynchus m arginatus Taraxacum o f f i c i n a l e , Hypo-

c h a er is m acu lata , Crepisv ir e n s , Lactuca s e r r io la . (9 )

Ceuthorrhynchus pyrrhorhynchus Sisymbrium o f f i c in a le . (9 )

2 4 0

Insect species Host plant Ref.

Ceuthorrhynchus quadridens Raphanus raphanistrum ,C ru c ifera e. (9 )

Ceuthorrhynchus rugu losu s M a tr ica r ia , T. maritimum. (9 )Deporaus b etu la e B etu la pendula , B. p u b escen s,

B e tu la , Fagus s y lv a t ic a . (9 )Gronops lu n atu s Spergula a r v e n s is , T. inodorum. (9 )Gymnetron pascuorum Plantago la n c e o la ta , P la n tag o . (9 )Hypera arator Spergula a r v e n s is , S t e l la r ia

m edia. (9 )Hypera n ig r ir o s t r is T. hybridum, T. p ra ten se , T .

rep en s, T r ifo liu m . (9 )Hypera p e d e s tr is L otus. (1 0 )Hypera p la n ta g in is Lotus u l ig in o s u s , Plantago

la n c e o la ta , P lantago m ajor,P la n tag o , T. p ra ten se , T. rep en s. (9 )

Hypera p o s t ic a Lotus c o r n ic u la tu s , Medicagolu p i l in a , M edicago, T. hybridum,T. p r a te n se , T. rep en s,T r ifo liu m , V ic ia s a t iv a , V ic ia sepium , Leguminosae. (9 )

M iccotrogus p ic i r o s t r i s T. hybridum, T . p ra te n se . (9 )Otiorrhynchus s in g u la r is B etu la , Fagus s y lv a t ic a , p o ly -

phagous. (9 )P h y llob iu s argen tatu s B etu la , Fagus s y lv a t ic a ,

Q iercu s, Sorbus aucuparia. (9 )Polydrosus cerv in u s B etu la pen d u la , B etu la ,

D a c ty lis g lcm era ta , CMercus,Graminae, Polyphagous. (9 )

P h y llob iu s m a cu licorn is B etu la , Q oercus. (9 )P h y llob iu s p y r i B e tu la , Sorbus. (9 )P h y llob iu s quadr itu b er c u la tu s Polygonum a v ic u la r e , Polygonum

p e r s ic a r ia . (9 )P h y llob iu s u r t ic a e N e t t le s . (10)P h y llob iu s v ir id e a r is Populus trem u la , S a lix ca p rea ,

S a lix v im in a l i s , Ulittus ca m p estr is . (9 )

Rhinoncus bruchoides Polygonum p e r s ic a r ia , Poly­gonum. (9 )

Rhinoncus c a sto r Polygonum a v ic u la r e , R.a c e t o s e l la , Polygonum, Rumex. (9 )

Rhinoncus p erp en d icu la r is Polygonum. (9 )Rhamphus p u lic a r iu s B etu la pendula , B etu la

p u b escen s, B e tu la . (9 )Rhynchaenus fa g i Fagus s y lv a t ic a . (9 )Rhynchaenus r u s c i B etu la pendula, B. p u b escen s,

B etu la , Q iercu s. (9 )S iton a h isp id u lu s Lotus u lig n o s u s , M. lu p i l in a ,

Medicago, T. p ra ten se , T. rep en s, T r ifo liu m . (9 )

S iton a hum eralis L otus, M. lu p i l in a , M edicago,T. hybridum, T. p ra te n se , T. rep en s, T r ifo liu m , V ic ia . (9)

VD

CX

I-ja

^Ul^

UJN

Jl—*

241

Insect species Sitona lepidus

S iton a l in e a tu sS iton a r e q e n ste in e n s is S iton a s u lc ifr o n sStrophosanus melanogrammus

Tychius p u s i l lu sC oleoptera: Chryscm elidae

Bruchus c i s t i Bruchus l o t i Bruchus p i s i Bruchus r u f ip e sC assida f la v e o laC assida ru b ig in osaC assida v i t t a t aChaetocnema concinna

Chaetocnema h o r te n s is Crepidodera ferru g in eaCrepidodera tra n sv ersaGastrophysa p o lygon iH ippuriphila modeeri P h y llo tr e ta nemorum Phytodecta o l iv a c e a

References

= Southwood & L eston , (1959) = Hodkinson & White (1979)= Le Quesne & Payne (1981)= Le Quesne (1965)= W aloff & Solomon (1973)= O ssia n n ilsso n (1983)= Le Quesne (1960)= Le Quesne (1969)= Hyman (1983)

10 = Joy (1932)

Host plant Ref.

Lotus u lig n o s u s , Medicago lu p i l in a , T. p ra te n se ,T rifo liu m , Leguminosae. (9 )L otus, M edicago, T. p r a te n se , T rifo liu m , V ic ia . (9 )C ytisus sc o p a r iu s . (9 )Lotus c o r n ic u la tu s , T. p ra ten se , T r ifo liu m , V ic ia . (9 )Deschampsia f le x u o s a , Fagus s y lv a t ic a , Quercus robur,Quercus, Polyphagous. (9 )Lotus c o m ic u la tu s , T r ifo liu m . (10)

Lotus c o m ic u la t u s . (9 )V ic ia c ra c c a , V ic ia s a t iv a ,V ic ia . (9 )S t e l la r ia gram inae, S t e l la r ia h o ste a . (9 )Cirsium a rv en se , Cirsium v u lg a re , C irsium . (9 )Spergula a r v e n s is , U rtica d io ic a , U r t ic a . (9 )Chenopodium, Polygonum a v ic u la r e , Polygonum, Rumex o b t u s i f o l iu s . (9 )G rasses. (9 )Cirsium , U r tica d io ic a , U r t ic a , Ccmpositae, Graminae. (9 )Cirsium , U r t ic a , U r tic a ,Compositae, Graminae. (9)Polygonum a v ic u la r e , Polygonum,Rumex. (9 )Equisetum a rv en se . (10)C ru ciferae. (9 )C ytisus sc o p a r iu s . (10)

24 Z

AFPEND IX 2

a) WINT'S METHQO FOR TANNIN ESTIMATION

The quantitative estimation of the nutritive Inhibitor content of experimental

host plant leaves : the enzyme assay reagent and procedures.

The basic starch-amylase reaction

1) REAGENTS USED

a) Stock start reagent mixture

50ml. Soluble starch solution (Igm.in 500ml water)

20ml. Salt (NaCI) solution (1% w/w)

20ml. Phosphate buffer, for ph b.b.

The buffer solution was made up from two solutions, in the ratio of 3:2

i.e. 150ml. solution 1 and 100ml of solution 2.

Solution 1 - 2.269g.KHeFD* in 250ml water.

Solution 2 - 4.75g IMasHPO .. 12HB0 in 250ml water.

b) Enzyme Solution

An aqueous solution of a-amylase (type 111 —A, from Bacillus subtil is

obtainable from Sigma London Chemical Company Ltd.) was prepared at 0.4-

mg/ml, 0.3 mg/ml, 0.2 mg/ml and 0.1 mg/ml.

c) Iodine indicator solution

5ml. Ia in 5% KI

245ml water

d) Tannic Acid Solutions

1g tannic acid in 1 litre Hs0 dilute down to 0.1, 0.05, 0.025 and 0.0067*

solutions.

243

2. STANDARD REACTION PROCEDURE

4.5ml of the starch reagent mixture was added to 1ml of each of the four

enzyme solutions, held in a water bath at 20 *C. Every 15 seconds, 0.25ml.

of each reacting mixture was withdrawn and added to 4ml. of the iodine

indicator solution until the end point was reached, as indicated when no

change in the colour of the iodine solution was produced by the action of

the enzyme-starch. The endpoint was determined by eye in natural daylight

against a white background.

THE ASSAY

1Q0mg of powdered leaf material was added to 2ml.Ha0. The samples were placed

on a mechanical shaker for 1 hour. These were centrifuged at 5000 rpm for 10

minutes and the supernatant was retained.

0.25ml of the supernatant was added to 1ml. of each of the enzyme solutions.

These were left for 10 minutes exactly to complex. 4.5ml. of the starch reagent

mixture was then added to each enzyme mixture, and the resultant endpoints

determined as described above.

In order to standardise the method 0.25ml. of each of the tannic acid

solutions was substituted for leaf extract and the reaction carried out as

before.

A control assay was performed alongside the experimental assays, in which

water was substituted for the leaf-extract. The end points for this test were

then subtracted from those of the leaf extract assays to give the delays in

the end point of each enzyme-starch reaction.

The delay in seconds at each enzyme concentration was then plotted against

tannic acid concentration and used as calibration curves. The equivalent tannic

acid concentrations to those found in the leaves were then read o ff the graph.

2 4 ^ r

b> KJELDAHL DETERMINATION OF NITROGEN HVI L EAVES

Total Nitrogen

1) 60mg of dried material was placed into a Kjeldahl flask.

H) 2mls. of cone, sulphuric acid (Nitrogen-free) were added to the flask.

3) A single selenium catalyst tablet was added to the flask.

4) The flasks were placed in a Kjeldahl burner. Initially they were heated

gently; the heat was increased when dense white fumes were no longer

emitted.

5) The tubes were heated until the digestion was complete, that is when the

solution was clear lemon yellow and stayed that way even when shaken.

The flasks were allowed to cool. The solution was then made up to 50mIs.

with distilled water.

6) A flask with no leaf material added was treated in the same way and

served as a blank.

7) 2ml. of the solution was placed in tubes and passed through a Technicon

Auto Analyser.

8) 4 standard solutions of nitrogen were made up to concentrations o f 1, 5,

10 and 20ppm. 2ml. of each of these were also passed through the Auto

Analyser.

9) The peak height of each standard solution was measured on the print out.

A calibration curve was drawn on log graph paper. The nitrogen

concentration of each sample was read off the calibration curve after

calculating peak height.

245

A F F E N D I X ^

Regression analysis of absolute abundance for each insect group in order

determine the distribution of the

PARAMETER

data.

ESTIMATE S.E T. VALUE P

Cicadellidae

Intercept -0.2992 0.3083 0.9704 0.3372

Slope 1.4573 0.0947 15.3744 <0.001

Delphacidae

Intercept 6.0817x10--B 0.2056 0.3 0.7697

Slope 1.2133 0.1401 8.66 <0.001

Curculionoidea

Intercept 2.3857 1.6666 1.43 0.1591

Slope 1.3001 0.0966 13.46 <0.001

Heteroptera

Intercept -2.5065 0.5673 4.42 <0.001

Slope 3.5509 0.0144 246.4 <0.001