biodiversity and functional role of spiders (araneae) …
TRANSCRIPT
BIODIVERSITY AND FUNCTIONAL ROLE OF
SPIDERS (ARANEAE) IN WHEAT AGRO-
ECOSYSTEM OF PUNJAB, PAKISTAN
By
SHER MUHAMMAD SHERAWAT
DEPARTMENT OF ZOOLOGY
UNIVERSITY OF THE PUNJAB
LAHORE, PAKISTAN
(2012)
BIODIVERSITY AND FUNCTIONAL ROLE OF
SPIDERS (ARANEAE) IN WHEAT AGRO-
ECOSYSTEM OF PUNJAB, PAKISTAN
By
SHER MUHAMMAD SHERAWAT
A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF
Doctor of Philosophy
In the Faculty of the Life Sciences, University of the Punjab, Lahore, Pakistan
Supervisor
DR. ABIDA BUTT
Department of Zoology University of the Punjab, Quaid-e-Azam Campus
Lahore, Pakistan (2012)
CERTIFICATE
This is to certify that the research work described in this thesis is the original
work of the author and has been carried out under my direct supervision. I have
personally gone through all data/results/materials reported in the manusript and certify
their correctness and authenticity. I further certify that materials included in this thesis
have not been used in part or full in a manuscript already submitted or in the process of
submission in partial/complete fulfillment for the award of any other degree from any
other institution. I also certify that the thesis has been prepared under my supervision
according to prescribed format and I endorse its evaluation for the award of Ph.D degree
through the official procedures of the University.
DR. ABIDA BUTT
(Research Supervisor)
Signature: _______________
Stamp: _______________
i
Summary
A study was conducted to assess the effects of local landscape heterogeneity and
agronomic practices on dynamics of spiders residing wheat fields of traditional “Kalar
tract”of Punjab, Pakistan. For this purpose two sites at Adaptive Research Farm,
Sheikhupua(31°43’N, 73°59’E, 209 m elevation from sea) and Adaptive Research Farm,
Farooqabad of Punjab, Pakistan were selected.At each site, five wheat fields(1 to
5)varying in terms of inputs,cultivation and surrounding crops were chosen randomly.
Field 1, surrounded by brassica (BW), field 2, surrounded by Trifolium(TW) and field 3,
surrounded by other wheat fields(WW).Wheat was sown in these three fields by
conventional way but they differ in surrounding crops.In field 4 wheat was sown after
harvesting of rice crop without tillage (ZW) and surrounded by conventional wheat. Field
5 was wheat plot without input of chemical fertilizers (LW) and surrounded by
conventional wheat plots. Specimens were collected from both the sites using pitfall traps
and visual observations during wheat crop period of 2007-2009.During the study, 23097
spider specimens belonging to 47 species, 31 genera and 12 families were sampled from
wheat fields of five different areas. Of the total sample, 37 % individuals were juvenile,
32 % adult males and 31 % adult females. The three most abundant families were
Lycosidae, Tetragnathidae and Oxyopidae which collectively contributed 75.93% of the
total catch.The most abundant species of overall data were Lycosa terrestris (34.18%),
Pardosa birmanica (16.64%), Tetragnatha javana (10.56%), Neoscona theisi (6.31%),
Oxyopes javanus (7.84%), unidentified species of Erigone genus (7.0%), Bianor
albobimaculatus (1.26%), Hassarius adansoni (1.33%) and Leucage decorata
(2.07%).The collective contribution of these species was 87.12%. However, abundance of
these species varies in foliage and pitfall samples. The total species richness was 47.44
and 48.9 on the basis of Chao 2 and Jacknife 2 estimates, respectively. The ratio of
observed to estimated number of species was 96% whichsuggested that at least 4% more
species were present in the area than actually collected.
The activity / density (number captured per trap)and richness were similar in both
study sites and study years.Abundance and richness of spider varied in all plots.Whereas,
diversity and evenness was not different in these fields. Richness and abundance differed
significantly during different trapping sessions. Guild composition among five fields was
similar statistically. Significant positive correlation was observed between active density
ii
of ground spiders and collembolans population during different trapping session of all
studiedplots except low input plots.
In other study the effects of Brassica strip cropping (intercropping) in wheat crop
on the population of aphids and its predators were studied. For this purpose study fields
were selected in district Sheikhupura, Pakistan during cropping session 2006-07 and
2007-08 at three different sites.In each field, Brassica strips of four different sizes were
grown in the centre of field. In treatment 1 (T1) width was 0.6m, treatment2 (T2) 1.21m,
treatment3 (T3)1.82m and treatment 4 (T4) 3.65m.In control field no intercropping was
present. During the study significant difference in number of aphids per tiller was
observed among treatments. Highest number of aphids per tiller was recorded in control
wheat plot, while lowest in the plot (T4). Highest number of Coccinellids, Chrysoperla
carnea and Araneae (spiders) was recorded in T4 while lowest in control. Maximum
1000-grain weight was recorded in T4 treatment (42.80g) while minimum in control
treatment (36.57g). However, T3 treatment showed highest yield (5468kg/ha) followed
by T2. The treatment T3 showed highest cost benefit ratio value (1:1.95) while lowest
cost benefit ratio (1:1.77) was observed in T4. It is concluded that strip cropping of
Brassica napus in wheat fields increases predators population which suppress the aphids
population and enhances the yield.
Experiments were conducted to study the effect of modular habitat refugia on the
density and diversity of most dominant spider species. Modular habitat refugia was made
up of mulberry twig baskets filled with chopped paddy straw and dried leaves of
Dalbergia sisso to provide shelter to natural predator populations. Refugia fields held
more density of spiders, rove beetls and coccinellids as compared to control plots.
However, the number of spiders species did not vary in the control and refugia plots.
Decrease in the abundance of aphids was also noted in refugia plots as compared to
control plots. The results showed that habitat refugia either in the form of strip crops or
dried leaves may be used to enhance the abundance of arthropod predators and to
suppress pest population in agro-ecosystem.
To assess the predatory efficacy of spiders against insect pests of wheat crop three
most dominant hunting spiders (viz., Lycosa terrestris, Pardosa birmanica and Oxyopes
javanus), were selected. For laboratory evaluation, both choice and no choice feeding
experiments were performed using three insect pest species, Mythimna separata (Oriental
armyworm),Sesamia inferens (pink graminous stem borer) and Sitobion avenae (aphid).
iii
Labortory experiments showed that spiders consumed all the prey items offered but in
different proportions. Killing rate of aphid (nymph and adult) was higher than other prey
types. Oxyopes javanus was more voracious predator as compared to Lycosa terrestris
and Pardosa birmanica. Females consumed higher number of prey than males in both
choice and no choice feeding tests. In field, seasonal variation was recorded in diet of
each species. However, monthly diet composition of the three studied species did not
differ from each other. Field observations also showed that aphid is a major part of spider
food. On the basis of this study, it is concluded that spiders can be used as biological
control agent in the field to suppress apid population.
The susceptibility of dominantspiders species against pesticides was also
recorded. Spiders exposed to insecticides confidor showed high susceptibility with
increased concentration and exposure time. In L. terrestris at simulated field rate, 75
percent mortality was recorded after 24 hours.However, in O. javanus only 65 percent
mortality was recorded for the same concentration and the dose. Confidor was highly
toxic to both agrobiont species of spiders. The comparison of the susceptibility of two
species against confidor did not show any significant difference from each other. Both
spider species did not show susceptibility against herbicide Buctril-M used in the
experiment.The mortality of both spider species declined with the increase of post spray
time. The residues of confidor degraded rapidly in the lab experiment. Approximately
within 3 days, the susceptibility of this insecticide decreased more than 50 %. The
residual toxicity of Buctril-M was low and did not vary for both spider species.
In the field, abundance of L. terrestris and O. javanus was negatively associated
with the insecticide spray.Results showed that in each trapping session the number of
wolf spider varies in treated and control plots just after the application of insecticides
Confidor. However, the densities of both species start to re-establish after few days of
spray. The herbicide treatment did not affect the density of both dominant species even in
the field.
The results of this study showed that conservation of spiders in the wheat
fields can be helpful to supress its pest population. However, integration of
different techniques to suppress pest population requires detail studies. Many other types
of refugia can be used to enhance the predator populations in the field. Alongwith that
further studies require to choose the proper pesticide in the field.
iv
Dedication
Dedicatedtomyfamily members and late mother
v
Acknowledgements
First of all I thank to Almighty Allah, the compassionate and merciful, who
enabled me to complete this project. I am thankful to Department of Zoology, University
of the Punjab for providing me research facilities. I owe special thanks to my respectable
research supervisor Dr. Abida Butt for her enthusiastic encouragement, cooperation, kind
behavior and valuable guidance throughout the completion of this project. I am also
thankful to Hafiz Muhammad Tahir, Imtiaz Alam and Muhammad Adnan Ali for giving
me valuable suggestions to improve the manuscript. I am grateful to Dr. Azhar Mahmood,
Mr. Abid Mahmood Shirazi and Muhammad Akram for their help to compile this
manuscript. My special thanks are to my colleagues, research mates, Laboratory staff and
family members who constantly inspired me to maintain my interest toward this project.
SherMuhammadSherawat
vi
List of Abbreviations
Acronym Meaning
LC50 Lethal concentration
LT50 Lethal time
RIF Reduce input field
ORG Organic field
TLF Tilled field
HTF Herbicide treated field
CCA Canonical correspondence analysis
CoA Correspondence analysis
FR Field application rate
ANOVA Analysis of variance
CBR Cost benefit ratio
IPM Integratedpest management
MVSP Multivariate statistical package
vii
Contents
Summary _____________________________________________________________________________ i
Dedication __________________________________________________________________________ iv
Acknowledgements _____________________________________________________________________ v
List of Abbreviations __________________________________________________________________ vi
Contents ____________________________________________________________________________ vii
List of Tables _________________________________________________________________________ x
List of Figures _______________________________________________________________________ xi
List of Appendices ___________________________________________________________________ xiii
Chapter 1 ____________________________________________________________________________ 1
1. GENERAL INTRODUCTION _____________________________________________ 1
Chapter 2 ____________________________________________________________________________ 5
2. REVIEW OF LITERATURE _______________________________________________ 5
Chapter 3 ___________________________________________________________________________ 11
3. EFFECT OF DIFFERENT AGRICULTURAL PRACTICES ON SPIDERS AND THEIR PREY
POPULATIONS IN SMALL WHEAT FIELDS ____________________________________ 11
3.1 Introduction _______________________________________________________________ 11
3.2 Materials and Methods ______________________________________________________ 12
3.2.1 Study Area ___________________________________________________________________ 12
3.2.2 Sampling ____________________________________________________________________ 13
3.2.3 Data Analyses ________________________________________________________________ 14
3.3 Results ____________________________________________________________________ 15
3.3.1 Spider Assemblages____________________________________________________________ 15
3.4 Discussion _________________________________________________________________ 26
Chapter 4 ___________________________________________________________________________ 30
4. EFFECT OF BRASSICA STRIPS ON THE POPULATION OF APHIDS AND ARTHROPOD
PREDATORS IN WHEAT ECOSYSTEM _______________________________________ 30
viii
4.1 Introduction _______________________________________________________________ 30
4.2 Materials and Methods ______________________________________________________ 31
4.2.1 Collection of Specimens ________________________________________________________ 32
4.2.2 Yield Assessment ______________________________________________________________ 33
4.2.3 Data Analyses ________________________________________________________________ 33
4.3 Results ____________________________________________________________________ 33
4.4 Discussion _________________________________________________________________ 41
Chapter 5 ___________________________________________________________________________ 43
5. EFFECT OF STRAW REFUGIA ON THE ACTIVITY DENSITY OF ARTHROPODS
PREDATORS AND APHIDS IN THE WHEAT ECOSYSTEM ________________________ 43
5.1 Introduction _______________________________________________________________ 43
5.2 Materials and Methods ______________________________________________________ 45
5.2.1 Statistical Analyses ____________________________________________________________ 47
5.3 Results ____________________________________________________________________ 47
5.4 Discussion _________________________________________________________________ 59
Chapter 6 ___________________________________________________________________________ 63
6. PREDATION OF SPIDERS ON INSECT PESTS OF WHEAT CROP ________________ 63
6.1 Introduction _______________________________________________________________ 63
6.2 Materials and Methods ______________________________________________________ 65
6.2.1 No‐choice Feeding Tests ________________________________________________________ 65
6.2.2 Choice Feeding Tests ___________________________________________________________ 65
6.2.3 Fields Observations for the Predators _____________________________________________ 66
6.2.4 Statistical Analyses ____________________________________________________________ 66
6.3 Results ____________________________________________________________________ 66
6.3.1 Non‐ Choice Feeding Test in Laboratory ____________________________________________ 66
6.3.2 Choice Feeding Test in Laboratory ________________________________________________ 67
6.3.3 Field Observations _____________________________________________________________ 67
6.4 Discussion _________________________________________________________________ 74
ix
Chapter 7 ___________________________________________________________________________ 77
7. EFFECTS OF PESTICIDES ON AGROBIONT SPIDERS IN LABORATORY AND FIELD __ 77
7.1 Introduction _______________________________________________________________ 77
7.2 Materials and Methods ______________________________________________________ 79
7.2.1 Pesticides ____________________________________________________________________ 79
7.2.2 Test Organisms _______________________________________________________________ 79
7.2.3 Topical Exposure ______________________________________________________________ 79
7.2.4 Residual Toxicity ______________________________________________________________ 80
7.2.5 Field Assays __________________________________________________________________ 80
7.2.6 Statistical Analyses ____________________________________________________________ 81
7.3 Results ____________________________________________________________________ 81
7.3.1 Topical Exposure ______________________________________________________________ 81
7.3.2 Residual Toxicity ______________________________________________________________ 82
7.3.3 Field Assay ___________________________________________________________________ 91
7.4 Discussion _________________________________________________________________ 91
Chapter 8 ___________________________________________________________________________ 94
GENERAL DISCUSSION __________________________________________________ 94
Chapter 9 __________________________________________________________________________ 100
REFERENCES _________________________________________________________ 100
x
List of Tables
Table 3.1: Abundance of spiders collected from wheat fields during study period _________________ 17
Table 3.2: Species richness estimates and inventory completeness for each habitat type ____________ 20
Table 3.3: Difference among habitat types for active density of agrobiont species. ________________ 23
Table 4.1: Weight of 1000 grains and yield in various treatments of Brassica napus in wheat
field _____________________________________________________________________ 39
Table 4.2: Economic analysis of different treatment of Brassica napus on yield of wheat crop _______ 40
Table 5.1: Total abundance of each spider species recorded from different areas _________________ 49
Table 6.1: Mean number of prey killed by different sexes of hunting spiders after 24 h of
exposure in no choice feeding experiment _______________________________________ 68
Table 6.2: Mean number of prey killed by different sexes of three hunting spiders at 24 h of
introduction in choice feeding experiment _______________________________________ 69
Table 6.3: Average consumption or killing (%) of various insect orders by three hunting spiders
in the wheat fields during a season. ____________________________________________ 72
Table 6.4: Body measurements of wheat insect pests and three hunting spiders used in the
experiment ________________________________________________________________ 73
Table 7.1: LC50 of confidor and butril-M for the agrobiont spider species _______________________ 84
Table 7.2: LT50 of confidor and butril-M for spider species ___________________________________ 85
xi
List of Figures
Figure 3.1: Species accumulation curves for the five different habitats of wheat field (BW, mix
cropping of brassica and wheat;TW, mixing cropping of trifolium and wheat;ZW,
wheat sown without tillage;WW, monoculture wheat;LW, low input wheat. ____________ 19
Figure 3.2: Dendrogram for species shared at different habitats types using the unweighted pair
group average(UPGMA) and Euclidean distance.Habitats types are coded by BW,
mix cropping of brassica and wheat;TW, mixing cropping of trifolium and wheat;ZW,
wheat sown without tillage; WW, monoculture whea ;LW, low input wheat _____________ 21
Figure 3.3: Temporal change in abundance of aphid population in five different habitats of wheat
fields (combined for both sites and years). BW, mix cropping of brassica and
wheat;TW, mixing cropping of trifolium and wheat;ZW, wheat sown without
tillage;WW, monoculture wheat;LW, low input wheat. ______________________________ 24
Figure 3.4: Seasonal dynamics of collembolan’s population (combined for two years) in five
different habitats of wheat fields (combined for both sites and years). BW, mix
cropping of brassica and wheat;TW, mixing cropping of trifolium and wheat;ZW,
wheat sown without tillage;WW, monoculture wheat;LW, low input wheat. _____________ 25
Figure 4.1: Population of lady bird beetles among different treatment and sites ___________________ 35
Figure 4.2: Population of aphids among different treatment and sites ___________________________ 36
Figure 4.3: Population of Chrysoperla carnea among different treatment and sites ________________ 37
Figure 4.4: Population of spiders among different treatment and sites ___________________________ 38
Figure 5.1: Variation in the abundance of spiders in refugia and control plots ____________________ 51
Figure 5.2: Variation in the number of coccinellids in refugia and control plots. __________________ 52
Figure 5.3: Variation in the number of rove beetles in refugia and control plots ___________________ 53
Figure 5.4: Variation in the number of aphids in refugia and control plots _______________________ 54
Figure 5.5: Abundance of spiders at different distances from edge to centre of field ________________ 56
Figure 5.6: Abundance of rove beetles at different distances from edge to centre of field ____________ 57
Figure 5.7: Abundance of coccinellids at different distances from edge to centre of field ____________ 58
Figure 6.1: Variation in number of killed prey items during no- choice and choice feeding
experiments. A: Lycosa terrestris, B: Pardosa birmanica and C: Oxyopes javanus _______ 70
Figure 6.2: Seasonal change in the diet composition of hunting spiders. A:Lycosa terrestris,
B:Pardosa birmanica and C:Oxyopes javanus ____________________________________ 71
Figure 7.1: Response of spiders to different concentrations of pesticides exposed. ■ represent
mortality of L. terretris and □ O. javanus to cofidor. Mortality due to Buctril- M was
represented by ▲in L. terretris and ∆in O. javanus. (FR = Field application rate) _______ 83
xii
Figure 7.2: Laboratory Response of L. terrestris (A) and O. javanus (B) against confidor
residues of different age. __________________________________________________ 85‐87
Figure 7.3: Laboratory Response of L. terrestris (A) and O. javanus (B) against Buctril‐M residues
of different age ____________________________________________________________ 88
Figure 7.4: Effect of pesticide on the abundance of L. terrestris after the treatment of crop field.
Arrow of December represents spray of buctril‐M and March of confidor _______________ 89
Figure 7.5: Effect of pesticide on the abundance of O. javanus after the treatment of crop field.
Ist arrow represent spray of buctril-M and 2nd arrow of confidor ____________________ 90
xiii
List of Appendices
1. Butt, A., Sherawat, S.M., 2011. Effect of different agricultural practices on spiders
and their prey populations in small wheat fields. Acta Agriculturae Scandinavica
Section B _ Soil and Plant Science 2011, 1- 9.
2. Sherawat, S.M., Butt, A., and Tahir, H. M., 2012. Effect of Brassica strips on the
population of aphids and arthropod predators in wheat ecosystem. Pakistan J. Zool.,
vol. 44 (1), pp. 173-179.
1
Chapter 1
1. GENERALINTRODUCTION
Agriculture is considered the lifeblood of Pakistan’s economy and wheat (Triticum
aestivumL.) is the largest grain crop of the country. It contributes 13.1 percent to the
value added in agriculture and 2.7 percent to GDP. Wheat was cultivated on an area of
8805 thousand hectares with total production of 24.2 million tons (Govt. of Pak., 2011).
Being staple food, average per capita consumption of wheat is 140kg in Pakistan (Mann
et al., 2008). Wheat is the cheapest source of feed for livestock and poultry in the country.
Its straw is mainly used as feed for cattle and for silage preparation.
The irrigated areas of Punjab mainly consist of three agro ecological zones; Wheat-
rice, wheat-cotton and central mixed crop area of the Indus basin. Wheat-rice, wheat-
cotton and wheat-fodder are the three major crop rotations of these zones, respectively
(Ibrahim et al., 2008). The world famous aromatic Basmati varieties of rice are grown in
the wheat-rice zone commonly known as "Kalar tract"(salt affected land) which mainly
lies in our study area of district Sheikhupura.
In Pakistan, average grain yield of wheat is 2639 kg per hectare which is very low as
compared to other countries like Indiaand Chinai.e., 2802 and 4762 kg per hectare,
respectively. The traditional methods of cultivation, low yielding varieties, fragmented
holdings, illiteracy, lack of irrigation water, relatively low level of soil fertility and higher
incidence of insect pests and diseases are considered to be responsible factors for low
yield.A wide range of insect pests like aphids, termites, armyworm and pink graminous
stem borers infest wheat crop but aphids are considered as the most destructive pests
(Aheer et al., 2006; Khattak et al., 2007). Aphids cause 16.4 % grain yield loss, either
through direct feeding or as virus vector (Aheer et al., 1993). The honeydew exuded by
aphids also encourages the snappy growth of sooty fungus on foliage, which eventually
affects the rate of photosynthesis in wheat plants (Mahmood, 1981). Although aphid is
considered major pest of wheat but its population seldom crosses the economic threshold
level each year. It is apprehended that in Pakistan aphid may becomes a regular pest in
2
the ensuing years due to favorable conditions i.e., excessive use of nitrogenous fertilizers
and susceptible varieties (Wains et al., 2010).
The insect pests can be controlled naturally by the arthropods predators.
Suppression of insect pest population through natural predators like spiders, lacewings
and coccinellids is the prime objective of the modern biological control. These predators
are commonly present in our agroecosystems and regulate the population of insect pests.
However, their abundance in agroecosystems is affected by the agricultural practices.
These can be conserved through habitat manipulation and making the existing agricultural
practices favourable to the spiders (Landis et al., 2005). Spiders mainly feed on insects
and form one of the most ubiquitous groups of predacious organisms in animal kingdom
(Marc et al., 1999; Symondson et al., 2002). According to Gavish-Regev et al. (2009)
spiders caused up to 50% reduction in aphid populations in wheat fields. Spiders are
major predators of aphids in wheat fields (Lang, 2003; Öberg et al., 2008; Oelbermann et
al., 2009).
The agricultural intensification is characterized by higher use of pesticide and
fertilizer inputs, tillage operations, increasing simplification of agricultural landscapes
and loss of biodiversity (Foley et al., 2005; Tscharntke et al., 2005; Billeter et al.,
2008).Theagronomic practices such as ploughing, zero tillage, low and high inputs,
irrigation, harvesting, surrounding habitats and intercropping affect the diversity and
abundance of spiders. Diversity of spiders in agro- ecosystems may favour reduced pest
pressure and enhanced activity of natural enemies (Altieri, 1991; Andow, 1991;
Ryszkowski et al., 1993; Stamps and Linit, 1998). The diversity and density of predators
can be increased through habitat manipulation and by improving agricultural practices.
Low-input farming potentially sustains larger and diverse spider communities than
intensive systems because of the absence of agrochemical use and typically more
complex crop rotations within the system (Gluck and Ingrish, 1990; Bengston et al.,
2005).It is also reported that highly fertilized fields support more herbivores, detritivores
and predators as well (Siemann, 1998). Herbicides may reduce population of
phytophagous insects, which results in less available prey for spiders (Amalin, et al.,
2001). Disturbance created by herbicide can decrease the population size for more than a
month after application (Clausen, 1990).
3
Although Punjab Agriculture Department does not recommend the use of
insecticides to control wheat aphids in Pakistan but the pesticides firms are encouraging
the growers to apply insecticides for the control of wheat aphids. The insecticides are
effective against aphids but their indiscriminate use also affects prey-predator
relationship. To prevent the application of pesticides especially in wheat ecosystem and to
suppress the pest population, integrated pest management programme is the dire need of
modern agriculture. Several researchers reported the detrimental effects of insecticides on
the population of insect predators (Richert and Lockley, 1984; Mansour et al., 1992). The
application of pesticides that are comparatively harmless to natural predators may
increase their effectiveness. It further may lead to lower production cost and reduced
environment pollution. Some pesticides are less toxic to predators (Mansour et al., 1981;
Mansour and Nentwig, 1988; Geiger et al., 2010).
The habitat vicinity may function as refuges for spiders and act as a source of
dispersal into arable fields (Öberg and Ekbom, 2006). Refuge habitats are of major
importance for many arthropods populations during times when crops are disturbed
(Landis et al., 2000; Sunderland and Samu, 2000). Refuge habitats may include bush land
patches, field edges, roadside verges, domestic parks or gardens, and planted crops. Most
of the spiders that are typically found in crops emigrate from treated fields and over
winter predominantly in surrounding habitats (Marc et al., 1999; Thomas and Jepson,
1999; Thorbek and Bilde, 2004; Schmidt and Tscharntke, 2005). Species composition of
spiders depends on the surrounding habitats, adjacent crops, management practices in the
agricultural fields (Wissinger, 1997; Raizer and Amaral, 2001) and density of prey in the
field (Moring and Stewart, 1994; Cole et al., 2005).Modular habitat refugia can enhance
predator population by giving shelter (Riechert and Bishop, 1990;Rypstra et al., 1999),
providing alternative prey from the detritivore food chain (Humphreys and Mowat, 1994;
Scheu, 2001) and by reducing intraguild predation (Finke and Denno, 2002).
Promoting heterogeneity in land use at landscape scales is one of important factors
responsible for higher spider diversity in agro ecosystems (Clough et al., 2005).It is also
reported that local factors and spatial surroundings of habitat may have strong impacts on
local diversity, abundance of spiders and biological control (Karevia and Wennergren,
1995; Kruess, 2003; Schmidt et al., 2004; Holland et al., 2004).Intercropping is a form of
habitat manipulation and a potentially befitted technology to reduce pest outbreak and to
increase crop production due to its substantial yield advantage than sole cropping(Ofori
and Stern, 1987; Awal et al., 2006). Similarly the natural and semi-natural habitats
4
around or within agricultural fields can enhance the abundance and species diversity of
spiders, e.g., nearby grasslands (Schmidt and Tscharntke, 2005), field margins (Pfiffner
and Luka, 2000) and weed strips within a field (Collins et al., 2002; Macleod et al.,
2004).
Despite the fact that the spiders have great predatory potential to control the insect
pests but they are not being used by the farmers as a natural biological control agent in
Pakistan due to lack of information. It is imperative to explore the effect of cultural
practices on spiders and predatory potential of spiders so as to increase the predictability
of success before introductions are made. For this purpose, the effect of habitat
manipulation, cropping pattern, adjacent crops and agricultural practices on the diversity
and population dynamics of spiders must be studied. Keeping in view of above facts,
present study was designed. The specific objectives of the present study are as under:
1. To record the diversity and population dynamics of spiders residing in the wheat
fields of traditional “Kalar tract” of Punjab;
2. to study the effects of local landscape heterogeneity and agronomic practices on
population dynamics of agrobiont spiders (most dominant species);
3. to study the effect of different types of refugia on population of agrobiont spiders;
4. to assess the effects of pesticides on survival of agrobiont spiders;
5. to assess the role of spiders in suppression of aphids populations (Lab and field
studies).
5
Chapter 2
2. REVIEW OF LITERATURE
The Integrated pest management (IPM) is a multidisciplinary ecological approach
to managepest populations by utilizing a variety of control tactics compatibly in a single
coordinated pest management system (Smith, 1978). The philosophy of integrated pest
management was devised simultaneously in many countries after the drawbacks of
unilateral approaches, especially the use of pesticides. Integrated Pest Management (IPM)
does notonly mean the blending of different tactics to achieve an optimum effect but it is
based on ecological principles. The aim is to keep pests at low levels and not to eradicate
them. However, the success of utilization of predators includingspiders as biological
control agent in IPM relies on the sound knowledge of population dynamics, their
biodiversity, effect of different agronomic practices on their spatio-temporal distributional
pattern and their functional role in the suppression of pest in agro ecosystem.
Wheat (Triticum aestivum L.) is one of the most important cereal crops of
Pakistan. It is staple food for the large proportion of our population. It contributes 13.1
percent to the value added in agriculture and 2.8 percent to Gross Domestic Produce
(GDP). Area and production of wheat for the year 2010-11 was 9062 thousand hectares
and 23421 thousand tons respectively (Govt., of Pakistan, 2011). The yield of wheat in
our country is low as compared to our neighboring wheat growing countries like India
and China. Several factors are responsible for low yield including higher incidence of
insect pests (Abbas et al., 2005).In Pakistan, 12 types of minor insect pests have been
reported to infest wheat crop. The important pests are aphids, termites, armyworm and
pink graminous stem borers. Among them, aphids are more damaging one and cause 7.9
to 34.2% yield losses but normally do not cross the economic threshold level (Aheer, et
al., 2006; Akhtar et al., 2010). Up to nineties, there was good natural equilibrium between
aphid population and its natural enemies. Although insecticides are not recommended for
the control of aphids in Pakistan by the Agricultural Department, some wheat growers are
applying insecticides to control aphids in Pakistan on the advice of private agrochemical
sector. Heavy insecticides are also used in the preceding crop i.e., rice. Pesticides are not
only costly, but also causing environmental problems and health hazards. It is
6
apprehended that the natural balance would be disturbed by extensive and indiscriminate
use of pesticides which not only affects population of natural enemies but also disturb
prey- predator relationship. The sole dependence on chemical insecticides fails to provide
adequate protection of crop and results in the outbreak of secondary pests.
Traditionally, biological control was focused on specialist predators but now the
generalist predators such as spiders and coccinellids are gaining importance amongst the
researchers (Symondson, 2002). Spiders are the generalist predators (Dauber et al., 2003;
Holland et al., 2004) which feed almost exclusively on insects and form one of the most
ubiquitous groups of predacious organisms in animal kingdom. Spiders show both
functional and numerical responses to prey densities, although they may not be able to
display long-term tracking of any one particular prey species. By virtue of these density
independent responses, as well as polyphagy in times of low pest levels, theirpopulations
in agro ecosystems are stable and maintained even when pests are absent (Greenstone,
1999; Sunderland, 1999; Hole et al., 2005).
Spiders are known for their ability of killing more prey than the actual
consumption (Nyffeler et al., 1994). This ability qualifies them as successful bio-control
agent. Moreover, spiders can survive even when food is scarce in the fields.As generalist
predators spiders consume a wide variety of prey but concentrate on insect pests. The
population of spiders in the fields depends on the availability of suitable prey. Field and
laboratory data indicate that ground spiders like Pardosaspp. survive and build up their
populations on alternative prey, such as collembolans and dipterans, before the crop is
established and in the first week after crop establishment (Guo et al., 1995; Settle et al.,
1996). Collembolans are the main source of alternative prey to linyphiid spiders in agro
ecosystems and help to sustain and retain spiders as aphid control agent within the crop
area (Agusti et al., 2003), butaphid predation was muchhigher than theconsumption of
collembolans (Kuusk and Ekbom,2012).
A diverse group of spiders may be effective as biological control agent because
they differ in hunting tactics, habitat preferences, and different active periods. Because of
the typical diversity of spiders in an agricultural ecosystem, there will probably be one or
more species that will attack a given pest (Marc et al., 1999). Different spiders feed on
different insects at different times of the day, so a loss in community diversity of spiders
can result in some prey species being released from predation pressure (Riechert and
7
Lawrence, 1997). Variation in body size of both predator and prey species also
contributes to prey reduction, with larger spiders taking larger prey and smaller spiders
taking smaller prey (Nentwig and Wissel, 1986; Nyffeler et al., 1994). In addition, larger
spiders consume disproportionately more prey than smaller spiders (Provencher and
Riechert, 1994).
Density and diversity of spiders is also related to habitat structure (Uetz, 1991;
Balfour and Rypstra, 1998; Marshall and Rypstra, 1999; Wagner et al., 2003). The
biodiversity of spider communities in crop land is important both in terms of enhancing
pest control and understanding the driving forces influencing conservation of nature
(Downie, 2004). But there is a consensus amongst the ecologists that agricultural
intensification affects the biodiversity of agro ecosystems (Swift et al., 1996; Krebs et al.,
1999). Crop management activities like ploughing, hoeing, harvesting etc. cause high
mortality in spiders and perhaps even local extinctions, because spiders density decreases
dramatically after these management practices (Dinter, 1996; Motobayashi et al., 2006).
Studies showed that ploughing, harrowing and sowing reduced 60% spiders density as
compared to unmanaged fields (Duffey, 1978; Dinter, 1996; Thoms and Jepson, 1999).
The ploughed or cultivated fields are generally regarded to have reduced
population of predatory arthropods compared to uncultivated soils (Benckiser, 1997). The
timing and number of cultivations and subsequent seedbed preparations may also affect
arthropod survival and in addition to many others factors such as crop type, the type and
quantity of organic manures, the disposal of crop residues and pesticide use dictate the
ultimate spiders population (Holland and Luff, 2000). Kladivko (2001) summarised the
effects of no-tillage compared to conventional tillage on the spiders and concluded that
larger species were more vulnerable to soil cultivations than the smaller ones because of
the physical disruption and the burial of crop residues that consequently change food
supplies and the soil environmental conditions. The varying degree of tillage effects on
arthropods predators is due to different level of disturbances exercised in different studies
and the time of cultivation (Wardle, 1995).
The zero tillage is characterized by the retention of residues of previous crop,
which ultimately enhances the population of arthropods and collembolans. Reduce or zero
tillage (conservation technology) results in more weeds; more plants residues, less
disturbance, higher soil surface moisture (Wardle, 1995) and proliferation of detritivores
8
(Robertson et al., 1994). Conventional tillage practices have other disadvantages, such as
adversely affecting soil structure, accelerating carbon loss, enhancing evapo-transpiration,
enhancing weed growth, and requiring high nonrenewable energy inputs (Fox et al.,
1991; Shresthaet al.,2006) and reduction of arthropods including
spidersabundance(Motobayashi et al., 2006).
Adjacent and neighboring habitats serve as over-wintering sites and may function
as living refuges for spiders and can therefore act as a source for dispersal into arable
fields, which are frequently disturbed with different management practices (Lemke and
Pöehling, 2002; Schmidt and Tscharntke, 2005; Öberg and Ekbom, 2006). Refuge
habitats may include bush land patches, field edges, roadside verges, domestic parks or
gardens, and planted crops.These living refuge habitats are attractive to beneficial
arthropods because they provide appropriate physical or biological resources in areas
where they have been depleted (Wratten and Van Embden, 1995) and play a key role in
maintaining biological diversity on farmland (Fry, 1994). In some broad acre cropping
systems, refuge habitats are now being used as part of integrated pest management
programmes (Walker et al., 1996; Mensah and Khan, 1997; Tuart, 1999).
The different manners in which spiders forage for a common resource or prey is
called spider guild. There are different guilds of spiders like web-building vs. hunting
species or nocturnal vs. diurnal surely exploit different prey resources, degrees of prey
specialization appear to vary widely at the species level. The structure of spider guild
varied in different crops (Uetz, et al., 1999). Based on structural similarity of spider
guilds, two distinct groups of crops were separated i.e., crops with spider fauna
dominated by ground runners and web wanders (wheat, soybean, alfalfa) and crops with
greater representation of orb weavers and stalkers (cotton, sugarcane and sorghum). The
guilds of spiders found in wheat are orb-web spiders, hunting spiders, ground runners,
ambushers, stalkers, space web spider' sheet web builders.
Habitat manipulation of wheat ecosystem through strip cropping or intercropping
is important in terms of pest suppression (Landis et al., 2000). Plant diversity tends to
intensify the impact of natural enemies thus contributing to the relative infrequent pest
outbreaks often associated with natural communities and mixed crop ecosystems (Pfiffner
and Luka, 2000). Iqbal and Ashfaq (2006) reported that intercropping of brassica in wheat
reduced the aphid population and increased the yield. Potential mechanisms of enhanced
9
predator population in intercropped wheat fields is attributed to the improvement of
availability of alternative foods such as nectar, pollen and honeydew for the natural
enemies such as orb-web spiders and ladybugs of pests (Smith and Mommsen,
1984;Taylor and Foster, 1996; Landis et al., 2000; Tylianakis et al., 2004). Non-prey
feeding or plant derived foods may affect the activity, fecundity and longevity of
predators and these foods can increase their efficacy in biological pest control (van Rijn
and Tanigoshi, 1999; Winkler et al., 2006).
In wheat- rice cropping rotation of central Punjab, Pakistan, the highest abundance
of spiders was recorded in mulched fields of wheat (Schmidtet al., 2004).Crop residues or
mulches reduced evapo-transpiration and increased soil moisture holding capacity
(Teasdale and Mohler, 1993;Jett, 1999), prevented soil erosion (Seta et al., 1993) helped
to promote year-long natural enemy and pest species interactions by providing alternate
food sources and protection from adverse conditions (Tillman et al., 2004). Higher
numbers of arthropod predators, including carabid beetles and spiders were reported in a
crop residue cover (Pullaro et al., 2006; Jackson and Harrison, 2008).
Predator should show some degree of monophagy to suppress populations of a
particular prey. Spiders become more selective, when they have excess of prey (Riechert
and Harp, 1987). It might be counter productive for a spider to feed on any prey since
some might be toxic or deficient in nutrients (Toft, 1999). Some spiders show remarkable
prey preference, despite a wide availability of prey and show the highest growth
efficiency when fed on their preferred prey, indicating adaptation to certain prey type
(Jackson and Li, 2004; Mayntz et al., 2005). In addition, each species of spider occupies a
specific region in the agricultural habitat, from the ground to the top of the canopy.
Different prey species are found in different microhabitats as well. Some web-weaving
spiders also preferentially reject their prey such as Coleoptera, either ignoring them or
cutting them out of the web (Pedigo, 2001). Indeed, many spiders show behavioural
specializations and prey preferences that make them able to effectively limit certain prey
populations. Temporal differences in prey capture activities are found among spiders and
may lead to specialization of diet. Some web-weavers are diurnal, spinning their webs
during day, others are nocturnal. Most hunting spiders that rely on the visual and
vibratory cues are diurnal, but there are exceptions with some hunters active chiefly at
night. Spiders therefore, will only catch prey they encounter during their active period
(Marc et al., 1999).
10
In order to utilize the spiders and other arthropods in wheat integrated pest
management, deep knowledge of their population dynamics, diversity, effect of existing
agricultural practices, surrounding crops, refugia and pesticides on their functional role
and distributional pattern in the suppression of insect pests is imperative. Information
about the diversity, biology and ecology of spiders residing in wheat ecosystems of
Pakistan are scarce. To get the answers of above questions and use spiders as biological
control agents in wheat ecosystems of central Punjab, Pakistan, a detail knowedge of
spiders is required. These informations may also be helpful to establish and evaluate
future management practices for wheat cropin this area.
11
Chapter 3
3. EFFECT OF DIFFERENT AGRICULTURAL
PRACTICES ON SPIDERS AND THEIR PREY
POPULATIONS IN SMALL WHEAT FIELDS
3.1 INTRODUCTION
Spiders are widely acknowledged for their valuablecontributionin the pest
management of agricultural crops.Many studies have reported that they can reduce pest
number and can control pest outbreaks in many agricultural crops(Symondson et al.,
2002).The density of spiders and other predators can be enhanced by changing habitat
management techniques (Landis et al., 2000).If this is achieved early in the cropping
period, before the arrival of the pest population, even a moderate spider density can
suppress the pest ratio in the field (Sunderland and Samu, 2000).
Studies have shown that crop management practices such as irrigation, soil tillage
and fertilization affect the distribution pattern and abundance of the spiders in the
agricultural fields (Frank and Nentwig, 1995;Tuart, 1999; Cloughet al., 2005;Öberg,
2007). Different studies have reported that densities of spider were higher in untilled or
reduced tillage system than in conventionally tilled land cropping system(Robertson et
al., 1994; Motobayashi et al., 2006). Untilled fields have residues of previous cropwhich
enhance predator population including spiders by giving shelter (Rypstraet al., 1999)by
providing alternative prey from the detritivore food chain (Scheu, 2001)andby reducing
intra-guild predation (Finke and Denno, 2002 ; Ramzan et al., 2002, 2005).Herbicides
may reduce population ofphytophagous insects,whichresultinless available prey
forspiders(Amalin et al., 2001).Disturbance created by herbicide can decrease the
population size for more than a month after application(Clausen, 1990).Low- input
farming systems sustain more diverse spiders communities than the intensive farming
systems because of the absence of agrochemicals use (Gluck and Ingrish, 1990).On the
other hand, it is reported that highly fertilized fields support more herbivore and
detritivores and predators as well (Siemann, 1998).
12
Spiders normally take refuge insurrounding natural habitats during the period of
cultivation and disturbance(Halley et al., 1996; Wissinger,1997).Spiders common to agro
ecosystems have been found to move from weeds strips to cereal fields in the
spring(Lemke and Pöehling, 2002)and the proportion of spiders’ webs in the field
correlates with the proportion of foliage in the surrounding habitats (Schmidt and
Tscharntke,2005).Their ability to locate areas of high prey density maximizes their
population growth and enhances long-term pest regulation(Sunderland et al., 1997;
Symondson et al., 2002).Reviews have shown that diversified field boundaries have little
impact on the spider populations as compared with under sowing, mulching and reduced
tillage,which increase pest populations many-fold in the fields (Samu et al., 1996;
Sunderland and Samu, 2000).Polyculture also causes a decrease in the herbivore insect
densities in the fields. The mechanism may reduce colonization rate, oviposition
interference or increased mortality due to predators(Risch,1981; Hooks and Johnson,
2003).
In Pakistan, many farmers have small pieces of land for cultivation. Due to their
social, economic, educational and environmental constraints, different types of
agricultural practices are performed in small areas.So according to the need of the farmer,
there may be a single crop in the field or multiple crops. Crops sometimes may be sown
in well- prepared fields and sometimes in untilled fields due to lack of resources or due to
short sowing time.The present study was designed to check the effect of different field
activities on the same population of spiders and to find outcorrelations between these
practices and agrobiont spider species of the wheat fields. The density of probable food of
spider populations i.e.,collembolans and aphids was also recorded to estimate the effect of
these activities on their population densities.
3.2 MATERIALS AND METHODS
3.2.1 Study Area
This study was carried out at district Sheikhupura (31°43’N, 73°59’E, 209 m
elevation from sea) of Punjab, Pakistan during 2007-08 and 2008-09. For this purpose
two study areas were selected i.e., Adaptive Research Farm Sheikhupura and Adaptive
Research Farm, Farooqabad.The distance between these two study areas was
approximately 25 kilometer. At each area, fivefields were selected randomly and
13
subjected to different crop management activities. In fields 1, 2 and 3, wheat was sown in
conventional way but they differ in surrounding crop. Field I was surrounded byBrassica
napus (BW),field 2 byTrifolium alexandrinum(TW), and field 3 by other wheat fields
(WW). B. napus and T. alexandrinum fields were present only at two opposite sides of the
studied wheat plot. Field 4 was wheat field sown in harvested rice field without tillage
(ZW) and surrounded by conventional wheat.Field 5 was wheat plot without input of
chemical fertilizers (LW) and surrounded by conventional wheat plots. The size of each
studiedfield was approximately one acre. The wheat crop was sown at both sampling sites
in the last week of November and harvested at the end of April. The soil type in all fields
was loamy and alkaline in nature. Irrigation was done by flooding of the fields.
Recommended doses of fertilizers (NPK at the rate of 128, 114 and 62 kg/ hectare) as
approved by the Agriculture Department, was used in all sampling plots except field 5.
Half quantity of nitrogen and full quantity of potash and phosphorous were applied at the
time of seedbed preparation. However, remaining nitrogen was applied with first
irrigation approximately 40 days after sowing. Mixture of herbicides Bromoxynil and
Chlodinafop (at the rate of 1250 ml and 300 g per hectare) was applied 15 days after first
irrigation by using Knapsack hand sprayer (THS-119428) with 3 bar pressure). No
insecticide or fungicide was applied to any plot throughout the experimental period. T.
alexandrinumwas sown in the first week of Octoberand B. napusin the second week of
October. B. napuswas harvested in both years at third week of March. The upper canopy
of T. alexandrinumwas harvested once a month from January to onward. Therefore,T.
alexandrinumwas present even after the harvesting of wheat and finally harvested in the
month of May.
3.2.2 Sampling
Sampling was conducted from December to Aprilafter every ten days. Two
sampling techniques, pitfall traps and visual searching were used at all sites. Epigeic
spiders and collembolans were collected by pitfall traps consisted of cylindrical glass
bottles (6cm diameter x 13cm deep). These were inserted into the ground so that lip was
flushed with the soil surface. Each trap was filled with 250 ml of 70 % alcohol and two
drops of 2% liquid detergent were added to each trap to break surface tension.In each
field, 25 pitfall traps were arranged in 5 x5 grid pattern. Each trap was placed10 m apart
from the other. Traps were operated for 96 hours in the fields and this period constitutes a
14
trapping session in the study. After operation, traps were emptied in the sample bottles
and later spiders were separated from the other invertebrates.
For collection of foliar spiders and aphids, 10 quadrats of 1 x1 m were selected
randomly in each field. Each selected quadrat was approximately 10 m from any other
quadrat. From each quadrat 10 tillers were thoroughly examined from bottom to top of
the plant.The foliage sampling was started in the mid of January and continue till the
harvesting of the crop. To minimize variations, visual sampling was completed in the
pitfall sampling period (= trapping session).Specimens from a single field were pooled for
analysis.
The collected spiders were identified to the lowest possible rank. The immature
spiders, aphids and collembolans were identified only to the generic level.
3.2.3 Data Analyses
The normality of the data was checked using Kolmogorov-Smirnov test (P>0.05).
For calculation, foliage and pitfall data of a trapping session were pooled together. The
richness of the spiders foreach habitat type was calculated using the non parameteric
estimators Chao1 and Jacknife2. To estimate overall species richness in the study Chao2
and Jacknife2 estimates were used. To check thecompleteness of inventories, ratio
between Chao1 and observed richness, andJacknife2 and observed richnesswas
calculated. For comparison of diversity Shanon-wiener index and for evenness Hill’s ratio
(E5)were calculated using the SPDIVERS.BAS program of Ludwig and Reynolds
(1988).The effect of habitat variations on abundance, richness, diversity and evenness
was assessedby nested ANOVA. For this purpose, sampling years were nested within
study sites andstudy sites nested within the habitat types. As in all analysis, sampling sites
and sampling years did not show significant variations, the data of the both years and both
sites were pooled together for further analysis.
To investigate the similarities of habitat types ordination and classification
techniques were used. Cluster analysis was performed using Eucilidean distance and
unweighted pair groupaveraging linkage (UPGMA). For cluster analysis, active density of
only agrobiont species(that constitute more than 1% of the total data).The effect of
agronomic practice on theactivity density of agrobiont families and species was tested
using ANOVA and post hoc comparison of means was doneusing Tukeys’ test(P=0.05).
15
Pearson correlation was used to investigate the relationship among foliage spiders,
aphids,ground spiders and collembolans population. For the analysis program
STATISTICA(Statsoft, 1999) was used.
3.3 RESULTS
3.3.1 Spider Assemblages
During the study, 23,097 spider specimens representing 47 species, 31 genera and
12 families were sampled from five different types of wheat fields. Of the total sample,
37 % individuals were juvenile, 32 % adults males and 31 % adult females. The three
most abundant families were Lycosidae, Tetragnathidae and Oxyopidae that collectively
contributed 75.93% of the total catch.The most abundant species of overall data were
Lycosa terrestris (34.18%), Pardosa birmanica (16.64%), Tetragnatha javana (10.56%),
Neoscona theisi (6.31%), Oxyopes javanus (7.84%), unidentified species of Erigone
genus (7.0%), Bianor albobimaculatus (1.26%), Hassarius adansoni (1.33%) and
Leucauge decorata(2.07%).The collective contribution of these species was 87.12%.
However, abundance of these species varies in foliage and pitfall samples(Table 3.1).
The pooled species accumulation curves (for five habitats combined) showed
thatinitially number of trappable species increased continuously as the number of
individuals increased but after 3000 individuals increase in the species was low even with
continuous trapping and curve reached asymptote (Figure 3.1). The total species richness
was 47.44 and 48.90 on the bases ofChao 2 andJacknife 2 estimates, respectively. The
ratio of observed to estimated number of species was 96 % whichsuggested that at
leastfour percent more species are present in the area than were actually collected.
Estimated species richness for different agronomic practices showed that TW and WW
fields could not be sampled completely as 16% species were missing from these fields
and 12 to 13% from BW and LW fields (Table3.2).
Results of nested ANOVA showed no difference in the activity / density, richness,
diversity and evennessof both study sites and study years. However,fields of variable
agronomic practices differed in the abundance (F4, 280 =11.22;P=0.01) and richness (F4, 280
=35.89;P=0.001) of spider varied in all plots but not indiversity (F4, 280 =1.36;P=0.23) and
evenness (F4, 280 =1.57;P=0.15). Richness (F 14,135 = 115.16;P=0.01) and abundance (F 14,135
= 388.75;P=0.01) also differed significantly during different trapping sessions.The effect
16
of different agronomic practices on species activity / density is also reflected in the results
of Cluster analysis (Figure3.2).Activity / density does not reflect the actual species
density in an area but shows the density of the active spiders. Highest activity / density
was recorded in ZW followed by WW, TW, BW and LW.
17
Table 3.1: Abundance of spiders collected from wheat fields during study period
Families
Species
BW TW ZW WW LW Foliage Ground Total
Araneidae
1782
Neoscona theisi 324 291 290 255 299 1367 92 1459 Neoscona rumfi 5 6 12 8 4 35 0 35 Neoscona excelus 2 4 12 12 1 31 0 31 Neoscona mukerkergei 1 9 18 12 2 42 0 42 Neoscona I 15 12 15 13 8 48 15 63 Neoscona II 8 12 15 11 4 41 9 50 Argiope pradhani 10 9 17 12 3 51 0 51 Crytophora citricola 10 9 16 10 2 47 0 47 Gea sp. 0 1 1 2 0 4 0 4 Clubionidae
5
Clubiona sp 1 2 2 0 0 5 0 5 Gnaphosidae
264
Gnaphosa I 22 37 32 31 17 81 58 139 Gnaphosa II 17 28 27 29 16 84 33 117 Drassodes sp. 1 1 2 1 0 4 1 5 Zelotes sp. 0 1 2 0 0 2 1 3 Hersiliidae
4
Hersilia savignyi 1 1 1 0 1 0 4 4 Linyphiidae
1622
Erigone I 355 308 338 320 301 1212 410 1622 Lycosidae
12501
Lycosa terrestris 1647 1634 1723 1427 1463 808 7086 7894 Lycosa nigricans 14 20 38 77 17 0 166 166 Lycosa maculate 20 52 26 81 30 0 209 209 Lycosa sp.I 0 0 3 1 1 0 5 5 Lycosa sp.II 2 0 2 1 0 1 4 5 Pardosa birmanica 674 878 961 818 512 460 3383 3843 Pardosa oakleyi 18 35 40 52 42 25 162 187 Evippa sp. 1 1 5 7 0 0 14 14 Hipassa sp. 30 9 59 49 31 1 177 178 Oxyopidae
2009
Oxyopes javanus 299 382 424 383 325 1333 480 1813 Oxyopes sp. 37 52 36 40 31 179 17 196 Salticidae
1383
Plexippus paykuli 43 10 34 52 43 1 181 182 Phidiphus sp. 0 2 2 1 0 0 5 5 B.albobimaculatus 46 49 86 51 60 107 185 292 Hassarius adansoni 65 75 66 73 30 92 217 309 Thyne imperialis 51 55 44 47 21 77 141 218 Salticus azhari 8 11 7 7 2 1 44 45 Marpissa tigrina 20 24 32 26 8 67 43 110 Salticidae 1 20 22 32 22 22 75 43 118 Salticidae II 18 22 26 23 15 72 32 104
18
Selenopidae 5 Selenopidae sp. 0 0 3 2 0 0 5 5 Sytodidae
3
Sytodidae sp. 0 0 3 0 0 2 1 3 Tetragnathidae
3028
Tetragnatha javana 491 518 542 422 467 2142 292 2434 Tetragnatha. virescens 18 39 25 22 11 79 36 115 Leucauge decorata 78 94 137 100 70 479 0 479 Thomisidae
491
Thomisidae I 5 8 20 5 4 10 32 42 Thomisus pugilis 23 24 24 23 13 84 23 107 Thomisus elongatus 20 27 25 26 19 52 65 117 Thomisus cherapunjeus 40 37 52 51 26 134 72 206 Thomisus sp. 2 0 0 0 0 1 1 2 Runcina sp. 2 3 10 1 1 5 12 17 G.Total 4464 4814 5297 4606 3922 9341 13756 23097
Key: BW = brassica wheat with different edge
TW = trifolium wheat with different edge
ZW = zero tilled wheat
WW = conventional high input with similar edge
LW = low input
19
Figure3.1: Species accumulation curves for the five different habitats ofwheat field (BW,mixcroppingofbrassicaandwheat;TW,mixingcropping of trifolium and wheat;ZW, wheat sown withouttillage;WW,monoculturewheat;LW,lowinputwheat.
20
Table3.2: Species richness estimates and inventory completeness for each habitat type.
BW TW ZW WW LW
No. of specimens 4464 4814 5297 4606 3922
Observed richness 41 42 46 42 37
Number of singletons 5 5 2 5 4
Number of doubletons 4 2 5 2 3
Chao 1 43 48 46 48 40
Jacknife 2 47 50 46 50 42
%completeness 91 88 100 88 93
21
Figure3.2: Dendrogram for species shared at different habitats types using the unweighted pair group average(UPGMA) and Euclidean distance.Habitats types are coded by BW, mix cropping of brassica and wheat;TW, mixing cropping of trifolium and wheat;ZW, wheat sown without tillage;WW, monoculture wheat;LW, low input wheat.
400
350
300
250
200
150
100
50
Dis
tan
ce
LW
BW
WW
TW
ZW
22
Analyses represent a significant effect ofagronomic practices on the active density
of family Lycosidae (F 14,135 = 2.65;P=0.034), Araneidae (F 14,135 = 115.16;P=0.01),
Tetragnathidae (F 14,135 115.16;P=0.01) and Oxyopidae (F 14,135 115.16;P=0.01). The
active density of agrobiont species was also different in all studyplots;L. terrestris(F 4,290 =
2.65;P=0.034), P. birmanica (F 4,290=19.31;P=0.00), T. javana( F4,290 = 2.55;P=0.039 ),N.
theisi(F 4,290 = 7.63;P=0.00 ),L. decorate(F 4,290 =11.87;P=0.00 ) and O. javanus (F 4,290 =
7.20;P=0.00 ).Comparison of agrobionts in different plots revealed thatL.
terrestris,P.birmanica,L. decorata and O.javanuswere more abundant in zero tilled
fieldswhileT. javana and N. theisi in wheat fields edged with B. napus. Comparison of
zero tilled fields and conventional wheat sowing system showed that active density of all
agrobiont species was high in zerotilled wheat. Except O. javanus and L. decorata, all the
other species were dominant in low- input wheat plots as comparedto conventional wheat
plots (Table 3.3).
It was observed that aphid (pest) population started to appear in the fields at the
end of January and peaked in mid-March (at milking stage of wheat i.e. when the grain
has milk like substance). At the end of March populations of aphids declined (Figure 3.3).
Spiders (predator) population followed the pattern of aphids. Pearson’s correlation
showed that a positive correlation existed between aphids and spider populations in all
studiedplots(r = 0.915 for BW, 0.895 for TW, 0.931 for ZW, 0.875 for WW and 0.654 for
LW; P < 0.05 for all comparison). Significant positive correlation was also observed
between active density of ground spiders and collembolans populations during different
trapping session of all plots (r = 0.887 for BW, 0.849 for TW, 0.931 for ZW, 0.880for
WW and 0.300 for LW; P < 0.05) for all comparison except LW where P>0.05; Figure 3.
4).
23
Table3.3: Difference among habitat types for active density of agrobiont species.
Agrobiont families
Species
Habitat types
Lycosidae
Lycosa terrestris
Pardosa birmanica
Tetragnathidae
Tetragnatha javana
Leucauge decorata
Araneidae
Neoscona theis
Oxyopidae
Oxyopes javanus
Linyphiidae
Salticidae
Bianor albobimaculatus
Hassarius adansoni
WWa< BWab < TWb = LWb< ZWc
WWa< BWab = LWab< TWb = ZWb
WWa< BWab < TWb = LWb< ZWc
WWa < TWb = ZWb = LWb < BWc
WWa < TWb = ZWb = LWb < BWc
LWa = BWa = TWa < WWb < ZWc
TWa = ZWa = WWa = LWa < BWb
TWa = ZWa = WWa = LWa < BWb
BWa = LWa < TWb = WWb < ZWc
BWa = LWa < TWb = WWb < ZWc
NS1
NS
NS
NS
Habitat types having similar superscript letters do not differ significantly.
Agrobiont families/speciesfor the five different habitats of wheat field (BW, mix cropping of
brassica and wheat;TW, mixing cropping of trifolium and wheat;ZW, wheat sown without
tillage;WW, monoculture wheat;LW, low input wheat.
1NS = non significantly different
24
0
200
400
600
800
1000
1200
1400
1600
No
. of
Ap
hid
s/ti
lle
r
Figure3.3: Temporal change in abundance of aphid population in five different habitats of wheat fields (combined for both sites and years). BW, mix cropping of brassica and wheat;TW, mixing cropping of trifolium and wheat;ZW, wheat sown without tillage;WW, monoculture wheat;LW, low input wheat.
25
Figure3.4: Seasonal dynamics of collembolan’s population (combined for two years) in five different habitats of wheat fields(combined for both sites and years). BW, mix cropping of brassica and wheat;TW, mixing cropping of trifolium and wheat;ZW, wheat sown without tillage;WW, monoculture wheat;LW, low input wheat.
26
3.4 DISCUSSION
In different parts of the world, variable number of spidersspecies was recorded
from wheat. Wu et al. (2009) reported 48 species and Clough et al. (2007) 98 species
from China, Pluess et al. (2008) 94 species from Israel,Toth and Kiss (1999) 149 species
from Hungary and Feber et al.(1998) 56 species from England. Difference in diversity of
spiders was due to presence of study areas in different geographical regions (especially
north-south axis) which ledto variable climatic conditions.The present study stretched
from latitude 31° to 33° N.Local diversity can also be influenced by microclimate, site
fertility,habitat structure, habitat heterogeneity, elevation, precipitation and biotic
interactions (Uetz, 1991; Cornell and Lawton, 1992; Huston, 1994; Lawton, 1999;
Mittelbach et al., 2001 and Whittacker et al., 2001). The abiotic (soil acidity, soil
moisture, organic matter content) and biotic (wheat ear height, weed abundance, plant
biomass) factors hadvariable influences on the distributional pattern of different spider
groups(Seyfulina, 2005). The pooled accumulation curve and the ratio of observed to the
estimated number of species suggested that our inventory was 12 to16% deficient in
different studied plots. However, additional use of other methods would capture more
species.
More than half of spiders captured from the wheat fields were lycosids, which
showed a strong preference for wheat habitat. Lycosids are always abundant in close plant
canopy and in irrigated fields (Agnew and Smith, 1989). Higher abundance of lycosids as
compared to other spiders was also noted by Seyfulina (2005) in the wheat fields.
Another possible reason of higher abundance of lycosids in wheat is that the wheat crop
in study area is cultivated after the harvest of rice crop, which is hydrophytic crop and
soil has plenty of residual moisture that favours the lycosids in wheat fields. It is also
reported that activity density and species richness of lycosid spiders were highly
associated with field margins (Öberg, 2007). Wheat fields were divided into small plots
by the dykes in the study area, which were meant to increases the irrigation efficiency but
they also served as refuge for the spiders. These channels have varied type ofvegetation,
which provides food, shelter and over-wintering sites for spiders.The strong dominance of
Lycosidae on the ground may partly be attributed to the extensive use of pitfalls as a
sampling method. It has been found that this familyis highly susceptible to pitfalls (Lang,
2000).
27
Family and species composition of the present study was different from the
findings ofWu et al. (2009). Despite extensive trapping efforts the families Eresidae,
Filistatidae, Miturgidae, Theridiidae, Uloboridae, Sparassidae, Hahniidae, Nesticidae,
Sicariidae,Uloboridae, Dictynidae and Ctenizidae were not recorded. Lycosid species
Pardosa pseudoannulata,Pardosa sumatrana and Lycosa tista recorded in studies done
on the arable fields of India were absent in our data. Similarly, lycosid species Pardosa
astrigera, Parameioneta bilobata, Pirata subpiraticus and Ummeliata insecticeps
recorded from the wheat fields of China were also absent in the present study. Lycosa
terrestris (Butt et al.,2006) was the most dominant lycosid species in the present study
instead of Pardosa pseudoannulata (India)or Pardosa astrigera (China). Tetragnatha
javana (Tetragnathidae) was the most dominant species recorded in foliage sample. This
species is also reported from arable fields of India(Sebastian et al.,2005) but its
percentage is not as high as recorded in the study. This species was not reported from
wheat fields of China (Wu et al., 2009). Two other species i.e., Oxypopes javanus and
Neoscona theisi dominant in foliage of wheat in the present study were also not reported
from India and China.
Although it is reasonable to expect a significant influence of crop characteristics
on the structureof resident spider community, the importance of adjacent habitats must
also be considered (Webb et al., 1984; Duelli et al., 1990). Selective forces of the crop
environment act only on those species that colonize fields from neighboring habitats.
Spider assemblages of alfalfa fields in Virginia are dominated by orb-weaving (42.7% of
total spiders) and web-wandering guilds (37.6%) (Howell and Pienkowski, 1971), while
the same crop grown in Californiaand sampled with identical techniques (sweeping and
D-vac sampling), is inhabited primarily by ground-running spiders (60%) and web-
wanderers (33.6%), which orb-weavers constituting less than 2.0% of all individuals
(Yeargan and Dondale, 1974). Neighboring habitats may also influence the composition
of crop spider fauna indirectly by modifying the dispersal of potential spider prey and
predators in the patchy agricultural landscape (Alvarez et al., 1997; Polis et al., 1997).
Density and diversity of spiders are closely linked with the structural complexity
of habitat (Rypstraet al., 1999), which is often determined by prey availability (Harwood
et al., 2001) and local agricultural practices (Schmidt et al., 2004). High fertilizer usage
led to high primary production in the high input wheat fields (i.e., BW, TW, ZW and
WW) which attracted more prey population (i.e. aphids and collembolans) as compared to
28
low input fields (LW). Higher spider density in zero tilled fields (ZW) as compared to
tilled field (WW) might be due to least disturbance and non inversion of soil.Reduced
tilled fields (ZW) also had more structural complexity due to the presence of straw and
trashes which might had provided more retreats and hiding places because the
temperature and humidity were moderated (Rypstra et al., 1999) and untilled fields also
support more dipterans in agricultural fields (Wardle, 1995), and more collembolans as
compared to tilled fields (Saroj et al., 2005), which are important prey for spiders (Settle
et al., 1996). Reduced tillage results in more weeds and plants residues, less disturbance,
higher soil surface moisture (Wardle, 1995) and proliferation of detritivores (Robertson et
al., 1994). Zero tilled fields support more diversity ofspiders including pests and natural
enemies (Tonhasca, 1993).
Fields with different edges or living refugia habitat (TW) served as over-
wintering sites for spiders and can act as a source for dispersal into arable fields, which
were frequently disturbed with different management practices (Lemke and Pöehling,
2002; Schmidt and Tscharntke, 2005; Öberg and Ekbom, 2006) and play a key role in
maintaining biological diversity on farmland (Fry, 1994). Fields with different edges
showed high active density as the edge crop served as reservoir for spiders and help in the
colonization of the fields (Thomas and Marshall, 1999; Marshall and Moonen, 2002;
Clough et al., 2005). The density of spiders in TW was higher than WW because the
trifolium crop continues untill the last week of May. Moreover, most spiders immigrated
into wheat fields because ofmultiple cuttings and higher frequency of irrigations. Plant
architecture of trifolium is dense which makes the microclimate favourable to spiders.
There are many other agricultural factors such as spatial heterogeneity, habitat type,
fertilizers, tillage, harvesting, which affected the spider density in the fields(Hole et al.,
2005).Low population of spiders was recorded from BW as compared to the WW, which
was expecteddue to short span of brassica crop (brassica was harvested inthe 2nd week of
March each year).The low population of spiders in brassica field(BW) may be due to the
higher density of aphids infesting brassica crop which serves as food for the spiders and it
restricted the movements of spiders into adjacent wheat fields. Another possible reason of
lower spiders density in BW was higher infestation of weeds in brassica fields, because
no herbicides were used to control the weeds. The brassica crop requires less irrigation as
compared to trifolium crop; as a result brassica fields have less moisture as comparedwith
trifolium. Plant architecture of brassica is open which ultimately affects the microclimate.
29
The low-input field (LW) showed the lowest density of spiders as the density of prey
i.e.,aphids and collembolans was less as compared withother habitats. Although, no
fertilizer and herbicides were used, as a result there were more weedswhich may provide
very complex habitats. But due to no use of fertilizer, primary production was badly
affected.The population of prey i.e.,aphids and collembolans were less as compared with
other habitats.
We observed positive correlation between prey and predator population in all
habitats in the present study. Spiders are a major component of the generalist predator
community within arable crops, where they feed on a wide range of major pests including
aphids (Chiverton, 2009; Sunderland, 1999).Spiders in arable land can attain such high
densities that their webs may cover as much as 50% of the fields they inhabit
(Sunderland, 1999). Within wheat fields, it was shown that more than 90% of species
were either confined to the ground or were found both on plants and the ground. Thus, the
majority of species spend time on the ground where they can potentially exploit not only
prey such as aphids, falling from the crop above, but also epigeal invertebrates, such as
Collembolans, as alternative food resources.
30
Chapter 4
4. EFFECT OF BRASSICA STRIPS ON THE
POPULATION OF APHIDS AND ARTHROPOD
PREDATORS IN WHEAT ECOSYSTEM
4.1 INTRODUCTION
Aphids are the major insect pests of wheat (Triticum aestivum L.) in Pakistan
(Hashmi et al., 1983; Hamid,1983; Amjad and Ali, 1999; Aheer et al., 2006; Khattak et
al., 2007).Different species of wheat aphids such as Metopolophum dirhodum,
Rhopalosiphum rufiabdominalis, Rhopalosiphum madis, Rhopalosiphum padi,Sitobion
avenae, Sitobion miscanthi andSchizapis granariumwere recorded from Punjab, Pakistan
(Hashmi, et al., 1983; Inayatullahet al., 1993).Aphids directly suck the cell sap from the
plant and indirect losses are caused through transmission of diseases from infected plant
to healthy plants, which badly affect the yield (Emden, 1979; Abdulkhairov, 1979;
Mohyuddin, 1981; Grimaet al., 1993; Raboudi et al., 2002). Aheeret al. (1993) reported
that 7.19 aphids per tiller reduced the yield of wheat up to 16.38 percent. However, 15
aphids per tiller caused 30-40 percent losses in yield (Kieckhefer and Gellner,
1992).Greatest loss of wheat yield was recorded by aphid feeding during the seedling
stage. Lower losses were recorded during the booting stage; however no damage was
recorded at maturity at same densities of aphids (Kieckhefer and Kantack, 1988).
Densities, and the pest control potential of generalist arthropods predators, are
affected by the stand structure, prey availability, disturbance (Landiset al., 2000) and
plant diversity (Lavandero et al., 2006) of agricultural fields. Increased habitat diversity
in agrarian landscapes also expands the diversity of natural enemy populations, which in
turn diminish colonization rates of herbivorous pest species (Landis et al., 2000;
Baroneand Frank, 2003; Gurr et al., 2003; Lavandero et al., 2006).The population of
generalist's predators such as chrysopids, spiders and coccinellids which have the capacity
to suppress the population ofaphids (Wratten and Powell, 1991; Schmidtet al., 2004) can
be enhanced through habitat manipulation. The best habitat manipulation is intercropping
31
which is simple and inexpensive (Vandermeer, 1995). Studies have reported that
intercropping of canola (Brassica napus L.,) in the wheat fields enhances the population
of arthropods predators (Tingey and Lamont, 1988; Vandermeer, 1995; Altieri and
Nicholls, 1999; Parajulee and Slosser, 1999;Ponti et al.,2007; Sarker et al., 2007).
Potential mechanisms of enhanced population of chrysopids and coccinelids in
intercropped wheat fields is attributed to the improvement of availability of alternative
foods such as nectar, pollen and honeydew for the natural enemies of pests (Patt et al.,
1997; Landis et al., 2000; Tylianakis et al., 2004; Lundgren,2009 and Seagraves et al.,
2010). Honeydew also functions as contact kairomones for feeding coccinellids, which
promotes area restricted search and oviposition (van den Meiracker et al., 1990).
Khan et al. (2005) found that grain yield of wheat increased to 1721 kg per
hectare with wheat and chickpea intercropping (1:1) as compared to wheat alone (1510 kg
per hectare). Iqbal and Ashfaq (2006) reported that intercropping of Brassicanapus with
wheat increased the yield of wheat and reduced losses caused by aphids. Intercropping of
Brassicanapus in wheat also registered higher return than sole wheat crop (Verma et al.,
1997; Ali et al., 2009; Khanet al., 2009).
Nonetheless no such study has been conducted in Sheikhupura agro ecological
zone under rice wheat cropping systems so far. Therefore, keeping in view the above
discussion and importance of intercropping of Brassica napus in the wheat fields for the
suppression of wheat aphids, the present study was initiated. For this purpose, crop of
Brassica napus was selected as intercrop and wheat as a major crop.
4.2 MATERIALS AND METHODS
Field experiments were conducted at three sites i.e., Adaptive Research Farm
Sheikhupura, Adaptive Research Farm Farooqabad and village Bhikie during 2006-07
and 2007-08 cropping season. The distance among the experimental sites was
approximately 15 km. At all sites wheat fields of one acre (67.0×60.36m) were selected
for the experiments. Each field except control was sown in the middle with a belt of B.
napus whose length was across the edges but width varies. In treatment 1 (T1) width was
0.6m, treatment2 (T2) 1.21m, treatment3 (T3)1.82m and treatment4 (T4) 3.65m. Wheat
and Brassica were sown in these fields in the second week of November each year by drill
methods. The recommended dose of NPK fertilizers (128, 114 and 62 kg/ hectare) in the
form of urea, Di-ammonium Phosphate (DAP) and sulphate of potash was applied to all
32
treatments. The tank mixture of herbicides (Buctril-M +Chlodinafop) at the rate 1250 ml
and 300 g per hectare was applied to all treatments in the last week of December each
year to control weeds. However, herbicidal shield spray was used near the Brassica strips
just to save them from herbicidal drift. Brassica was harvested in 3rd week of March each
year, whereas the wheat was harvested in the 4th week of April each year.
4.2.1 Collection of Specimens
Epigeic spiders were collected by pitfall traps both the years from1st December
through last week of April. Chrysoperla trapping was started from February 10 to last
week of April while lady bird beetles (coccinellids ) trapping was started from December
31 to Last week of April.Pitfall traps were made of cheap and easily available glass
bottles (6cm diameter x 13cm deep). During collection, the pitfall traps were buried in the
soil up to level of the ground. At each treatment, 20 traps were operated in 5x4 grid
pattern. The distance between each trap was 10 m. Pitfall traps were filled with 250 ml of
alcohol (75%) and two drops of 5% liquid detergent were added to reduce surface
tension. After three days(=trapping session) traps were removed, capped and brought to
laboratory. Specimens were washed with alcohol and stored in a mixture of alcohol (70%)
and glycerin (30%) with proper labeling of locality, date of collection and other notes of
importance. Collection of aphids was done from January 10 through last week of April.
For the collection of foliage predators (coccinellids, Chrysoperla carnea and
foliage spiders)and aphids, 45 tillers were selected randomly (15 tillers were sampled at
dawn, 15 at noon and 15 at dusk) from each site and at each trapping session. Each tiller
was searched for three minutes for predators population.In the field, specimens were kept
in plastic bags and brought to the laboratory where stored in a mixture of alcohol and
glycerine.
The spiders, chrysopids and aphids were identified to the species level and
coccinellids to genus level with the help of available literature. The immature specimens
were identified only to the generic level. Voucher specimens were deposited at
theDepartment of Zoology, University of the Punjab, Lahore, Pakistan. Each mature
specimen that could not be identified was included as species but its genus was not added
in total of genera.
33
4.2.2 Yield Assessment
The mean values of yield parameters for two years and three sites were calculated.
The wheat data on different yield parameters i.e., number of spikes per m2, number of
grains per spike and 1000 grain weight were collected for each treatment to know the
effect of strip cropping of B. napus on yield. However, the wheat yield was measured on
plot basis (1 acre).The Brassica strips were also harvested and threshed manually.
Brassica seeds and wheat grains were weighed and calculated their values as per local
market prices to evaluate cost benefit ratio among control (sole wheat) and different
treatments used in the study. The yield was estimated on the hectare basis. The increase
or decrease of yield over control was calculated by using formula i.e. Treatment -
control×100/control (Sherawat et al., 2007). The cost and benefit ratio was calculated by
dividing total income by total expenditure.
4.2.3 Data Analyses
Analysis of variance (ANOVA) was used to compare the density of predators and
prey among sites, years and treatments. Pearson’s correlation was used to find out the
correlation between prey and predators population. Statistical software SPSS 13 version
was used to analyze the data.
4.3 RESULTS
During both of the study years highest number of aphids per tiller was recorded in
control plot as compared to treated plots (Figure4.2). The density of aphids did not differ
among the years and sites (F 1, 300 =3.42; P=0.065 for years and F 2, 300 =2.40; P=0.093 for
sites) but significant difference was recorded among treatments (F 4, 270 = 6.11; P<0.005).
Statistical analysis showed that spider density was not different among treatments, study
years and sites (F 4, 300 =1.43; P = 0.225 for treatments and F 4, 300 = 0.26; P = 0.614 for
years and F 2, 300 = 0.38; P = 0.68, Figure4.4).However, correlation was positive between
spiders and aphids population (Pearson’s correlation = 0.69, n= 30, P=0.04).
A significant difference in number of coccinellids per tiller was recorded among
treatments and study years (F 4, 300 =15.63; P<0.005 for treatments and F 4, 300 = 5.93;
P<0.005 for years(Figure4.1). While no difference was observed in their densities among
sites (F 2, 300 = 1.34; P = 0.262). The highest number of coccinellids was recorded in T4
34
while lowest in the control at all sitesunder study. Correlation was positive between
coccinellids and aphids’s population (Pearson’s correlation = 0.47, n= 26, P=0.29).
The analysis of variance for C. carnea population showed that Treatment (4)
revealed their highest and control plots lowest abundance at all study sites (F 4, 209 =16.36;
P<0.005, Figure4.3). But it did not differ significantly among years and sites (F 1, 209
=3.33 P = 0.069 for years and F 2, 209 =0.41; P=0.666 for sites).The increase in the density
aphids also increasesC.carneaabundance(Pearson’s correlation = 0.75, n= 22, P=0.05).
The data of 1000-grain weight of wheat in various treatments are given in Table
(4.1). The results revealed a significant difference among various treatments (F 4, 10 =31;
P<0.005). The maximum 1000-grain weight was recorded in T4 (42.80g). The minimum
1000-grain weight was observed in control treatment (36.57g). The treatment T1 and
control were statistically at par.T3 and T4 were statistically at par followed by T2. There
was negative correlation between population of aphids and 1000-grain weight (Pearson’s
correlation = -0.955, n=20, P=0.001), whereas correlation was positive for Coccinellids
and C. carnea and spiders (Pearson’s correlation = 0.485 n= 22, P=0.27), 0.945 n= 16,
P=0.001) and 0.56, n= 30, P=0.181)respectively). The highest yield was recorded in T3
and lowest in T4. The economic analysis, yield, variable cost and the cost benefit ratios of
aforesaid treatments are given in Table (4.2).The cost benefit ratio of T3 treatment
showed highest value (1:1.95) while lowest cost benefit ratio (1:1.77) was observed in T4.
35
Figure4.1: Population of lady bird beetles among different treatment and sites
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
2006-07 2007-08 2006-07 2007-08 2006-07 2007-08
Sheikhupura BHIKI Farooqabad
La
dy
bir
d b
ee
tle
s /t
ille
r
T1
T2
T3
T4
Control
36
Figure4.2: Population of aphids among different treatment and sites
0
2
4
6
8
10
12
14
16
2006-07 2007-08 2006-07 2007-08 2006-07 2007-08
Sheikhupura BHIKI Farooqabad
Ap
hid
s /t
ille
r T1
T2
T3
T4
Control
37
Figure4.3: Population of Chrysoperla carnea among different treatment and sites
0
0.2
0.4
0.6
0.8
1
1.2
2006-07 2007-08 2006-07 2007-08 2006-07 2007-08
Sheikhupura BHIKI Farooqabad
Ch
rys
op
erl
a c
am
ea
/till
er
T1
T2
T3
T4
Control
38
Figure4.4: Population of spidersamong different treatments and sites
0
20
40
60
80
100
120
140
160
2006-07Sheikhupura
2007-08 2006-07BHIKI
2007-08 2006-07Farooqabad
2007-08
Sp
ide
rs /t
rap
pin
g s
es
sio
n
T1
T2
T3
T4
Control
39
Table4.1: Weight of 1000 grains and yield in various treatments of Brassica napus in wheat field
Treatments No. of spike bearing
tillers m-2
No. of grains
spike-1
1000-grain
weightg
Yield kg
ha-1
% Inc. or
dec. over
control*
T1 380 41 37.77 b 5048 -1.41
T2 375 40 39.77 ab 5338 4.26
T3 374 39 41.75 a 5468 6.80
T4 373 36 42.80 a 4910 -4.10
Control 384 40 36.57 b 5120 -
40
Table4.2: Economic analysis of different treatment of Brassica napuson yield of wheat crop.
Treatme
nts Yield kg ha-
1
Additional
yield over
control
(kg ha-1)
Income of
Wheat
grain
(Rs. ha-1)
Income of
Wheat
straw
(Rs. ha-1)
Income of
B.napus
(Rs. ha-1)
Total
income
(Rs. ha-1)
Total
Expenditur
e
(Rs. ha-1)
Cost Benefit
Ratio
(CBR)
T1 5048 -72 119890 18930 480 139300 77818 1:1.79
T2 5338 218 126778 20018 960 147756 77842 1:1.90
T3 5468 348 129865 20505 1440 151810 77878 1:1.95
T4 4910 -210 116613 18413 2880 137906 77917 1:1.77
Control 5120 - 121600 19200 - 140800 77806 1:1.81
41
4.4 DISCUSSION
In the present study we investigated the effect of Brassica strip cropping in wheat
fields on the population density of pest (aphid) and predators. Our study provided the
evidence that strip cropping (intercropping) enhances the population of the natural
enemies and resultantly suppresses the aphid population.Strip cropping reduces pest
pressure and increases yield of the main crop (Vandermeer, 1995; Altieri and Nicholls,
1999; Tingey and Lamont, 1988; Sarker et al., 2007). This finding is in conformity with
the results of Ponti et al. (2007) and Parajulee and Slosser (1999) who reported canola a
better trap crop for enhancing the population of predators. Potential mechanisms of
enhanced predator population in intercropped wheat fields is attributed to the
improvement of availability of alternative foods such as nectar, pollen and honeydew for
the natural enemies(Patt et al., 1997; Landis et al., 2000; Tylianakis et al., 2004).The
moist and shadier soil surface microclimate also helps to enhance predators population in
the agricultural fields (Zhang and Li, 2003). In general, vegetation diversity has been
proposed to disrupt the pest’s ability to locate the host plant, to increase mortality of the
pest or to repel the pest(Poveda et al., 2008).The Brassica crop is taller than the wheat
crop and also has different colour than wheat crop which may disrupt the movements of
alate aphids. The Brassica crop also has different odour and smell than the wheat crop
which may affects the herbivores. The disruptive crop hypothesisis equivalent to Root’s
(1973) resource concentration hypothesis and stipulates that herbivores in polycultures
will have more difficulties finding crop plants associated with one or more taxonomically
or genetically different plants than finding crop plants in monoculture (Vandermeer,
1989). Finch and Collier (2000) proposed that herbivores tend to land on tall green plants,
so that using non crop plants to make the crop “less apparent” by adding more green or
taller plants is a useful mechanism to camouflage the crop proposed visual camouflage
hypothesisalso known as the “apparency hypothesis” incorporates the visual stimuli(color
and plant height) that induce herbivores to land on plants. Tahvanainen and Root
(1972)suggested that non host plants confer protection to the crop by releasing “odor
masking” substances into the air making the crop “invisible” to the herbivores.Uvah and
Coaker, (1984)reported thatnon host plants emit odors that repel the herbivore. Plant
diversity tends to intensify the impact of natural enemies, thus contributing to the relative
infrequent pest-outbreaks often associated with, natural communities and mixed crop
ecosystems (Huffaker, 1962).Parajulee et al. (1997) reported that the canola crop had
42
higher predator numbers than wheat, suggesting that it would be a better winter inter-crop
in wheat, for enhancing predator numbers.
Negative correlation between seed yield and aphid infestation in the present study
is in accordance with the findings of Tingey and Lamont (1988)whoobserved significant
decrease in yield with the increase ofaphids infestation in the field. Host plants have
direct effect on the herbivores through their physical and chemical properties (Gurr and
Wratten, 1999). The intercropping creates barrier and causes disruption of host findings
for herbivores and could be a feasible explanation for the low density of aphids in the
wheat field (Chabi-Olaye et al., 2005; Bjorkman et al., 2007). Vandermeer,
1989speculatedthat thepurpose of intercropping is to generate beneficial biological
interactions between the crops and it can increase yields, more efficiently use available
resources, reduce weed infestation, insect and disease pressures and provide greater
biological and economic stability.
The economic aspect of this study (Table 4.2) revealed that all intercropping
combinations substantially improved the crop income over sole crops but highest return
of Rs.151810 was obtained from treatment (T3) followed by (T2) Rs.147756 and lowest
return was obtained from T4 treatment Rs.137906. For cost benefit ratio (CBR)
intercropping treatment T3 produced higher CBR (1:1.95) than all other treatments
whereas, T4 produced the lowest CBR (1:1.77). Our results are in conformity with Khan
et al. (2009) who reported that wheat intercropped with rapeseed produced more returns
than sole wheat. However, reduction in returns of treatment (T4) was due to lower yieldof
wheat crop as compared to other treatments.Ali et al. (2009) also reported maximum
benefit cost ratio (1.67) and net profit (Rs.48628/ha) was recorded in wheat Brassica
intercropping systems. Verma et al. (1997) reported that intercropping of wheat and
Indian mustard gave maximum net return, and benefit-cost ratio.
It is concluded from the present study that intercropping of B. napus in wheat
helped to enhance predators’ population in the fields which in turn suppressed aphid
population, thus resulted in natural biological control of aphids. However, low yield of
wheat in T4 as compared to control was due to more reduction in the area of wheat.
Reduction in the yield of wheat crop in (T1) as compared to control may be attributed to
very small area of Brassica which could not attract predators and resulted in inefficient
suppression of the aphid population.
43
Chapter 5
5. EFFECT OF STRAW REFUGIA ON THE
ACTIVITY DENSITY OF ARTHROPODS
PREDATORS AND APHIDS IN THE WHEAT
ECOSYSTEM
5.1 INTRODUCTION
The utilization of natural predators in integrated pest management is an excellent
technique to suppress the population level of the pests in agricultural fields (Delfosse,
2005). Several studies have shown increase in primary production because of insect
pest consumption by generalist predators in winter wheat (Dennis and Wratten, 1991),
rice (Sahu et al.,1996; Mathirajan, 2001), cotton (Ghavami, 2008), corn (Clark et al.,
1994), oats (Helenius, 1990), soybean (Carter and Rypstra, 1995), apple orchard (Marc et
al., 1999) and vegetable (Snyder and Wise, 1999). Some of the most effective arthropod
predators include ladybugs (coccinellidae), rove beetles (staphylinidae) and spiders which
are common in the agricultural fields (Wratten and Powell, 1991; Schmidt et al., 2004;
Ramazan et al., 2005; Sebastian et al., 2005; Motobayashi et al., 2006; Venturino et al.,
2008; Chatterjee et al., 2009).
Agro-ecosystems are generally unfavourable for the generalist predators because
of frequent operations and disturbances. However, modification in agronomic practices
can conserve the abundance of generalist predators in agro ecosystems i.e., preservation
of the overwintering sites in field margins (Pollard, 1968), intercropping (Ferguson et al.,
1984), development of “island" refuge habitats in crop fields (Thomas et al., 1991), cover
cropping, conservation tillage such as zero, or minimum tillage (Smith et al., 1988;
Stinner and House, 1990), and use of physical refugia (Halaj et al., 2000). The main
function of shelter habitats is to provide favourable biotic and abiotic conditions for
growth, reproduction, overwintering and aestivation of predators. Litter such as leaves,
grasses and sticks offer predators a diversity of microhabitats that can ameliorate extreme
physical conditions such as temperature, humidity, light intensity, and wind speed (Wise,
44
1993). Its structure and complexity have strong impact on species assemblages and the
dynamics of guild structure (Riechert and Gillespie, 1986). Spider richness is strongly
correlated with litter depth and its complexity (Uetz, 1979)
Habitat manipulation tactics have number of benefits such as to provide food
resources to predators (Baggen and Gurr, 1998), alternative prey (Stinner and House,
1990; Settle et al., 1996; Abou-Awad, 1998), alternative host (Viggiani, 2003), protection
and shelter from adverse conditions (Landis et al., 2000). The shelter habitat improves
overwintering survival and subsequent fecundity of generalist predators by ensuring pre-
overwintering food for the build up of fat reserves (Sotherton, 1985; Dennis et al., 1994;
Petersen et al., 1996; Petersen, 1999). Prey availability in shelter habitats influence post-
overwintering mortality, fecundity of surviving individuals and phenology of dispersal
into the crop (Thomas et al., 1992; Bommarco, 1998; Petersen, 1999). Shelter habitats
also facilitate reinvasion of areas where reductions of predator population have occurred
due to disturbance of agronomic practices (Lee et al., 2001; Holland et al., 2000).
Nnumerous disadvantages are also associated with habitat manipulation. Cover
crop may lure the pests (Stinner and House, 1990), decrease yield, and increased
weedicides usage as a result of weed problems (Moyer et al., 1994; Buhler, 1995). The
majority of arthropod predators overwinters in the agricultural field margins and disperses
into the crop (Thomas et al., 1992). Overwintering habitat refugia, including hedgerows
and grassy banks, have only meagre spatial influence on crop colonization by predators
(Thomas et al., 1991).
Such a slow colonization of the crop is not sufficient for optimal pest regulation.
Development of permanent overwintering habitats within the crop field results in less
acreage and reduction in crop production. The selection of habitat plays a significant role
in the survival and reproductive success of generalist predators (Riechert and Tracy,
1975; Stearns, 1977).Straw refugia provides a diversity of microhabitats to spiders
including coccinellids and staphylinids that can ameliorate extreme physical conditions
such as temperature, humidity, light intensity, and wind speed (Wise, 1993). The farmers
of China have been using straw bundles to provide temporary refuge for spiders and other
arthropods (NAS, 1977; United States Depatment of Agriculture, 1982). The predators
move into these bundles of straw during the operations like ploughing, sowing, hoeing,
irrigation, insecticide spray and at the time of harvesting of crops. Adoption of this
45
technique amongst the growers in China has resulted in substantial reductions in pesticide
use (50 to 88%), pest control costs (80%), and enhanced crop productivity (NAS, 1977,
United States Depatment of Agriculture, 1982; Wang, 1982). Refugia sustained 5 to 36
times more spider abundance and 18 to 87 times spider egg sacs production as compared
with control. Lycosidae and Linyphiidae families were more abundant in refugia fields as
compared to control fields. About 60% more spider species were recorded in refugia than
control field. Higher density of harvestmen, carabids and staphylinid beetles also
significantly enhanced in habitat refugia (Halaj et al., 2000). But the effects of refugia on
spiders and their preyinteractions are poorly known in wheat ecosystem. In addition, this
technique has not been tested on large scale as a mean to promote the survival of natural
enemies on large-scale arable farming in our conditions.
Wheat (Triticum aestivum L.) is an important cereal crop of Pakistan. It is infested
by few insect pests but aphid is major pest (Aheer et al., 2006; Khattak et al., 2007).
Spiders are the important predators of aphids and suppress the population of wheat aphids
(Schmidt et al., 2004) and can be successfully used in integrated pest management to
control aphids in wheat crop. It is reported that foliage spiders Xysticus cristatus and
ground spider Pardosa spp consumed a considerable number of wheat aphids (Nyffeler
and Benz, 1988; Nyffeler and Breene, 1990; Schmidt et al., 2004). Ground spiders and
cursorial spiders retarded the growth of aphid populations when aphid densities were low
(Birkhofer et al., 2008). Habitat refugia can be used to conserve these predators in wheat
fields. Present study was designed to evaluate the effects of straw refugia as an alternative
to habitat manipulation techniques to conserve arthropod predators and suppression of
pests in wheat agroecosystems.
5.2 MATERIALS AND METHODS
The study was conducted from December 2007 to April, 2009 at four sites of
Sheikhupura district viz., three villages Ghang, Herdev, Ghazi Minara and Adaptive
Research Farm Sheikhupra during wheat season. Trials were conducted on the
progressive farmers fields. The type of soil in all fields was loamy and alkaline in nature.
Average rainfall received during both the years was 5 to 20 mm. At all sites wheat variety
‘Inqilab 91’ was sown through drill in well prepared soil during the third week of
November each year. Recommended doses of fertilizers (NPK at the rate of 128, 114 and
62 kg per hectare), as approved by the agriculture department, were used in all sampling
46
fields. Half quantity of nitrogen and full quantity of potash and phosphorus were applied
at the time of seedbed preparation (in the last week of November each year). However,
remaining nitrogen was applied with first irrigation approximately 40 days after sowing.
All the fields were irrigated through canal irrigation. The tank mixture of herbicides
Buctril M (Bromoxynil+Methyle chloro phenoxy acetic acid) was applied by using
knapsack hand sprayer to both refugia and control fields in the 2nd week of January during
both the years at the rate of 1.25 litres per hectare to control broad leaved weeds.
Wheat ranks first in cropping pattern in terms of allocation of area of farm in the
study area. At each study site two fields approximately of 1.5 to 2.0 acre were selected
and all fields were surrounded by other wheat fields. One field was (control) and in other
field modular habitat refugia were placed (treated). In the treated fields, nine refugia were
placed, each of which was consisted of baskets made of interwoven mulberry twigs
(diameter = 0.3m). Each basket was filled with chopped paddy straw and dried leaves of
Dalbergia sisso which are easily available in study area. The total weight of each
refugium was 550 g which represents the average dry weight of wheat straw m-2 in this
area. In treated field, refugia were placed in a 3x3 grid pattern. The distance of each
refugium was 15 m from the other. First row of refugium was within 1m distance from
the field boundary. To collect arthropods, 9 pitfall traps were installed within one meter
vicinity of each refugium. Each pitfall trap consisting of cylindrical glass bottles (6 cm
diameter ×13 cm deep) were inserted into the ground so that the lip was flush with the
soil surface. Traps were filled with 250 ml of 70% alcohol. To break surface tension, two
drops of 2% liquid detergent were added to the solution. Traps were operated for 72 hours
in the fields and this period constitutes a trapping session in the study. After operation,
traps were emptied in the sample bottles and later spiders, coccinellids and rove beetles
were separated from the other invertebrates. Each refugium was replaced with fresh straw
at the end of a trapping session. In control fields, 9 pitfall traps were also installed on the
same pattern as in the refugia fields.Trapping session started at 7 December, 2nd at 27
December, 3rd at 16 Jannuary, 4th at 5 February, 5th at 25 February, 6th at 17 March, 7th
at 6 April and 8th at 26 April. After collection specimens were brought to laboratory for
identification.Spiders were identified to the lowest possible rank while coccinellids and
rove beetles only to generic level.
To collect aphids, at each site, 30 tillers were selected randomly near the pitfall
traps of refugia and control fields. Adult and nymphs of aphids present on the tillers from
47
the top to bottom were taken into account. The population of aphids was recorded right
from its appearance till harvesting of wheat crop. Similar method was also adopted for the
counting of aphids in the control fields.
5.2.1 Statistical Analyses
The normality of the data was checked using Kolmogorov-Smirnov test (P- 0.05).
For comparison of diversity of spiders Shannon Wiener index and for evenness Hill’s
ratio (E5) and Margalef index for richness were calculated using the SPDIVERS.BAS
program of Ludwig and Reynolds (1988). As beetles were not identified to species level,
the diversity indices not calculated for them. General Linear Model ANOVA was used to
analyze the difference in density and diversity of both years, all sites, and treated and
control plots. The data of both years were pooled as no significant difference was
recorded for all analysis.
5.3 RESULTS
During both study years, 4224 spider specimens representing 40 species, 29
genera and 11 families were sampled from all fields. Of these, 1438 spider specimens
were recorded from control and 2786 from refugia fields (Table 5.1). Most species caught
belong to family Lycosidae. The sample was largely dominated by Lycosa terrestris.
However, Pardosa birmanica was also well represented in the sample. The species
Bianor albobimaculatus, Hassarius adansoni and Thyne imperialis of Salticidae were
also represented by high density in the sample.
Number of species captured from refugia and control plots were different in
Sheikhupura and Ghazi Minara sites (F 1, 16 =9.96 and8.76, respectively;P<0.05).
However, no difference was revealed in Ghang and Herdev sites (P >0.05). Number of
species captured during trapping sessions of all sites varies significantly (F 7, 16=15.24,
21.25, 14.12and 17.36, P<0.05 for Sheikhupura, Ghang, Herdev, Ghazi Minara sites,
respectively. Data revealed that Lycosa terrestris, Pardosa birmanica, Bianor
albobimaculatus and Hassarius adansoni were more abundant in refugia fields as
compared to control fields (Fig 5.1).The abundance of these species was compared by
using t-test.At three sites difference was present (T-Value = -2.63; P-Value = 0.021 for
Sheikhupura; T-Value = -2.20; P-Value = 0.047 for Herdev; T-Value = -2.17; P-Value =
48
0.049 for Ghazi Minara) but no difference was recorded for Ghang site (T-Value = -1.91
P-Value = 0.078).
Overall diversity of spiders between control and refugia plots did not differ from
each other at all study sites (P >0.05). However, a significant difference for diversity was
recorded among the trapping sessions (F 7, 16 = 3.79 for Sheikhupura; F 7, 16 = 4.71 for
Herdev and F 7, 16 = 4.98 for Ghazi Minara and F 1,116 = 3.72 for Ghang, P<0.05).
More spiders were caught from the refugia fields of all the sites than control fields
(F 1, 16 1005.87;P=.000 for Sheikhupura; F 1, 16 230.33 ;P=0.00 for Herdev ; F 1, 16
380.77;P=0.00 for Ghazi Minara). Abundance also varied significantly among different
trapping sessions of all sites (F 7, 16 553.16; P =.000 for Sheikhupura; F 7, 16 15.93; P
=.000 for Ghang; F 7, 16 182.16; P=.000 for Herdev and F 7, 16 246.60; P =.000 for Ghazi
Minara). The abundance pattern of spiders varied from edge to the centre of the field (F 2,
42 90.84; P= 0.000). Thehighest density was recorded at edgeand lowest at centre of the
wheat fields (Figure 5.5).
The density of coccinellids (Figure 5.2) was similar among all sites (P > 0.05), so
data were pooled for further analysis. The density of Coccinellids was compared between
control and refugia plots and significant difference was recorded (F 1, 42 =7.20; P= 0.01).
Density was also different at edge and centre of the field (F 2, 42, =262.92; P = 0.000).
Again the highest density was recorded at the edge of wheat plot followed by margin and
centre of the field (Figure 5.7).
49
Table5.1: Total abundance of each spider species recorded from different areas
Sheikhupura Ghang Herdev Gazi Minara Family Control Refugia Control Refugia Control Refugia Control Refugia
Araneidae Neoscona theisi 1 4 3 5 9 7 8 4 Neoscona I 0 0 0 0 0 2 0 0 Neoscona II 0 8 0 2 0 2 0 2 Erigonidae
Erigone I 9 7 12 9 11 10 7 6 Gnaphosidae
Gnaphosa I 7 4 0 0 1 2 3 4 Gnaphosa II 0 0 2 2 1 2 0 0 Drassodes sp 1 2 0 0 2 2 1 2 Zelotes sp 1 2 2 2 2 1 2 2 Hersiliidae
Hersilia savignyi 0 0 1 2 3 2 0 0 Lycosidae
Lycosa terrestris 154 269 151 301 138 267 154 286 Lycosa mackenziei 0 0 1 2 0 0 0 0 Lycosa nigricans 5 16 0 5 8 9 8 13 Lycosa maculate 5 13 8 10 5 11 6 10 Lycosa sp 0 0 1 5 1 4 0 0 Lycosa sp2 0 0 1 2 1 5 0 0 Pardosa birmanica 71 143 73 132 75 156 80 160 Pardosa oakleyi 6 24 12 7 9 13 7 16 Pardosa annandaleli 0 0 2 2 0 0 0 0 Evippa sp 0 3 0 2 5 4 0 0 Hipassa sp 9 9 7 5 6 11 6 7 Oxyopidae
Oxyopes javanus 12 15 10 17 8 17 11 12 Oxyopes sp 7 7 0 6 0 6 0 2 Saticidae
Plexippus paykuli 11 8 6 3 11 4 6 7 Phidiphus sp 0 6 3 2 0 2 0 4 Bianoralbobimaculatus 11 52 12 50 12 54 13 39
Hassarius adansoni 8 42 5 33 12 39 6 27
Thyne imperialis 2 28 5 25 8 25 2 23 Salticus azhari 1 10 1 4 8 11 1 7 Marpissa tigrina 2 5 2 2 5 5 1 4 Salticidae 1 3 6 4 4 3 4 2 7 Salticidae II 2 4 2 1 4 4 2 5 Selenopidae
50
Selenopidae sp 0 2 1 2 0 2 1 2 Sytodidae
Sytodidae sp 2 2 0 0 2 2 1 2 Tetragnathidae
Tetragnatha javana 9 8 16 14 11 10 7 9 Tetragnatha virescens 4 5 2 2 2 2 4 5 Thomisidae
Thomisidae I 4 4 2 1 2 2 2 4 Thomisus pugilis 2 2 0 2 4 4 4 2 Thomisus elongatus 2 4 2 2 3 3 4 4 Thomisus cherapunjeus 4 4 4 5 0 4 1 3 Runcina sp 2 2 2 2 2 2 2 2
51
0
20
40
60
80
100
120
1 2 3 4 5 6 7 8
Den
sity
/tra
pp
ing
ses
sio
n
Trapping sessions
Refugia Control
Figure5.1: Variation in the abundance of spiders in refugia and control plots
52
0
2
4
6
8
10
12
14
1 2 3 4 5 6 7 8
Den
sity
/tra
pp
ing
ses
sio
n
Trapping sessions
Refugia
Control
Figure5.2: Variation in the number of coccinellids in refugia and control plots.
53
0
5
10
15
20
25
30
35
40
1 2 3 4 5 6 7 8
Den
sity
/tra
pp
ing
ses
sio
n
Trapping sessions
Refugia
Control
Figure5.3: Variation in the number of rove beetles in refugia and control plots
54
0
5
10
15
20
25
30
35
40
45
50
1 2 3 4 5 6 7 8
Den
sity
/tra
pp
ing
sess
ion
Trapping sessions
Refugia
Control
Figure5.4: Variationinthenumberofaphidsinrefugiaandcontrolplots
55
The catch size of rove beetles was high in refugia fields as compared to control
fields (F 1, 42 173.61; P= 0.00; Figure 5.3). The density of Rove beetles was similar among
all sites (P > 0.05 for all sites). The density was also differed at edge and centre of wheat
field (F 2, 42 =75.0; P= 0.000 (Figure 5.6).
The population of aphids started to appear in the month of January (winged form
only). It began to increase in the month of February and peaked at mid March following
the crop phenology. In April population of aphids declined. Non significant difference
among the sites for the population of aphids (F 3, 40 =0.01; P=0.995) was observed but a
significant difference was recorded between the refugia and control fields (F 1, 40 =4.16;
P=.048; Figure 5.4). The population size of spider and both types of beetles increase with
the increase in the abundance of aphids. In the correlation analysis, it was significant
positive only for the spiders population (Pearson correlation = 0.866, P-Value = 0.005 for
the refugia and Pearson correlation = 0.99, P-Value = 0.002 for control).
56
0
5
10
15
20
25
30
35
40
45
50
Edge Margin Centre
Mea
n d
ensi
ty
Refugia
Control
Figure5.5: Abundance of spiders at different distances from edge to centre of field
57
0
10
20
30
40
50
60
70
80
90
Edge Margin Centre
Mea
n d
ensi
ty
Refugia
Control
Figure5.6: Abundance of rove beetles at different distances from edge to centre of field
58
0
10
20
30
40
50
60
Edge Margin Centre
Mea
n d
ensi
ty
Refugia
Control
Figure5.7: Abundance of coccinellids at different distances from edge to centre of field
59
5.4 DISCUSSION
It is evident from the results of the study that straw refugia within wheat fields
had a pronounced effect on the abundance of predatory fauna of wheat ecosystem.
The increased population of arthropod predators may be due to many factors. In the
experiments, agronomic practices were kept constant at all sites. So it is assumed that
a major increase in the abundance of predator fauna may be due to the addition of the
straw refugia in the field. Average seasonal density of the spiders and studied beetles
increased approximately 1.5 times than control plot. Halaj et al. (2000) reported that
modular habitat refugia increase 5 to 36 times the spider density and increase 60%
spider species as compared to control plots. A significant increase in the abundance
ofother predators like harvestman, carabid and staphylinids beetles was also reported
from refugia plots. In present study, the number of beetles increased in abundance in
refugia plots but that increase was not significantly different from control plots. The
number of spider species also did not vary in the control and refugia plots. The
richness depends on the complexity of the habitat. In the present study, both control
and refugia habitats were similar to each other except the presence of refugia. These
refugia are based on dead material which provide shelter to only ground predator and
prey species. It did not add much new to the habitat complexity. As a result of which
density of ground living predator species increases but richness remains same in
control and refugia plots.
The availability of alternative preys enhances the predator activity density in
agroecosystems (Settle et al., 1996; Wise et al., 1999). Brust (1994) stated
thatdetritivores, get energy from the decaying refugia which ultimately increase the
abundance of arthropods predators. Due to refugia, higher number of spider egg sacs
and egg sac guarding females were recorded from the field. It shows that mulch
provides more favorable conditions for egg development and increased food supply
for their young ones. The main factor may be the availability of the food to the
predator populations.
It was also recorded that that the population of aphids decreased significantly
in the straw refugia treatment as compared to control. These results are totally
different from (Veronica et al., 2010) who reported less number of predators and
higher density of pest Microtheca ochroloma Stal (Coleoptera: Chrysomelidae), the
60
yellow-margined leaf beetle, in turnip crop in refugia plot. It could be that the absence
of mulch facilitated the searching behavior of the predators on both the soil and the
plant. Although M.ochroloma larvae and adults occur more frequently on the foliage,
the larvae do move to the lower parts of the plant and to the leaf litter to pupate and
the adult females move to the leaf litter and soil to deposit eggs. This behavior in plots
without straw mulch may make the prey more susceptible to predation by ground
predators, whereas in plots with the structurally complex straw mulch the larvae and
adults can easily hide and escape predation from the fewer ground predators.
Other factors that may affect pest and predator populations are differences in
plant quality and soil moisture. For example, turnip plants in the plots with straw
mulch were larger (more leaf biomass), thus presenting higher quality host plants to
the pest. It may be due to difference in methodology and nature of crop. Wheat is
dense crop whereas the turnip crop has almost open canopy. Pests and predators are
also different as compared to our study. So the difference in behaviour, physiology
and activity pattern cause variation in the results.
It is considered that mulch (refugia) may be used as integrated pest
management techniques. Prasifka (2006) reported that the mulches can be used in
IPM along with other agronomic practices. However, he himself admitted the flaws in
methodology and techniques used in his experiments. It was reported that the squash
bug, Anasa tristis (DeGeer), and the American palm Myndus crudus Van Duzee, were
favored by the use of organic mulches (Howard and Oropeza, 1998; Cranshaw et al.,
2001). The use of organic mulches in other cropping systems has resulted in a
decrease in pest populations. This has been observed for the onion thrips, Thrips
tabaci Lindeman, in onions (Larentzaki et al., 2008), the silver leaf whitefly, Bemisia
argentifolii Bellows and Perring, in zucchini squash (Summers et al., 2004), and the
Colorado potato beetle, Stilodes decemlineata (Say), in potato crop (Johnson et al.,
2004).
Refugia also increase spatial diversity and could increase spider density from
reduced intraspecific competition in the experimental plots. Increasing spider numbers
with habitat complexity in agricultural systems could allow spiders to reduce specific
pest problems through maintaining the balance of insect species (Manns et al., 2008).
61
Generalist predators are absolutely dependent on the physical structure of their
environment. Many studies have reported (Chiverton and Sotherton, 1991; Uetz,
1991; Ramzan et al., 2002; Salim et al., 2003) higher density of spider as compared to
staphylinids (Rove beetles) and coccinellids in mulched plot as compared to no mulch
plots. Higher abundance of Staphylinids in refugia plots as compared to control plots
was recorded; it may be attributed due to higher moisture level and humid
microclimate in refugia (Basedow, 1994). Rove beetles are reported to be
polyphagous and their food on ground ranges from algae, fungi, collombolans and
decaying organic matter (Good and Giller, 1991).
Difference was observed in the abundance of coccinellids between the
treatments, although non significant statistically. It may be due to reason that these
predators reside mainly on foliage and not on the ground. As we have used only pitfall
traps to capture predators, their number was low in these traps.
Our study shows that the population of aphids decreased significantly in the
straw refugia treatment as compared to control. But it is fact that population of aphid
crosses the ETL in both the treatments in the mid of March each year. Several studies
have shown relation between the use of mulch and a decrease in pest populations
(Wise et al., 1999; Way and Khoo, 1992; Sunderland and Samu, 2000). These studies
assume that beneficial arthropod populations are responsible for the decrease in the
pest population and that mulch improves beneficial arthropod habitat by offering
cover from their own predators, protection from sunlight, moist soil, and increased
nesting sites. There is an evidence for the reduction in the density of aphids and
increase in the population of arthropods predators in mulched plots (Schmidt et al.,
2004) and it can be used successfully in combination of other control tactics.
Abundance of spiders, coccinellids and rove beetlescollected from refugia and
control fields decreased as the distance from the field margins increased. Higher
densities of spiders especiallylycosidswere found at the field margins(Holland et al.,
1999). Higher activity density of spiders,coccinellids and rove beetles at field margins
suggest that field margin is an important habitat for these predators. Permanent grassy
vegetration or weedy borders or non agricultural habitats at field margins provide
shelter, over-wintering sites and alternate food source for predatorsin frequently
62
disturbed habitats such as conventional agricultural fields (Nentwig, 1987; Hausela-
Veistola, 1998; Clough et al., 2005; Öberg, 2007).
63
Chapter 6
6. PREDATION OF SPIDERS ON INSECT PESTS
OF WHEAT CROP
6.1 INTRODUCTION
Spiders are among the most abundant and diverse generalist predator in
agroecosystem. All spiders are predaceous and play a key role in the suppression of
the herbivore insect pests (Marc et al., 1999;Symondson et al., 2002; Nyffeler
andSunderland, 2003).Most of them feed on different insect taxa andshow both
functional and numerical responses to their prey densities. However,they cannot track
one particular prey species for a long time in agroecosystem. Their density
independent responses and polyphagy enable them to persist in agroecosystem during
the period of low prey density and slow down the buildup of insect pest population in
early season (Greenstone, 1999, Marc et al., 1999, Hole et al., 2005).The role of
spiders as biological control agentmay increase with the density (Lang et al., 1999);
high abundance of spider may reduce herbivore population because of increased
predation rate (Carter and Rypstra, 1995). However, high spider densities also cause
intraguild predation and cannibalism that release pest from predation pressure and
increase their abundance in the field (Wagner and Wise,1997; Synder and Ives, 2001).
Spiders usually aggregate in the area where food is abundant (Harwood et al.,
2003). Decisions of foraging patches are directly related with their fitness i.e., growth
and reproduction (Uetz, 1992; Toft and Wise, 1999; Bilde and Toft, 2000). Spiders
maximize their fitness by optimal balancing of nutrients rather than by maximizing of
energy consumption (Toft, 1999). So indiscriminate feeding may be disadvantageous
to the organisms due to variations in the quality of the prey (Uetz, 1992; Toft and
Wise, 1999; Bilde and Toft, 2000). Prey preference usually based on the quantity and
quality of prey available in the feeding patch, age and size of predator, habitat
structure and weather conditions (Riechert and Lockley, 1984; Wise, 1993; Pitt and
Ritchie, 2002; Miller et al., 2006). The compositions of the diet also change with the
internal state and experience of the spider (Toft, 2005). Feeding rate of female is
64
higher than male spiders because females require extra energy for reproduction
(Walker and Rypstra,2001). However, the consumption per unit weight and the
proportion of food assimilated fluctuate little between the instars and within an instar
(Isikber and Copland,2001).
In wheat fields of Punjab, Pakistan, aphids are the most abundant pests
although these rarely cross economic threshold level. Hashmiet al. (1983) reported
attack of four species viz., Sitobion avenae (F.), Schizaphis graminum (Rond.),
Rhopalosiphum rufiabdominalis (Sasaki) Rhopalosiphummaidis (Fitch) on wheat crop
in Pakistan. Other pests such as stem borer, Sesamia inferensWalk., and Oriental army
worm, Mythimna separata Walk cause serious damage occasionally. Yield losses are
influenced by the stages of the crop at which attacks of pest occur and environmental
conditions of the area. Change in the farming system such as introduction of high
yielding varieties, increased use of fertilizers, increase area of irrigated crop,
continuous rotation of rice and wheat has increased the losses due to these pests
(Sharma et al., 2002). These pests decrease productivity of the fields by reducing the
quality and quantity of grain yields (Aheeret al., 2006; Khattak et al.,2007). The
natural enemy complex of wheat in Punjab, Pakistan is dominated by generalist
predators which also include spiders. Three species of hunting spiders,Lycosa
terrestris (Family Lycosidae), Pardosa birmanica (Family Lycosidae)and Oxyopes
javanus(Family Oxyopidae) are most abundant in the wheat fields throughout the
season (Butt and Sherawat, 2011). Many studies have reported impact of spiders on
common agricultural pests, such as aphids (Nyffeler and Benz, 1987; Mansour and
Heimbach, 1993; Lang, 2003). However, their abundance is not sufficient to prove
their effectiveness as biological control agent. The aim of present study was to
investigate the predatory efficacy and prey preferences of the most dominant hunting
spiders of the wheat crop. For this purpose, we assessed the predatory potential of
spider against wheat pest by choice and non- choice feeding experiments in the
laboratory. In addition, information about the predation preferences of these spiders
were also collected from the fields and compared with the lab studies.
65
6.2 MATERIALS AND METHODS
For the experiment, adult spiders of both sexes were collected alive from the
wheat fields during January through April 2010 using sweep net and suction device.
Spiders were stored singly in the 50 ml plastic cups containing sand, crumpled paper
towel andleaves for shelter and moisture. Muslin cloths wrapped around the mouths
of the cup and held tight by rubber bands. Spiders were kept at room temperature (22
to32°C), 55-65% humidity and a light: dark cycle of 14:10 h. No specimen was used
more than once in the experiment.
To determine the killing potential of these spiders, Ist and 2nd instar larvae of
Mythimna separata(armyworm) and Sesamia inferens (pink graminous stem borer),
and 4thnymphal instar and apterous adult of Sitobion avenae (aphid) were used as
prey. These insects are common pests of the wheat fields in the study area. Larvae
ofS. inferensand M. seperatawere obtained from the laboratory of Agriculture
Department, Sheikupura. However, aphids (nymphs and adults) were collected from
the wheat fields and kept alive in the laboratory on the wheat plants.
6.2.1 No-choice Feeding Tests
Feeding experiment with six types of prey (i.e., larvae of first or second instars
of stem borer or armyworm, nymph or adult of aphids) was conducted in the lab to
assess the predatory potential of agrobiont spider species. Before laboratory
experiment, spiders were fed with a mixture of insects collected from the wheat fields
to the satiation level and then starved for four days to standardize the hunger
levels.Single starved spiderwas placed in a container (12.5 cm diameter, 3.25 cm
height) and only one type of food was provided in excess. For this experiment,120
spiders of one species were used and repeated twice at different time. The container
was examined after24 h and numbers of dead prey items were recorded. Control
containers (n = 10) containing ten specimens of each prey type but no spider, was
used to assess the number of larvae or nymphsdied during same time.
6.2.2 Choice Feeding Tests
This test was performed to assess the predatory preference of agrobiont
spiders in the presence of different types of prey. The procedure was similar as
described in non-choice feeding experiment. However, in the test single starved spider
66
was exposed to mixture of all preysmentioned earlier. Ten specimens of each prey
type were placed in the container and dead specimens were recorded after 24 hour.
6.2.3 FieldObservations for the Predators
To record the diet composition of spiders in the field,direct observations
(separately for each species by a single observer) were made from January through
April 2010. For this purpose, two wheat fields approximately 500 meters apart were
selected. These fields were not treated with pesticides and herbicides. All the
predators were diurnal so data were not recorded at night. In the field, observations
were conducted for 1 h at following times:06:00, 09:00, 12:00, 15:00, and 18:00 per
day. We walked in the field randomly and if found a spider with a prey, tried to
identify the prey to the order level. Whenever possible spider was captured and
brought to the laboratory for the identification of the food.To record the seasonal
change in diet composition, insect pests from one-meter square area were collected
each month by vacuum sampler and sweep net before field observation and identified
them to the order level.
6.2.4 Statistical Analyses
Before any statistical analyses, normality of the data was checked using
Kolmogorov–Smirnov test. The differences in the killing rates of spiders in the
experimental vs. control containers and in their diet composition were assessed using
ANOVA. In order to find which of the three hunting spiders was most active in killing
or consumption of pests Tukey’s test was used.Wilcoson signed-rank test was used to
compare the monthly diet of three spider species in the fields. To assess seasonal
variation in the diet of a species Friedman test was applied. The difference in the
feeding preferences of male and female spiders was checked using paired t- test.
6.3 RESULTS
6.3.1 Non- Choice Feeding Test in Laboratory
Results test showed that in the laboratory each of the three hunting spiders
consumedall types of prey offered to them (Table 6.1). Aphid nymph was the most
consumeddiet ofall species (F5, 54 = 18.64 forL. terrestris, 16.35 forP.
birmanicaand21.47 for O. javanus, P< .01). The feeding potential of O. javanus was
67
more than L. terrestris (t = -6.90; P = 0.000) and P. birmanica (t =-4.71; P = 0.00).
However, no difference was observedin the consumption rate of L. terrestris and P.
birmanica (t = 1.80; P = 0.08).Consumption rate of females (all species)was higher
than males in the studied spider species (t =-4.32; P =0.002 for L. terrestris; t =-3.80;
P = 0.004 for P. birmanica and t = 4.54; P = 0.001 for O. javanus).
6.3.2 Choice Feeding Test in Laboratory
Prey preferences of three hunting spiders are similar as based on the choice
feeding experiments. All the spiders prefer to feed on aphid nymph as compared to
other available prey(Table 6.2). A significant low consumption of all food items was
recorded in this experiment as compared to non-choice feeding experiments
(Figure6.1). The comparison of thepest-killing rate of three species showed O.
javanus to be the most active hunters than other species (F2, 87 =122.85; P < 0.001 for
males and F2, 87 =158.65; P < 0.001 for female). Killing rate of females was higher
than males spiders in all species (t = -3.32; P = 0.009 for L. terrestris; t = -2.98; P =
0.015 for P. birmanica and t = -3.62; P = 0.006 for O. javanus).
6.3.3 Field Observations
During the study,297 specimens ofL. terrestris, 254 of P. birmanicaand 240 of
O. javanus were observed in the field. Data showed seasonal change in the food
pattern of all the studies species (S=21.17, P= 0.007 for L. terrestris, S=17.53, P=
0.025 for P. birmanicaand S=21.69, P= 0.003 for O. javanus). In January,
collembolan was major food of lycosid spiders. With the change in the season,
homoptera and diptera become abundant in the diet. However, O. javanusmainly
consume homoptera and diptera specimens (Figure6.2). Results of our field
observation indicated thatHomoptera, Diptera, and collembolan constitute main prey
of three hunting spiders during study period (Table 6.3). Other prey orders consumed
by hunting spiders include, Coleoptera, collombolan, Dermoptera, Hymenoptera,
Lepidoptera, Orthoptera and others (unidentifiable prey).Monthly diet composition of
the three hunting spiders did not differ statistically (Wilcoson signed-rank test, P >
0.05; Figure 6.2). Body measurement of wheat insect pest and three hunter spiders
have been shown in Table (6.4).
68
Table6.1: Mean number of prey killed by different sexes of huntingspidersafter24hofexposureinnochoicefeedingexperiment
Predator Sex S.B.
1st ins.
S. B.
2nd ins.
Army-
wormIst
instar
Army-
worm2nd
instar
Aphid-
nymph
Aphid-
adults
Lycosa
terretris
Female 6.30 0.38 4.20 0.40 5.2 0.33 4.80 0.51 7.50 0.57 5.43 0.58
Male 5.06 0.45 4.23 0.41 4.1 0.58 3.93 0.45 6.26 0.51 4.82 0.61
Pardosa
birmanica
Female 6.75 0.36 5.25 0.33 6.7 0.33 5.65 0.31 8.25 0.26 6.21 0.55
Male 5.15 0.55 4.65 0.34 6.0 0.29 4.35 0.33 7.51 0.36 5.42 0.56
Oxyopes
javanus
Female 8.25 0.57 7.70 0.50 7.5 0.45 6.2 0.64 9.51 0.15 7.12 0.61
Male 6.35 0.54 6.50 0.62 6.45 0.65 5.45 0.63 8.22 0.83 5.25 0.62
69
Table6.2: Mean number of prey killed by different sexes of three huntingspiders at 24 h of introduction in choice feeding experiment
Predator Sex Stemborer
Ist instar
Stem borer
2ndinstar
Armywor
m Ist
instar
Armywor
m2nd
instar
Aphid
Nymph
Aphid
Adult
Lycosa
terretris
Female 1.0 0.17 0.550.19 0.1 0.08 0.0 0.00 4.6 0.37 2.7 0.12
Male 0.8 0.11 0.4 0.11 0.1 0 .07 0 .0 0.00 3.2 0.45 2.3 0.19
Pardosa
birmanica
Female 1.5 0.21 1 0.04 1.2 0.11 0.8 0.26 5.5 0.43 3.2 0.21
Male 0.9 0.08 0.3 0.07 0.5 0.09 0.4 0.12 3.9 0.51 1.8 0.13
Oxyopes
javanus
Female 2.9 0.15 0.8 0.19 1 0.12 0.6 0.16 6.8 0.69 4.2 0.61
Male 2.3 0.12 0.6 0.21 0.5 0.08 0.2 .04 4.2 0.61 3.4 0.37
70
Figure6.1: Variation in number of killed prey items during no- choice and choice feeding experiments. A:Lycosa terrestris, B:Pardosa birmanica and C:Oxyopes javanus
I Si: first instar of Sesimia inferens; II Si: second instar of Sesimia inferens; I Ms: first instar of Mythymna separata; N Sa: nymph of Sitobion avenae; A Sa: adult of Sitobion avenae
71
Figure6.2: Seasonal change in the diet composition of hunting spiders. A:Lycosa terrestris, B:Pardosa birmanica and C:Oxyopes javanus
A
B
C
72
Table6.3: Average consumption or killing (%) of various insect orders by three hunting spiders in the wheat fields during a season.
Insect order L. terrestris P. birmanica O. javanus
Homoptera 25.3 21.9 35.1
Diptera 14.5 13.8 20.8
Lepidoptera 3.4 4.7 2.5
Orthoptera 3.4 2.4 3.3
Hymenoptera 5.7 7.5 5.8
Coleoptera 10.5 7.3 10.4
Collembola 21.3 30.1 0
Dermoptera 1.0 1.6 2.1
Unidentified 14.9 12.2 20.0
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Table6.4: Body measurements of wheat insect pests and three huntingspiders used in the experiment.
Spiders/insect pests Size (mm)
Lenght Width
Lycosa terrestris male 5.43 ±0.35 2.88± 0.21
Lycosa terrestris female 6.70±0.44 2.68±0.26
Pardosa birmanica male 5.40±0.78 2.88±0.38
Pardosa birmanica female 5.50 ±1.22 2.30±0.7
Oxyopes javanus male 5.14 ± 0.25 2.37 ±0.20
Oxyopes javanus female 6.2±1.41 2.74±0.2
Stem borer 1stinstars 1.7+0.50 0.38+0.17
Stem borer 2nd instar 2.25+1.18 0.45+0.20
Armyworm 1stinstar 1.8±0.11 0.40±0.09
Armyworm 2nd instar 2.4±0.33 0.5±0.12
Aphid nymph 1.2±0.13 0.5±0.07
Aphid adult(Apterous) 2.1±0.35 0.9±0.12
74
6.4 DISCUSSION
The food spectrum of the ground living spiders, such as wolf spiders (lycosidae),
consists of prey species of different trophic level including herbivore insect pests of crop
like aphids, detrivore, conspecifics and other predators (Wise, 1993; Oelbermann et al.,
2008). Studies have reported spiders as main predators of aphid in wheat crop and other
cereals (Sunderland et al., 1987; Kajak, 1995; Nyffeler and Sunderland, 2003). In the
present study, all the three hunting spiders consumed aphids (both nymphs and adults) in
more number as compared to other food items offered in both choice and no choice
feeding experiments. Nyffeler and Benz (1982) reported that in agroecosystem aphid
constituted 25% of the diet of lycosid spiders.
In the present study, all species are hunting spiders but L. terrestris, and
P.birmanica(Lycosidae) live on ground and make burrows in the soil between the crop
rows while O. javanus(Oxyopidae)live on foliage. The prey used in the experiments was
mainly foliage dwellers and approximately of equal size (Table 6.4). Although, lycosids
predominately hunt on the ground but field observations and gut content analysis proved
that they climb to the foliage and hunt herbivore pest species (Pollet and Desender, 1987;
Sunderland et al., 1987; Nyffeler and Benz, 1988). Winder et al. (1994) reported that a
large number (37-348 m-2 day-1) of aphids (dead and live) falls on the ground and remain
available to the ground spiders. Lycosids are not scavengers so available dead aphid are
useless to them. Live aphids return to the crop canopy in just 6.7 minutes. So their
availability is continuous but low to lycosid spiders on the ground. L. terrestris and
P.birmanicain this study also climbed to wheat plant and capture prey there. However,
the movement of P.birmanicawas restricted to the lower part of the plant (pers. obs.).
Similarly, the specimens of O. javanuswere also captured from the ground surface. So
studied species have similar ability to catch prey in the field.
Toft and Wise (1999) reported that aphids are poor quality prey that allowed
neither growth nor development of the spiders. That is why spiders prefer other food
sources to maintain their population in the field (Bilde and Toft, 1997; Beck and Toft,
2000). In the present study, spiders killed all types of offered prey in both choice and no
choice feeding experiments. In the choice feeding experiment, the number of aphid killed
was low as compared to non-choice feeding experiments. This showed that availability of
high quality prey (larvae of stem borer and armyworm) results in a decrease in the control
75
of aphids. Some previous studies also reported decrease in the predation of spiders on the
aphids in the presence of alternative prey (Bilde and Toft, 1997; Nyffeler and Sunderland,
2003), while some studied denied it (Sunderland, 1985, 1986; Toft, 2005). Lycosid
spiders preferred mix diets even if single prey types were highly available (Wise, 1993).
Consumption of low quality prey depends on the nutritional balance of the spiders. Those
spiders which were nutritionally balanced they consumed three times more aphid than
nutrionally imbalanced spiders (Mayntz and Toft, 2001). Toft (1995) also reported that
hunger level of spider has no effect on the consumption rate of aphid. Although pure
aphid diet has little or no effect on growth and development of spiders but it is not useless
as food. In starved conditions, pure aphid diet increase survivorship in linyphiid and
lycosid spiders. Thus, in a situation of low food availability, aphid consumption helps to
maintain spider population in the agricultural fields.
Field studies showed that Diptera constitute major part of the food after the aphids
in all the three hunting spiders. Some other studies also reported that Diptera is a high
nutritional value food for the spiders and makeup 25-32 % of the food of wolf spiders.
Although, lycosid spiders in the long term may suffer from nutrient deficiency when
feeding exclusively on Drosophila melanogaster (Toft and Wise, 1999; Oelbermann and
Scheu, 2002).Therefore, predator shift to alternate prey such as collembolan when pest
species are of low quality which affect their pest control potential (Bilde et al., 2000).
Tahir and Butt (2009) reported that O. javanus consumed more Lepidoptera in rice fields
as compared toL. terrestris and P. birmanica. But in this study, no significant difference
was recorded in the proportion of Lepidoptera in the diet of three hunting spiders. This
might be due to the difference in abundance and diversity of Lepidoptera in rice and
wheat fields.
Female spiders were voracious predators and consumed more insect pests than the
males under similar conditions. Females usually need more energy for oviposition and
brood care, while males need only the essential energy for survival (Kim, 1992). This
finding supports the hypothesis of males as time minimizers and females as energy
maximizers (Walker and Rypstra, 2001). In present study also female of each spider,
species consumed more prey as compared to male. All these three species of spider will
reproduce in the coming month after hibernation, so for them main goal may be to store
energy for reproduction.
76
The consumption of prey in the field and laboratory could not be correlated with
each other. In the laboratory, consumption of wheat pests was high as compared tofield
data. The use of enclosed arena for the experiments altered the abiotic conditions
experienced by the animal. Such changes included radiation, air and ground temperature,
wind speed and relative humidity. It also increased prey – predator encounter rate and
decreased cover for the prey organisms.
This study has shown that the studied spiders have potential to influence the wheat
pests in the field but still needs to prove that it actually happens in natural unmanipulated
field conditions. However, the consumption rate of pests was low in the field data but the
number of the studied species was very high which increase their interaction with the pest
population. Along with these species, a large assemblage of the spider was recorded in the
wheat field (Butt and Sherawat, 2011) which suggested that they will be helpful in
controlling even those pests which are not beneficial for these predators. During the
period, when preferred prey is scarce, feeding of spider on alternative foods facilitates to
maintain high spider density in the fields. This behavior of spiders is important for the
biological control of insect pests in the fields.
77
Chapter 7
7. EFFECTS OF PESTICIDES ON AGROBIONT
SPIDERS IN LABORATORY AND FIELD
7.1 INTRODUCTION
In the agricultural fields communities of natural enemies are usually affected by
pesticide application, either due to direct contact or drifting of spray. Many studies have
reported the adverse effects of pesticides on non target organisms including natural
predator species that feed on herbivorous insect pests (Paul and Thygarajan, 1992). The
extensive use of pesticides has reduced the efficiency of natural control predators in the
agro-ecosystem. Pesticides may cause death of biological control agents or may change
their longevity, reproduction, development, physiology and mobility (Moura et al., 2006).
Natural enemies are usually more susceptible to the effect of pesticides than their
prey due to their small size, searching habit and less development of detoxifyning
enzymes (Charlet, 1995). Spiders are the important predators and suppress the population
of insect pest of different crops (Holland et al., 2004; Schmidtet al., 2004;Pearce and
Zalucki, 2006; Chauhan et al., 2009).They consume variety of small sized and soft bodied
preys without inflicting damage to field crops (Holland et al., 2004) and are important
due to their abundance and high predatory potential (Nyffeler and Benz, 1987; Wise,
1993). Many pesticides have long residual activity. Residual activity of pesticides is
generally correlated with temperature. Generally, a pesticide remains active for longer
time when temperature is lower due to reduced vaporization. Microbial degradation of
pesticide is inhibited by low temperature, resulting in longer residual efficacy (Felsot,
1989). Some insecticides have been reported to be more efficient in bothknock down
effect and toxicity at lower temperature.
In the fields there are certain factors, which influence the effect of pesticides on
spiders. Some factors are the types of the solvent, soil type, moisture, organic matter and
temperature of time of day of spraying. Further the hunting style, prey preference and
behaviour of spiders also influence their response to pesticide application (Marc et
78
al.,1999). Although pesticides are not ecologically desirable yet they are still most
effective means of combating insect pests. There is some evidence that spiders are less
resistant to insecticides than some insect predators (Toft and Jensen, 1998). Field
application of pesticides often led to reduce diversity of spiders for several weeks (Dinter
and Pöehling, 1992). This decline was due to several factors other than toxicity, such as
disappreance of prey, change in habitat structure and colonization limits (Thomas, 1988).
Some agrobiont spiders, however, recolonize the habitat quickly.
Despite the fact that the wheat aphids seldom cross the economic threshold level
(Nawaz, 2000), the recommendation for insecticide applicationagainst the cereal aphidsby
the agrochemical sector in Pakistan has adversely affected biodiversity and abundance of
spiders natural predator fauna. Aphids are the major insect pests of wheat crop. Confidor
20SL, the first neonicotinoid insecticide, is particularly effective against sucking insect
pests such as aphids whiteflies, several beetles and flies with its systemic and broad-
spectrum activities.It was reported that using confidor against sucking insects is safe for
natural predators of pests including spiders, predatory beetles and bugs (Hough-
Goldstein and Whalen 1993; James, 1997;Kunkel et al., 1999; James and Vogele, 2001;
Elzen, 2001), but other studies reveal that confidor is highly toxic to spiders (Mizell and
Sconyers, 1992; Stark et al., 1995; Delbeke et al., 1997; Sclar et al., 1998; James and
Coyle, 2001).The extensive use of confidor in wheat crop may reducethe diversity,
abundance and efficiency of spiders. Buctril-M is used to control broad leaved weeds of
wheat crop. It is reported that fungicides and weedicides are less effective against the
spiders (Yardin and Edward, 1998).
The application of selective pesticides may prove an important tactic in pest
management programs. Therefore, it is imperative to get information at least on the
susceptibility/resistance of agrobiont spiders species to Confidor (imidacloprid) and
Buctril–M (Bromoxynil+MCPA) in wheat ecosystem. The most abundant spider species
in the wheat ecosystem of Punjab are Lycosa terrestris and Oxyopes javanus.
The aim of present study was to assess the toxicity of confidor and Buctril-M on
both spider species by topical exposure. Along with that toxicity of different days old
residues of both pesticides was also assessed in the laboratory and fields.
79
7.2 MATERIALS AND METHODS
7.2.1 Pesticides
Buctril-M is herbicide used to control broad leaved weeds in wheat crop. It is
inhibitor of photosynthesis at photosystem II and disrupts the plant cell growth. It belongs
to herbicides family Nitrile, Phenoxy carboxylic acid.The field application rate of Buctril
-M is 0.5 liter per acre (1.250 liter per hectare).
Confidor (imidacloprid) belongs to neonicotinoid family of insecticide and as
insecticide replacing organophosphate and carbamate groups. It is a systemic insecticide
used to control variety of soft bodied sucking insect pests of different crops. It acts
through contact and ingestion. Sustained activation of the receptor results from the
inability of acetyl cholinesterase to break down the insecticide. The field application rate
of Confidor is 0.1 liter per acre (0.25 liter per hectare).
7.2.2 Test Organisms
For the study two agrobiont spiders species i.e., Lycosa terrestris and Oxyopes
javanuswereselected..Lycosa terrestris is ground dwelling while Oxyopes javanus foliage
living hunting spiders. All test organisms were collected using sweep net or handy
vacuum (Simens VK 20C) from un-treated fields of wheat crop at Adaptive Research
Farm, Sheikhupura during February through April 2011. Collected specimens were
placed seperately into the collection bottles (10 cm long and 5.5 cm wide) at room
temperature 30+ 5C, relative humidity of 50 + 10% and 12:12 light dark photoperiod.
Each bottle was filled with half an inch thick layer of moist sand to maintain humidity
and mouth was covered with thin cotton cloth. Spiders were fed with different larvae of
insects until used in the different trials. Only the adult males and females were used in
tests.
7.2.3 Topical Exposure
In all bioassays, four concentrations of confidor and buctril-M were topically
applied i.e., field rate, half field rate, one third and one fourthof field rate. Concentrations
less than field rate represented the effect of spray drift on the spiders. Field rate was based
on 100 liter of water spray per acre (250liter per hectare). Dilutions of pesticides were
prepared in water.
80
Prior to pesticide application, spiders were anesthetized by carbon dioxide from a
cylinder supply. A twenty seconds exposure was sufficient to immobilize a batch of ten
spiders for approximately two minutes. By using syringe, one droplet of 0.5 ul of a
pesticides concentration was applied topically on the dorsum of spiders. Control group
was treated only with distilled water. After the application of pesticides, spiders were
placed singly in glass bottles at room temperature and no food was offered during the test.
For each concentration and control 25 individuals were used. Each experiment was
repeated thrice on different days.Spiders were examined at different time intervals till 24
hours after the exposure. The mortality was defined as no movement observed after
stimulation.
7.2.4 Residual Toxicity
To evaluate the toxic effects of residues in the laboratory, wide mouth pots
(diameter) filled with soil collected from the wheat fields weresprayedby pesticide. Each
pot was sprayed either with confidoror buctril-M at concentration of field rate with
knapsack hand sprayer by using insecticides and herbicidal nozzles. To simulate natural
degradation under natural conditions, the pots were kept outside at natural light and dark
period but sheltered from direct sunlight and rain. Control containers were sprayed with
water only. Spiders were released in these pots after 4h or 1, 2, 5, 10 and 20 days of
spray. At each experiment, 20 specimen of a species were used and experiment was
repeated twice. During the tests spiders were not fed. Mortality of spiders due to pesticide
residues was assessed after 24 h by examination of individuals.
7.2.5 Field Assays
Study was conducted from December, 2010 through April,2011in Herdev village
of district Sheikhupura.Twelve wheat plots, one acre each, were randomly selected for the
field assays. Wheat variety ‘Inqilab 91’ was sown through drill during the last week of
November, 2011. Recommended doses of fertilizers (NPK at the rate of 128, 114 and 62
kg per hectare), as approved by the agriculture department, were used in all the fields. Six
plots were randomly selected andon January 9, 2011 sprayed with herbicide buctril-M at
the field rate (500 ml per acre), recommended by manufacturing company using knapsack
hand sprayer. Then on March 9, 2011 herbicide treated plots were sprayed with confidor
at the field rate of 100 ml per acre to control wheat aphids. Control plots were not treated
with any pesticide. However, other inputs such as seed rate, variety, fertilizers and
81
irrigations etc. were kept constant at all sampling plots. All the wheat plots were
harvested in the last week of April, 2011.
Pitfall traps used in the experiment consisted of 250 ml glass jar (6 cm in diameter
and 13 cm in depth). Each trap has 150 ml of 70% ethyle alcohol and few drops of 5%
liquid detergent to lower the surface tension. Sixteen traps were operated in each plot in
four parallel rows. The distance between two rows and in traps within a row was 15
meter.The traps were emptied after 72 h (trapping session) and reinstalled after twelve
days. From foliage, spiderswere collectedby visual search method. From each plot,20
tillers of wheat were selected randomly. These tillers were searched for L. terrestris and
O.javanus thoroughly. Foliage sampling was done at the next day of pitfall traps
installation. Sampling of foliage spiders was commenced on the appearance of spiders
from January 30, 2011 and continued till the harvesting of crop. Collected spiders were
brought to the laboratory and identified to species level.
7.2.6 Statistical Analyses
The percent spider mortality of each species was calculated for both pesticides.
Results obtained from dose response series or time response series after 24 hours were
subjected to Probit Analysis (Lichfield and Wilcoxon, 1949) to determine LD50 and
LT50.).The normality of the field data (log N+1 transformed) was checked using
Kolmogorov–Smirnov test. Field data were subjected to general linear model ANOVA to
estimate the difference in the abundance between treated and control fields, different plots
of the control and treatment and in trapping sessions. Variation in the mortality of both
agrobiont species was assessed using t-test. All statistical analyses were done by using
Minitab package 14.
7.3 RESULTS
7.3.1 Topical Exposure
The susceptibility of spiders against confidor increased both with amount of
insecticide applied and time period in experiments (Figure 7.1). In L. terrestris at
simulated field rate (1ml per l), 75 percent mortality was recorded after 24
hours.However, in O. javanus only 65 percent mortality was recorded for the same
concentration and the dose. The calculated LC50 value for L. terrestris was 0.47(0.43-
82
0.50) ml per liter, approximately half of the field application rate. ForO. javanusLC50
value was 0.62 (0.57- 0.67) ml per liter (Table 7.1). This value also showed that confidor
is highly toxic to both agrobiont species of spiders. The comparison of the susceptibility
of two species against confidor did not show any significant difference from each other
(t=2.61, P=0.08).
Bioassay data of buctril-M (Figure 7.1) revealed low mortaliyin agrobiont species.
However, mortality increases in both species with the increase of the dose. The calculated
LC50 value forL. terrestriswas 15.63 (11.53-18.63) ml per liter, and for O. javanus 20.02
(14.31- 25.71) ml per litre (Table 7.1).These concentrations are much higher than field
application rate. The susceptibility of the studied species did not differ significantly from
each other (P>0.05).
7.3.2 Residual Toxicity
Table 7.2 indicated that the mortality of both spider species declined with the
increase of post sprayed time. In L. terrestris, after 2.65 days of confidor spray, mortality
rate become less than 50 percent. While O. javanus appeared more resistant to the
confidor and its survival rate increase more than 50 percent just after 2.17 days (t=15.65,
P=0.00, Figure 7.2). The residual toxicity of buctril-M was not different for both spider
species (t= 1.75, P=0.154). The mortality rate in both species of spiders, exposed to
residues just after the spray, ranged from 28 to 40 percent, even less than 50 percent
(Figure 7.3).
83
Figure7.1: Response of spiders to different concentrations of pesticides exposed. ■ represent mortality of L. terretris and □ O. javanus to cofidor. Mortality due to Buctril- M was represented by ▲in L. terretris and ∆ in O. javanus. (FR = Field application rate)
0
10
20
30
40
50
60
70
80
control 0.25FR 0.33FR 0.50FR FR
Concentration
per
cen
t M
ort
alit
y
L. t O.J L.t O.j
84
Table7.1: LC50 of confidor and butril-M for the agrobiont spider species
Insecticide/
Species
LC50 ± S.E.
(ml per L) Slope Chi square Probability
Confidor
L. terrestris 0.47 ± 0.04 1.626 0.819 0.664
O. javanus 0.62 ± 0.05 1.473 0.779 0.601
Buctril-M
L. terrestris 15.63 ± 3.60 0.861 1.68 0.43
O. javanus 20.02 ± 5.96 1.07 3.86 0.19
85
Table7.2: LT50 of confidor and butril-M for spider species
Insecticide/
species
LT50 ± S.E.
(days) slope Chi square probability
Confidor
L. terrestris 2.68 ± 0.27 -1.009 2.61 0.623
O. javanus 2.17 ± 0.22 - 0.995 1.45 0.834
Buctril-M
L. terrestris -0.62 ± 0.38 - 0.551 1.46 0.832
O. javanus -1.83 ± 0.67 - 0.452 1.68 0.793
86
0
20
40
60
80
100
120
0 1 3 5 10 20
Days after spray
per
cen
t M
ort
alit
y
1h 4h 8h 16h 24h 48h
A
87
Figure7.2: Laboratory Response of L. terrestris (A) and O. javanus (B) against confidor residues of different age.
0
20
40
60
80
100
120
0 1 3 5 10 20
Days after spray
per
cen
t M
ort
alit
y
1h 4h 8h 16h 24h 48h
0
5
10
15
20
25
30
35
40
45
50
0 1 3 5 10 20
Days after spray
per
cen
t M
ort
alit
y
1h 4h 8h 16h 24h 48h
B
C
88
Figure7.3: Laboratory Response of L. terrestris (A) and O. javanus (B) againstBuctril‐Mresiduesofdifferentage.
0
5
10
15
20
25
30
35
0 1 3 5 10 20
Days after spray
per
cen
t M
ort
alit
y
1h 4h 8h 16h 24h 48h
B
89
Figure7.4: EffectofpesticideontheabundanceofL.terrestrisafterthetreatmentof crop field. Arrow of December represents spray of buctril‐M andMarchofconfidor.
0
10
20
30
40
50
60
12.12 27.12 11.1 26.1 10.2 25.2 12.3 27.3 11.4 26.4
Trapping session
Av
era
ge
nu
mb
er
of
ind
ivid
ua
ls
Control Treated
90
Figure7.5: Effect of pesticide on the abundance of O. javanus after the treatment of crop field. Ist arrow represent spray of buctril-M and 2nd arrow of confidor.
0
2
4
6
8
10
12
14
16
18
12.12 27.12 11.1 26.1 10.2 25.2 12.3 27.3 11.4 26.4
Trapping session
Av
era
ge
nu
mb
er
of
ind
ivid
ua
ls
Control Treated
91
7.3.3 Field Assay
During the study, 2260 individuals ofL. terrestris (707 from treated field and 1553
from control field) were collected from all the 12 plots. However, the abundance of L.
terrestris did not differ in all studies plots (P> 0.05). In contrast to plot type, the density
of L. terrestris was negatively associated with the insecticide spray (F 1,104 = 220.41, P =
0.000). The abundance of L. terrestris(Figure 7.4) also varies with the trapping session (F
9,104 = 42.18, P = 0.000). Paired t test showed that in each trapping session the number of
wolf spider varies in treated and control plots just after the application of insecticides
confidor (t=2.44, P=0.037; Figure 7.4).
A total of 637 individuals of Oxyopes javanus were collected (212 from
treatedand 425 from control) from the studied plots. Results showed significant difference
in the number ofO. Javanusin treated and control plots (F 1,82 = 193.26, P = 0.000) and in
different trapping sessions ( F7, 82= 81.91, P = 0.000). Comparison of each trapping
session of treated and control plots also showed significant difference in the density of O.
javanusafter the application of confidor (t=2.85, P=0.025; Figure 7.5). However, all types
of studied plots were similar to each other.
7.4 DISCUSSION
Spiders have been reported highly sensitive to different insecticides in field and
laboratory conditions (Amalin et al., 2000; Shaw et al., 2006; Marshall, 2006). In our
study susceptibility of agrobiont spiders species (Lycosa terrestris and Oxyopes
javanus)against two pesticides (confidor and buctril-M) was investigated in the laboratory
and field. The pesticides applied at different concentrations on the dorsum of Lycosa
terrestris and Oxyopes javanus. The LC50values of topical exposure showed that confidor
is highly toxic at field rate in the laboratory. Approximately half concentration of field
rate was enough to kill 50% population in the laboratory. Tietjen and Cady, (2007)
reported that toxicity to spiders ranged from less mortality for herbicides to medium
mortality for pyrethroid and organophosphate and to high mortality for cyclo-
compounds.
Spiders are known to be relatively resistant to starvation (Wise, 1993), therefore
individuals in the present experiment were fed to satiated level. However, there may be
still variation in the degree of satiation between experimental animals.Pederson et
92
al.(2002) found that starved Pardosa amentata, or individual fed on low quality prey,
were more susceptible to the effect of dimethoate.
The results of present study showed that residual toxicity ofconfidor was higher
than buctril-M. The post spray exposure showed that reduction in mortality was very
steep in buctril-M than confidor.The difference in mortality may be due to difference in
the interaction of pesticides with the substrate and environment in the field.In the short
term, absorption to soil and volatilization from soil will determine the fate and bio-
degradability of pesticides (Arnold and Briggs, 1990).
Laboratory data showed that for the comparison of field rate, half field rate and
one fourth field rate, confidor was toxic at all concentrations. However, buctril-M was not
toxic at all concentrations.The high mortality in Lycosa terrestris and Oxyopes javanus at
field rate and half field rate of confidor revealed that toxic impacts of this product would
be very high.
Toxicity of confidor was higher than buctril-M in topical and residual toxicity.
The toxicity of weedicide is less for both species. However, imidacloprid was proved
toxic for both species. The susceptibility of both species varies. The susceptibility of
Lycosa terrestris was more compared to the Oxyopes javanus. The difference in the
susceptibility may be due to difference in the insecticide detoxifying enzymes.
Furthermore,Lycosa terrestris is exposed more to the insecticides compared to Oxyopes
javanusas it not only reside on the ground but also spent time on foliage to search prey.
In field experiment, the application of herbicide did not affect the population of
both species. However, the population of both species declined immediately after the
application of confidor. However, recolonization took place just after 15 days. After that
the population of both species again declined due to maturity of wheat crop in April.
LT50 of confidor was more as compared to buctril-M. So confidor exists long time
in the soil.That is why residual toxicity ofconfidor was higher than buctril-M. However,
these different performances of pesticides cannot be transferred to the field situation,
where many other complex environmental factors are also working simultaneously.
However, the current work has urged the need to evaluate the impact of other pesticides,
and the effect of different mode of exposures (topical, residual and ingestion) in order to
gain more realistic information of what may occur in pesticide treated crop.Furthermore,
93
field based assessments are required to provide the most reliable results to be extrapolated
into real environmental situation.
94
Chapter 8
GENERAL DISCUSSION
Variable number of spiders species were recorded from wheatin different parts of
the world. Wu et al. (2009) reported 48 species and Clough et al. (2007) 98 species from
China, Pluess et al. (2008) 94 species from Israel, Toth and Kiss (1999) 149 species from
Hungary.Feber et al. (1998) 56 species from England. Difference in diversity of spiders
was due to presence of study areas in different geographical regions (especially north-
south axis) which led to variable climatic conditions. The present study stretched from
latitude 31° to 33° N.Studies have been reported that local diversity can also be
influenced by microclimate, site fertility, habitat structure, habitat heterogeneity,
elevation, precipitation and biotic interactions (Uetz, 1991; Cornell and Lawton, 1992;
Huston, 1994; Lawton, 1999; Mittelbach et al., 2001 and Whittacker et al., 2001). The
pooled accumulation curve and the ratio of observed to the estimated number of species
suggested that our inventory was 12 to 16 % deficient in different studied plots. However,
additional use of other methods would capture more species.
More than half of spiders captured from the wheat fields were lycosids which
showed a strong preference for wheat habitat. Lycosids are always abundant in close plant
canopy and in irrigated fields (Agnew and Smith, 1989). Higher abundance of lycosids as
compared to other spiders was also noted by Seyfulina (2005) in the wheat fields.
Another possible reason of higher abundance of lycosids in wheat is that the wheat crop
in study area is cultivated after the harvest of rice crop, which is hydrophytic crop and
soil has plenty of residual moisture that favours the lycosids in wheat fields. It is also
reported that activity density and species richness of lycosid spiders were highly
associated with field margins (Öberg, 2007). Wheat fields were divided into small plots
by the dykes in the study area, which were meant to increases the irrigation efficiency but
it also served as refuge for the spiders. These channels have varied type of vegetation,
which provides food, shelter and over-wintering sites for spiders. The strong dominance
of Lycosidae on the ground may partly be attributed to the extensive use of pitfalls as a
sampling method. It has been found that this family is highly susceptible to pitfalls (Lang,
2000).
95
Density and diversity of spiders are closely linked with the structural complexity
of habitat (Rypstraet al., 1999), which is often determined by prey availability (Harwood
et al., 2001) and local agricultural practices (Schmidt et al., 2004). High fertilizer usage
led to high primary production in the high input wheat fields (i.e., BW, TW, ZW and
WW) which attracted more prey population (i.e. aphids and collembolan) as compared to
low input fields (LW). Higher spider density in zero tilled fields (ZW) as compared to
tilled field (WW) might be due to least disturbance and non inversion of soil.Reduced
tilled fields (ZW) also had more structural complexity due to the presence of straw and
trashes which might had provided more retreats and hiding places, untilledfields
hadmoderate temperature and humidity (Rypstra et al., 1999) and support more dipterans
(Wardle, 1995), and more collembolans as compared to tilled fields (Saroj et. al., 2005),
which are important prey for spiders (Settle et al., 1996). Reduced tillage results in more
weeds, more plants residues, less disturbance, higher soil surface moisture (Wardle, 1995)
and proliferation of detritivores(Robertson et al., 1994).Due to these reasonsz zero tilled
fields support more diversity ofspiders including pests and natural enemies (Tonhasca,
1993)
Fields with different edges or living refugia habitat served as refuge for spiders
and can act as a source for dispersal into arable fields, which were frequently disturbed
with different management practices (Lemke and Pöehling, 2002; Schmidt and
Tscharntke, 2005; Öberg and Ekbom, 2006). It also plays a key role in maintaining
biological diversity on farmland (Fry, 1994). The density of spiders in wheat field
surrounded by trifolium (TW) was higher. As the trifolium crop continues till the last
week of May. Moreover, most spiders immigrated into wheat fields because ofmultiple
cuttings and higher frequency of irrigations in trifolium. Plant architecture of trifolium is
dense which makes the microclimate favourable to spiders. Low population of spiders
was recorded from brassica-wheat (BW) as compared to the wheat-wheat fiels., which
was expected due to short span of brassica crop (brassica was harvested in the 2nd week of
March each year).The low population of spiders in brassica field (BW) may be due to the
higher density of aphids infesting brassica crop which serves as food for the spiders and it
restricted the movements of spiders into adjacent wheat fields. The brassica crop requires
less irrigation as compared to trifolium crop; resultantly brassica fields have less moisture
as compared to trifolium. Plant architecture of brassica is open which ultimately affects
the microclimate. The low-input field (LW) showed the lowest density of spiders due to
96
low density of available prey i.e. aphids and collembolans were less as compared to other
habitats. Although, no fertilizer and herbicides was used, as a result there were more
weeds which may provide very complex habitats. But due to no use of fertilizer primary
production was badly affected.
The strip cropping of Brassica napus (intercropping) in wheat crop enhances the
population of the natural enemies and resultantly suppresses the aphid population. In
many studiesit has been reported that strip cropping reduces pest pressure and increases
yield of the main crop (Vandermeer, 1995; Altieri and Nicholls, 1999; Tingey and
Lamont, 1988;Sarker et al., 2007). This finding is in conformity with the results ofPonti
et al. (2007) and Parajulee and Slosser (1999) who reported canola a better trap crop for
enhancing the population of predators.
Negative correlation between grain yield and aphid infestation in the present study
is in accordance with the findings of Tingey and Lamont (1988)whoobserved significant
decrease in yield with the increase ofaphids infestation in the field. The intercropping
creates barrier and causes disruption of host findings for herbivores and could be a
feasible explanation for the low density of aphids in the wheat field (Chabi-Olaye et al.,
2005; Bjorkman et al., 2007). Intercropping substantially improved the crop income over
sole crops but highest return of Rs.151810 was obtained from medium intercropping
followed by (T2) Rs.147756 and lowest return was obtained from large area of strip crop
field Rs.137906. For cost benefit ratio (CBR) medium intercropping produced higher
CBR (1:1.95) than all other treatments. Whereas,our results are in conformity with Khan
et al. (2009) who reported that wheat intercropped with rapeseed produced more returns
than sole wheat. Ali et al. (2009) also reported maximum benefit cost ratio (1.67) and net
profit (Rs.48628/ha) in wheat Brassica intercropping systems. Verma et al. (1997)
reported that intercropping of wheat and Indian mustard gave maximum net return, and
benefit-cost ratio. It is concluded that intercropping of B. napus in wheat helped to
enhance predators’ population in the fields which in turn suppressed aphid population,
thus resulted in natural biological control of aphids. However, low yield of wheat in large
belt of intercrop may be due to more reduction in the area of wheat.
In the laboratory experiment, the three most hunting viz., L.terrestris and Oxyopes
javanus consumed aphids (both nymphs and adults) in more number as compared to other
food items offered in both choice and no choice feeding experiments. Nyffeler and Benz
97
(1982) reported that in agro-ecosystem aphid constituted 25% of the diet of lycosid
spiders.In the study, all species are hunting spiders but L. terrestris, and P. birmanica
(Lycosidae) live on ground andmake burrows in the soil between the crop rowswhileO.
Javanus(Oxyopidae) lives on foliage. In the choice feeding experiment, the number of
aphid killed was low as compared to non-choice feeding experiments. This showed that
availability of high quality prey (larvae of stem borer and armyworm) result in a decrease
in the control of aphids. Some previous studies also reported decrease in the predation of
spiders on the aphids in the presence of alternative prey (Bilde and Toft, 1997; Nyffeler
and Sunderland, 2003), whilesome studied denied it(Sunderland, 1985, 1986; Toft, 2005).
Lycosid spiders preferred mix diets even if single prey types were highly available (Wise,
1993). Consumption of low quality prey depends on the nutritional balance of the spiders.
Those spiders which were nutritionally balanced they consumed three times more aphid
than nutrionally imbalanced spiders (Mayntz and Toft, 2001). Toft (1995) also reported
that hunger level of spider has no effect on the consumption rate of aphid. Female spiders
were voracious predators and consume more insect pests than the males under similar
conditions. Females usually need more energy for oviposition and brood care, while
males need only the essential energy for survival (Kim, 1992). This finding supports the
hypothesis of males as time minimizers and females as energy maximizers (Walker and
Rypstra, 2001). In present study also female of each spider species consumed more prey
as compared to male. The all these three species of spider will reproduce in the coming
month after hibernation, so for them main goal may be to store energy for reproduction.
However, the consumption of prey in the field and laboratory could not be correlated with
each other. In the laboratory, consumption of wheat pests was high as compared to field
data.
The straw refugia within wheat fields resulted in increased population of
arthropods predators. It was also recorded that that the population of aphids decreased
significantly in the straw refugia treatment as compared to control.Our study shows that
the use of straw refugia provides a means for adequately controlling populations of wheat
aphids in wheat crop. Moreover, lesser pest populations occur in plots with straw refugia
as compared to control plots. In field study,Prasifka (2006) reported that the mulches can
be used in IPM along with other agronomic practices. It was reported that the squash bug,
Anasa tristis (DeGeer), and the American palm cixiid, Myndus crudus Van Duzee, were
reported to be favored by the use of organic mulches (Howard and Oropeza, 1998;
98
Cranshaw et al., 2001). The use of organic mulches in other cropping systems has
resulted in a decrease in pest populations. The use of straw mulch has been reported to
increase the abundance of predators in the field, which in turn reduces pest populations
(Halaj et al., 2000).
The availability of alternative preys enhances the predator activity density in
agroecosystems (Settle et al., 1996, Wise et al., 1999). It is also reported that the
generalist predators are absolutely dependent on the physical structure of their
environment (Chiverton and Sotherton, 1991; Uetz, 1991; Ramzan (2002); Salim et al.,
2003) reported higher density of spider as compared to staphylinids (Rove beetles). It
may be attributed due to higher moisture level and humid microclimate in refugia
(Basedow, 1994).Rove beetles are reported to be polyphagous and their food on ground
ranges from algae, fungi, collombolans and decaying organic matter (Good and Giller,
1991). A significant difference was observed for abundance of coccinellids between the
treatments. It may be due to reason that these predators reside mainly on foliage and not
on the ground. As we have used only pitfall traps to capture predators and part of
coccinellids present on the ground were exposed to that traps. The population of aphids
also decreased significantly in the straw refugia treatment as compared to control. But it
is fact that the population of aphid crosses the ETL in both the treatments in the mid of
March each year. Several studies have shown relation between the use of mulch and a
decrease in pest populations (Wise et al., 1999; Way and Khoo, 1992; Sunderland and
Samu, 2000).
The susceptibilityof agrobiont spiders species (Lycosa terrestris and Oxyopes
javanus)against two pesticides (confidor and buctril-M) was investigated in the laboratory
and field. The pesticides applied at different concentrations on the dorsum of Lycosa
terrestris and Oxyopes javanus. The calculated LD50 values showed that Lycosa
terrestris ishighlysusceptible to confidor as compared to buctril-M. Similarly, confidor
was found highly toxic to the Lycosa terrestris and Oxyopes javanus in the field study.
The population of both species declined steeply after the application of confidor on wheat
crop. Spiders have been reported highly sensitive to different insecticides in field and
laboratory (Amalin et al., 2000; Shaw et al., 2006; Marshall, 2006).
Non-significant difference in susceptibility of male and female in present study
may be due to high morality in shorttime by confidor.Due to this mortality difference in
99
susceptibility cannot be established. The laboratory data of present study confirm that
susceptibility of Lycosa terrestris and Oxyopes javanus to both pesticides is sex
related.Male usually have high susceptibility than females. Number of authors also
reported difference in susceptibility for both sexes (Dinter and Pöehling, 1995; Dinter,
1997).
The results of present study showed that residual toxicity of confidor was higher
than buctril-M. The post spray exposure showed that reduction in mortality was very
steep in buctril-M than confidor.From the laboratory data the comparison of field rate,
half field rate and one fourth field rate showed that confidor was toxic at all
concentrations. However, buctril-M was not toxic at all concentrations.
RECOMMENDATIONS:
1) Farm and field boundaries and irrigation channels serve as breeding and over-
wintering sites for the spiders; these should neither be disturbed nor sprayed to
control weeds.
2) Crop diversity at farm and agriculture landscape level favours the predator
population and helps to suppress pest population.
3) Zero tillage and minimum disturbance of soil is favourable to predators.
4) Refugia either present at edge or in the field help to increase the density and
diversity of spiders.
5) Use of balanced fertilizers enhances the population of predators and pests.
6) Intercropping of brassica (Canola) in the centre of wheat field attracts predators
and these predators ultimately suppress pest population in wheat crop. It also
enhances the cost benefit ratio than sole wheat crop.
7) Refugia, straw and previous crop stubbles serve as shelter for the predators and
enhance suppression of pests.
8) Even the insecticides thought as safer, are toxic to spiders, therefore the
process of sorting the safer insecticides be continued in future.
100
Chapter 9
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