biological control of pest snails in australia, · pdf filejune 14, 2011 wwppg seminar session...

June 14, 2011

WWPPG seminar session 1 by Aisuo Wang 1

Biological control of pest snails in Australia using native nematodes

Background

Four major pest species of snails in Australia

Introduced from Mediterranean area almost one century ago Theba pisana

(white Italian snail or sand dun snail)

Cochlicella barbara(conical or pointed snail)

Cochlicella acuta(small conical or pointed snail )

Cernuella virgata(vineyard snail or common white

snail )2

Summer(Dec. to Feb)(Dec. to Feb)

Autumn(Mar. to May)

Spring(Sep. to Nov.)

Winter(June to Aug.)

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June 14, 2011


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Current control strategies for snails

stubblestubble management over summer (grazing, rolling, slashing)

burning baiting

windrowing header modifications

post harvest grain cleaning

biological control (parasitic fly)

concerns with health and

environmental issues

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Current status of Biological Control of Mediterranean Snails in Australia

Parasitoid fliesParasitoid flies

Sarcophaga uncicurva and S. balanina•For C. vigata and T. pisana•Host range too wide

Sarcophaga penicillataSarcophaga penicillata•For C. virgata•Released at 20 sites on the Yorke Peninsula•10% establishment• Spread one km over a two year period

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Current status of Biological Control of Mediterranean Snails in Australia

Attempts in 1990s found six nematode isolates able to parasitise C. virgata, T.

pisana and C.

Rhabditidnematode R954 was found to be

best.

Field trials inconclusive due to adverse

weather

acuta

Charwat et al. (2000). Biocon Sci & Tech 10, 147‐1558

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Field collections of snails

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Laboratory culture of snails

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Collection of nematode isolates

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New South WalesSouth Australia

Wagga Wagga

Victoria

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Isolation from larvae and snails

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h

PRIMARY PATHOGENICITY TESTS

Screening the promising nematode strains

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Pathogenicity Testing

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Summary of Pathogenicity Tests

I l N113 N212 N431Isolates N113, N212, N431, N432 and N622 killed C.

virgata

Isolate N512 killed C. barbara

Nematodes were recovered from all

cadavers

Further testing showed isolate N431 killed all 4

snail species in 4 to 8 days

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June 14, 2011


Pathogenicity test for nematode isolates against pest snail of C. virgata under laboratory conditions

Isolate Density Species Reps Time Mortality Recovery

N431

500

500

500

500

C. barbara

T. pisana

C. virgata

C. acuta

2

2

4

2

8 d

8 d

8 d

8 d

100%

100%

100%

100%

+++

+++

+++

++

400 C barbara 4 8 d 75% +++

N512

400

400

400

400

C. barbara

T. pisana

C. virgata

C. acuta

4

4

4

4

8 d

8 d

8 d

8 d

75%

0%

0%

0%

+++

‐

‐

‐

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Pathogenicity test for nematode isolate N431 against pest snail of C. virgata under field‐like conditions

Isolate Density Species Reps Time Mortality Cadaver

N431

600

1300

C. virgata

C. virgata

10

10

8 d

8 d

30%

60%

++

+++

Control Water C. virgata 10 8 d 10%‐

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b f l l h l l h

NEMATODE IDENTIFICATION

A combination of molecular and morphological approaches

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Identification of Nematodes

Morphology using Light and Scanning Electron

Microscopy

Sequencing of the 18S ribosomal RNA gene of the nematodes isolated with primers • SSU18A/SSU26R and• SSU18A/SSU26R and• RHAB1350F/RHAB1868R.

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Light Microscopy

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Morphology of Nematodes (SEM)

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b f l l h l l h

BACTERIAL IDENTIFICATION

A combination of molecular and morphological approaches

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Identification of bacterial isolates

A total of 31 bacteria were isolated from the bodies of four promising nematode

isolates.

The identification of these bacteria isolates was conducted by both fatty acid analysis and DNA barcoding (with two different primers: 0008F/0532R andprimers: 0008F/0532R and

341F/534R).

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FURTHER PATHOGENICITY TESTS

Nematode/Bacterial Interactions

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Pathogenicity test with different nematode/bacteria combinations against C. virgata

Figure : Pathogenicity test with different nematode/bacteria combinations against C. virgata (1#‐‐‐‐‐4711B6; 2#‐‐‐‐‐0431B1; Dark columns‐‐‐‐‐4711B6 involved nematode/bacteria combinations; light columns‐‐‐‐‐0431B1 involved nematode/bacteria combinations)

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Pathogenicity test with different nematode/bacteria combinations against C. barbara

Figure : Pathogenicity tests against large and small C. barbarawith nematode/bacteria combinations involved bacterium 4711B6. D: 4711B6; 1 and 2: large and small snails.

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June 14, 2011


Pathogenicity test with different nematode/bacteria combinations against C. barbara

Figure : Pathogenicity tests against large and small C. barbara with nematode/bacterial combinations involved bacterium 0431B1. B: 0431B1; 1 and 2: large and small snails.

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SOME POINTS

N4711 + 4711B6 andN0431 + 0431B1 , caused significantly higher snail mortality

over other nematode/bacteria combinations (P <

4711B6 or 0431B1related

nematode/bacterial combinations also caused higher snail mortality among C.

It appears that large C. barbara are more sensitive to the attack

of nematode/bacterial combinations than0.001) against C.

virgata.barbara. combinations than

small C. barbara

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PATHOGENICITY OF OTHER ORGANISMS

Earthworms

Slugs

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Earthworm Pathogenicity tests

Nematode/bacteriDensity (per ml) Earthworm size Repetition Days

Earthworm a combinations

Density (per ml) Earthworm size Repetition Daysmortality (%)

N0431 + 4711B6 2333 Large or small 8 14 0

N4711 + 4711B6 2056 Large or small 8 14 0

N3814 + 4711B6 1722 Large or small 8 14 0

N4712 + 4711B6 3722 Large or small 8 14 0

N0431 + 0431B1 3333 Large or small 8 14 0

N4711 + 0431B1 4056 Large or small 8 14 0

N3814 + 0431B1 1268 Large or small 8 14 0

N4712 + 0431B1 1556 Large 8 14 0

Negative control 0 Large 8 14 0

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June 14, 2011


Slug Pathogenicity tests

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Pathogenicity on slugs

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Pathogenicity on slugs

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FIELD TRIALSOptions to be considered currently

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Factors affecting the field trials

Snails’ needs Nematodes’ needs

Food Shading Temperature Oxygen Moisture

Moisture

Temperature Density No UV Oxygen Hosts

To ensure the success of field trials

Suitable locations for field trials (natural

conditions)

Nice moisture of the soil

Right temperature of the soil

Right nematode strains

Enough density of nematodes

Right percentage of infective juveniles in

total nematode populations

Right formulation

of nematodes

Enough contact between nematodes and snails

Good management of the field

trials

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Case study: field trial in 2010

Lessons we got

The snail enclosures made with steel could not efficiently enclosesnails. At the end of the trial, the total snail

number (including both dead and alive ones) in each enclosure could

The size of the snail cage (33 cm x 33 cm) is too small to prevent snails from moving out of the

The design of the snail enclosures actually encourage snails to

escape from nematodes’ attack by

not match the original data. More surprisingly, foreign snails were found in some enclosures.

gboundaries.

ycrawling up to the top

of the cages.

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1st option for future field trials

Major points

Expand the plot area (say 10 m x 10 m) so that snails cannot

Use suitable tool (such as plastic screen) to

immobilize snails

Use suitable materials (such as timber) to hold down the screen firmly and thusmove out of the

boundaries easily within the test

areafirmly, and thus prevent snail from

escaping

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June 14, 2011


Weights to hold down the screen

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2nd option for future field trials

Major points

Set up a barrier area (wide enough) with nematodes to separate pest snails

Use snail attractants to lure pest snails crossing over

Examine the reactions of snails when they have l d

p pfrom materials to be protected

crossing over the nematodes

barrier

crawled across the nematode

barriers

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Nematode bait areaPest snails area

Snail attractants area

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biological control of pest snails in australia, · pdf filejune 14, 2011 wwppg seminar session...

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