gastropod attractants: potential management tool for giant african land snail lissachatina fulica?...
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Gastropod attractants: Potential management tool for
Giant African Land Snail Lissachatina fulica?
RESEARCH UPDATE
Rory McDonnell1, Amy Roda2 and Jocelyn Millar1
1: Department of Entomology, University of California, Riverside
2: CPHST, USDA-APHIS, Subtropical Horticultural Research Station, Miami
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Background
Chemical cues play roles in feeding, prey detection, predator avoidance, alarm responses, species recognition & reproduction in gastropods
External attractants e.g. from food sources
Possible pheromones– Sex pheromones– Aggregation pheromones
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Sex pheromones
Photo: Wikimedia Commons
• Spawning and breeding in mud snails organized by at least two kairomones and three pheromones
• Gland in the head produces a pheromone that elicits courtship and copulation
Ilyanassa obsoleta Euhadra peliompha
exoticsguide.org
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Aggregation Pheromones
Lissachatina oriented towards odor of conspecifics
Source reported to be the pedal mucus gland
Attractant is a pheromone
Source: Chase (1978)
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Why no further work to follow up?
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Our Approach
1. Attractants produced by conspecifics Follow up on preliminary work by Chase from
1978, showing attraction of GAS to odors from conspecifics
2. Attractants from other sources
Identify and develop attractants from other sources (e.g., food)
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1. Pheromones
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Response of Lissachatina fulica to the odor of conspecifics
X2 = 24.69, P<0.001, n=20
78%
22%
Treatment ArmControl Arm
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Aeration chamber for collecting odors from live snails
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Odor analysis resultsLittle difference between snail and control aerations
One compound appeared consistently in snail odor collections
2-diethylaminoethanol
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Response of Lissachatina fulica to a 0.01% solution of 2-diethlyaminoethanol
X2 = 6.14, P<0.05, n = 14
64%
14%
21%
Treatment ArmControl ArmNo Choice
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2. Other attractants
Fed snails a variety of different foods
With one food item, noticed a distinct oriented mass movement towards the food
Much more pronounced than normal, clearly strong attraction to odors from the food
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Attraction to food odors
• Pronounced oriented movement towards food source
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Replicated bioassays• Two choice bioassay
• 1ml of treatment and 1ml control on filter paper
• Position of treatment and control switched after each replicate
• Snails tested individually to prevent trail-following
• Choice made when snail touched the Petri dish or after 45min
Treatment
Control
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Response to steam distillate
70%
10%
20%
Steam distillateControl (water)No Choice
X2 = 6.07, P<0.05, n = 10
Statistically significant attraction
Result: Attractants are extractable and heat stable
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Response to ether extract of steam distillate
X2 = 6.07, P<0.05, n = 10
Statistically significant attraction
70%
20%
10%
Ether extract
Control (ether)
No Choice
Result: Attractant extractable into organic solvent, easier to work with
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Response to acid-treated steam distillate
X2 =6.00, P<0.05, n = 10
Statistically significant attraction
Result: Attractant cannot be amine or other organic base
67%
33%
Acid-treatedControl (water)No Choice
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Response to base-treated steam distillate
X2 = 7.00, P<0.05, n = 10
Statistically significant attraction
Result: Attractant cannot be organic acid
83%
17%
Base-treated
Control (water)
No Choice
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Response to neutralized ether extract of steam distillate
X2 = 20.20, P<0.001, n = 10
Statistically significant attraction
100%
Neutralised extractControl (ether)No Choice
Result: Attractant is one or more neutral compounds in the steam distillate
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Response to methanol elution of steam distillate volatiles trapped on solid phase extraction cartridge
X2 = 8.32, P<0.05, n = 10
Statistically significant attraction
Result: Attractant is a moderately polar compound
75%
25%
Neutralised extract
Control
No Choice
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Conclusion
The attractant is a heat-stable neutral compound(s) that is moderately polar
Some attraction to a partial reconstruction of the compounds in the neutrals fraction
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Next steps!Pheromone:1. Continue to analyze the aeration extracts
2. Testing of pedal mucus gland
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Next steps!
Food based attractant:
1. Analysis of the neutrals fraction from the steam distillate
2. Development of a fractionation scheme
3. Reconstruction of the volatiles blend for bioassays
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Questions?
Acknowledgements: APHIS-PPQ-CPHST for funding to date