Manipulation of Tritrophic Interactions for IPM

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Manipulation of Tritrophic Interactions for IPM
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Tri-trophic Interaction
Predator/parasitoids
Herbivores
Plants
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Plants Interact With the Third Trophic Level
Chemically Morphologically
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Multi-trophic interactions
Hyperparasitoid
Predator/parasitoids
Herbivores
Plants
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The Slow Growth High Mortality Hypothesis
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• Feeding on sub-optimal food produces an increase
  in insect herbivore developmental time.

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• Increased developmental time in herbivores may
  increase vulnerability to natural enemies

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The Slow-Growth-High-Mortality Hypothesis

• Prolonged larval development of herbivores
  results in greater vulnerability and thus greater
  mortality due to natural enemies.
• (Clancy and Price 1987).

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Tests Have Produced Mixed Results

• Support
• - Free feeding herbivores.
• - Feeding on same or related plant species.
• Fail
• - Concealed feeding herbivores.
• - Feeding on unrelated plant species.

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Studies Supporting the Hypothesis

G.lineola
- Develop longer on S.sasyclados
- Predators attack more on S.dasyclados
P.rapae
- Develop longer on low N collards
- Predators attack more on low N collards
M.disstria
- Develop longer on late budbreaks
- Predators attack more on late budtbreaks
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Which Natural Enemies Have Been Considered to
Test the Hypothesis?

• Suite of predators.
• Single parasitoid species.
• Parasitoid community.

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Orgyia leucostigma
Acer negundo
Salix nigra
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Experimental Protocol

• Rear O. leucostigma on willow and box elder.
• Measure development time and adult mass on willow
  and box elder.
• Use 7-year data base to determine percent
  parasitism of O.leucostigma on willow and box
  elder.

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O. leucostigma developed faster on willow
Plt0.0001
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Female O.leucostigma on willow were heavier than
on box elder.
b
c
F
F
a
a
M
M
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Percent Parasitism of O.leucostigma on two tree
species
Overall percent parasitism on
Family
Parasitoid species
Box elder
Willow
1. X2 11.83 Plt0.001
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In Summary

• O. leucostigma developed faster in willow than in
  box elder.
• Overall parasitism in O.leucostigma was greater
  in willow than in box elder.

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Conclusion

• The slow-growth-high-mortality hypothesis does
  not hold for O. leucostigma and its parasitoid
  community.

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Conclusion

• On a free feeding herbivore feeding on unrelated
  species.
• Support
• - One parasitoid species considered.
• Fail
• - A community of parasitoids considered.

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Conclusion

• The effect of host plant quality on individual
  species of natural enemies might differ
  significantly from the effect of host plant
  quality on the natural enemy community.

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Differential susceptibility of herbivores to
natural enemies
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