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Published on: August 31, 2018
EVOLUTION OF AN APHID-PARASITOID INTERACTION: VARIATION IN RESISTANCE TO PARASITISM AMONG APHID POPULATIONS
1Department of Entomology, Section of Ecology and Systematics, Corson Hall, Cornell University, Ithaca, New York, 14853.
Pea aphid populations specialized on alfalfa show greater resistance to parasitoid wasps than those on clover. This genetically based resistance, not influenced by host plants or behavior, suggests limited evolution of resistance in clover-specialized aphids.
Area of Science:
- Ecology
- Evolutionary Biology
- Entomology
Background:
- Herbivore-parasitoid interactions are influenced by herbivore-plant relationships.
- Host plant specialization can lead to genetic differentiation in herbivore populations.
- This differentiation may impact traits related to parasitoid interactions.
Purpose of the Study:
- To investigate how genetic differentiation of pea aphid (Acyrthosiphon pisum) populations on different host plants affects their interaction with the parasitoid wasp (Aphidius ervi).
- To determine if resistance to parasitism is genetically based and influenced by host plant specialization.
Main Methods:
- Comparative parasitism assays exposing aphids from alfalfa and clover to parasitoids from both crops.
- Controlled experiments to isolate physiological resistance from behavioral factors.
- Clonal replication on host and common plants to assess nutritional/chemical effects.
- Genetic variation assays for resistance within clover aphid populations.
Main Results:
- Alfalfa-specialized pea aphids exhibited significantly lower parasitism rates compared to clover-specialized aphids, irrespective of parasitoid origin.
- Physiological resistance, not aphid or wasp behavior, accounted for the difference in parasitism.
- Resistance patterns persisted when aphids were reared on a common host plant, indicating a genetic basis.
- Limited genetic variation in resistance was found in clover aphid populations, contrasting with higher variation in alfalfa populations.
Conclusions:
- Genetic differentiation driven by host plant specialization in pea aphids results in differential resistance to parasitoids.
- Physiological resistance is a key factor, with a strong genetic component.
- Low genetic variation for resistance in clover-adapted populations may impede their evolutionary response to parasitoid pressure.
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