9700696 ROOT The role of population differentiation in the evolution of species interactions is not well documented. Selection can differ by population, leading to coevolutionary interactions in some areas and non reciprocal evolution in other areas. The pea aphid, a pest of legume crops, is attacked by the parasitoid, Aphidius ervi. Pea aphids in New York which specialize on alfalfa are two or three times more resistant to parasitism than pea aphids specialized on clover. Resistance is genetically determined and physiologically based. It is not a product of host-plant induced effects or either insect species on the two crops. The proposed research focuses on three areas. 1) A survey of pea aphids on both crops from two other geographical area, Maryland and France, will indicate the generality of the observed pattern of relative resistance. 2) Reciprocal transplant experiments in the lab will determine whether the insects are locally adapted within their geographic region. 3) An experiment will be performed to ascertain the relative magnitude of genetic variation for resistance in pea aphids from clover and from alfalfa. This will indicate if lower levels of genetic variation in clover could be slowing the evolution of resistance despite strong selection in both crops. This research is important in enhancing a basic understanding of the evolution of species interactions, and will provide insight in the effects of the evolution of species interactions on the efficacy of biological control programs.
