Indirect interactions in aphid-parasitoid communities

Indirect interactions between populations of different species can be impor tant in structuring natural communities. Indirect effects are either mediat ed by changes in population densities (trophic or density-mediated effects) or by changes in the behavior of species that are not trophically connecte d (behavioral or trait-mediated effects). We reviewed the literature on aph ids and their parasitoids to explore the various possible indirect interact ions that can occur in such communities. The review was motivated by our st udy of a particular aphid-parasitoid community in a natural (i.e., nonagric ultural) habitat, and by the wealth of information that exists about aphid- parasitoid systems in agricultural settings. We focused our review on aphid -parasitoid interactions, but considered how these were influenced by the o ther aphid natural enemies and also by aphid mutualists and host plants. We conclude that indirect effects are likely to have a major effect in struct uring aphid-parasitoid communities, and that the latter are a valuable mode l system for testing ideas about community interactions.