Mechanisms of species‐sorting: effect of habitat occupancy on aphids' host plant selection

Interspecific interactions such as competition are important factors affecting insect herbivore fitness. Host choice in herbivorous insects including aphids has largely been studied with respect to host plant condition, while the role of competition is also very important. Tansy (Tanacetum vulgare L.) hosts three specialised aphids, Macrosiphoniella tanacetaria (Kaltenbach), Metopeurum fuscoviride Stroyan and Uroleucon tanaceti (L.) (Hemiptera: Aphididae). In this study, a set of greenhouse and field experiments were carried out to investigate whether aphid host plant choice was affected by the presence of the other aphid species. When winged individuals were given the choice between unoccupied plants and plants occupied by the same or another aphid species, choices generally reflected the outcome of competitive interactions among aphids. Colonisation of plants by winged individuals was influenced not only by the presence of other aphids on the host plant but also by previous infestation. The host choice of winged individuals basically reflected competitive hierarchies, i.e. aphids in most cases selected plants where future competition was less likely. By contrast, unwinged aphids did not show any host plant preference. For M. tanacetaria previously infested plants promoted the production of winged offspring. Our results show that competitive interactions could affect host selection behaviour by aphids. In a metacommunity context, such preferences in colonising different habitats leads to species‐sorting through habitat heterogeneity.