How could host discrimination abilities influence the structure of a parasitoid community?

Abstract

AbstractThree relatedAphidiusparasitoid species share the same host, the grain aphidSitobion avenae. Among this parasitoid community,Aphidius rhopalosiphiis the most abundant species in the field. Both the interspecific host discrimination ofA. rhopalosiphitowards hosts parasitized by the two other species (i.e.A. avenaeandA. ervi) and the interspecific host discrimination of the two other species towards hosts parasitized byA. rhopalosiphiwere studied here. Results showed that females ofA. rhopalosiphiandA. avenaeboth discriminated between unparasitized hosts and hosts parasitized by the other species. This discrimination occurred only after ovipositor insertion, suggesting the perception of an internal marker of parasitism. Likewise, females ofA. rhopalosiphiandA. erviwere able to discriminate between unparasitized hosts and hosts parasitized by the other species. However, in this combination of species, recognition of parasitized hosts occurred before ovipositor insertion, through an antennal perception, suggesting the presence an external cue indicating parasitism. Hence, interspecific host discrimination in the threeAphidiusspecies is based on internal or external cues, which are used either alone or together. Our results showed that the cues used for interspecific host discrimination depend on the specific identity of the interaction. These differences seemed strongly linked to the way the different species respond to defensive behaviours of their aphid hosts. Results are discussed in the context of optimal foraging and possible consequences for community structure.