Foraging behaviour by parasitoids in multiherbivore communities

Parasitoid foraging decisions are often affected by community characteristics such as community diversity and complexity. As part of a complex habitat, the presence of unsuitable hosts may affect foraging behaviour of parasitoids. First, unsuitable herbivores may affect the localization of patches where hosts are present. Second, encounters with unsuitable herbivores in the food plant patch may affect parasitoid decisions during their searching behaviour in the patch. In this review, we outline the importance of the presence of unsuitable herbivores on the behavioural responses of parasitoids during both these foraging phases. Nonhosts feeding on a neighbouring plant or on the same plant individual the host is feeding from may affect odour-based searching by parasitoids in a way specific for the species combination studied. Feeding by specific host and nonhost-herbivore combinations may induce volatiles that are more, less or equally attractive compared to those from plants infested by the host only. Within the food patch, mixed presence of host and nonhost may reduce the number of hosts parasitized per time unit and reduce parasitoid foraging efficiency. Importantly, we show that a single nonhost species may have contrasting effects in terms of its effects on odour-based searching and patch residence decisions. We conclude that studying host searching behaviour at both phases of foraging is essential for our understanding of parasitoid foraging behaviour in natural and agricultural settings. We further speculate on the ecological context in which unsuitable herbivores affect either of the two phases of parasitoid foraging.