Small but smart: the interaction between environmental cues and internal state modulates host-patch exploitation in a parasitic wasp

The reproductive success of insect parasitoids depends on two activities, searching for hosts to obtain immediate fitness rewards (offspring) and searching for food to extend life span and enhance future reproductive opportunities. Models suggest that to deal with this trade-off and to cope with the variability of the resources they depend on, parasitoids should simultaneously integrate information originating from three distinct sources: host and food availabilities in the environment (environmental information) and the metabolic reserves of the parasitoid (internal information). We tested whether, in the parasitic wasp Venturia canescens, these three types of information are perceived simultaneously and interact during host-patch exploitation. Experiments were performed with strains originating from two different geographical locations and with individuals of the two reproductive modes, arrhenotoky and thelytoky. We hypothesised that there would be differences between modes of reproduction as they thrive in different ecological conditions. Our results show that metabolic state, food availability and the number of ovipositions performed simultaneously modulate patch residence time in V. canescens of both populations and reproductive modes. Unfed wasps left their host patch earlier than fed ones. The tendency to leave the patch increased with an increasing probability of finding food. Our study confirms that globally, each oviposition increases the patch-leaving tendency (decremental mechanism). This effect was modulated by both the metabolic reserves and food availability, and the relationship depended on the geographic origin of populations. Individuals of one of the populations switched from a decremental to an incremental patch-leaving mechanism depending on the presence or absence of food in the vicinity. Differences between reproductive modes in the responses to environmental cues can be explained by the different ecological conditions they live in.