Early experience influences several steps of the host selection process differentially in Aphidius ervi (Hymenoptera, Braconidae)

Experience of host-associated olfactory stimuli during development affects subsequent foraging decisions in many parasitoids, leading to host fidelity. We have recently shown that odours emitted by an alien host-plant complex (HPC) may affect this learning process. However, the consequences of this olfactory experience on parasitoid host foraging decisions is unknown. Here, we investigated if olfactory preferences induced by experience might drive parasitoid HPC choice and oviposition decisions. We presented two HPCs in dual choice experiments to Aphidius ervi females that had been reared on each HPC, either in a simple (one HPC) or complex (two HPCs) olfactory environment. HPC choice, time before landing on a HPC and number of aphid attacks were recorded. Early experience had contrasting effects on each of these parameters. Regardless of their origin, parasitoids did not land preferentially on any HPC, but they more frequently attacked one of the two hosts (Acyrthosiphon pisum) once they had landed on its HPC. Females emerging from the A. pisum/faba bean HPC attacked more aphids, regardless of the host species. Finally, the olfactory complexity of the environment had inconsistent effects on foraging decisions. These observations, contrasting with previous results obtained in olfactometer assays, indicate that olfactory preferences induced in early stages are not sufficient to predict parasitoid oviposition decisions. Moreover, the integration of multiple signals at several scales might generate different foraging patterns at each step of the host selection process.