Discrimination of parasitized aphids by a hoverfly predator: effects on larval performance, foraging, and oviposition behavior

The choice of oviposition site by female aphidophagous predators is crucial for offspring performance, especially in hoverflies whose newly hatched larvae are unable to move over large distance. Predator and parasitoid interactions within the aphidophagous guild are likely to be very important in influencing the choices made by predatory hoverfly females. In the present study, the foraging and oviposition behavior of the aphidophagous hoverfly Episyrphus balteatus DeGeer (Diptera: Syrphidae) was investigated with respect to the parasitized state of its aphid prey, Acyrthosiphon pisum Harris (Homoptera: Aphididae), that were parasitized by Aphidius ervi Haliday (Hymenoptera: Aphidiidae). We also recorded the number of eggs laid by hoverfly females when subjected to parasitized aphids. Furthermore, we studied the influence of being fed with parasitized aphids on hoverfly larval performance. Hoverfly females did not exhibit any preference for plants infested with unparasitized or aphids parasitized for 7 days. On the other hand, plants infested with mummies or exuvia were less attractive for E. balteatus. These results were correlated with (i) the number of eggs laid by E. balteatus females and (ii) larval performance. Thus, our results demonstrate that E. balteatus behavior is affected by parasitoid presence through their exploitation of aphid colonies. Indeed, hoverfly predators select their prey according to the developmental state of the parasitoid larvae.