First in, last out: asymmetric competition influences patch exploitation of a parasitoid

Parasitoid females exploiting a patchy environment may encounter conspecifics on the host patches they visit or arrive in patches where other females have already parasitized hosts. When 2 or more foragers with differential arrivals exploit a resource patch simultaneously, the solution for the evolutionary stable patch residence times is the outcome of an asymmetric war of attrition. A theoretical prediction is that the forager that arrives first should stay longer than those arriving later, as a result of a resource value asymmetry. This study aims to examine how the arrival order on a host patch affects patch time in the solitary aphid parasitoid Aphidius ervi. For this purpose, 3 situations of competition were tested: single individuals foraging on unexploited patches (no competition), individuals foraging on previously exploited patches, and individuals exploiting patches in the presence of a competitor. Our data confirm the theoretical prediction: first-arriving females stay longer on a patch of hosts than second-arriving females. Neither host rejections nor host attacks affect patch-leaving decisions of females, but foraging with a competitor and previous encounters with a competitor increase the patch residence time of first-arriving females. This experiment is the first to test the effect of arrival order on patch exploitation strategies in nonfighting species.