Patch‐leaving rules for parasitoids with imperfect host discrimination

Abstract

Abstract. The solitary parasitoid Anagrus delicatus attacks hosts (plant‐hopper eggs) that exist in distinct batches and that are readily detectable to the foraging parasitoid. However, Anagrus delicatus attacks only a small fraction of the available hosts within a batch of eggs and then disperses (Cronin & Strong, 1993a). Here we address the question: Why is A.delicatus abandoning seemingly high quality patches? A parasitoid with an imperfect ability to discriminate between unparasitized hosts and hosts that it has attacked earlier within the same patch experiences a risk of self‐superparasitism when attacking multiple hosts within a single patch. Self‐superparasitism can incur costs in the form of lost time and eggs. Early patch leaving can be favoured as a means of avoiding the costs of self‐superparasitism. A simple static model demonstrates that patch leaving is favoured by low costs of travelling to a new patch, high error rates in discriminating previously self‐parasitized hosts, and high levels of parasitism in the currently occupied patch. A more detailed dynamic state variable model, parameterized for A.delicatus, demonstrates that this parasitoid's seemingly enigmatic behaviour can be explained under our hypothesis. In order for this to be the case, we predicted that A.delicatus cannot recognize previously parasitized hosts. Subsequent to our prediction, Cronin & Strong (1993b) demonstrated that experienced A.delicatus do not avoid ovipositing in previously self‐parasitized hosts. Optimal patch leaving rules can be highly sensitive to even very low host discrimination error rates, which may be widespread among parasitoids.