PATCH-LEAVING RULES FOR PARASITOIDS WITH IMPERFECT HOST DISCRIMINATION

1. The solitary parasitoid Anagrus delicatus attacks hosts (planthoppe r 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? 2. A paras itoid with an imperfect ability to discriminate between unparasitized hosts and hosts that it has attacked earlier within the same patch exp eriences a risk of self-superparasitism when attacking multiple hosts within a single patch. Self-superparasitism can incur costs in the for m of lost time and eggs. Early patch leaving can be favoured as a mean s of avoiding the costs of self-superparasitism. 3. A simple static mo del demonstrates that patch leaving is favoured by low costs of travel ling to a new patch, high error rates in discriminating previously sel f-parasitized hosts, and high levels of parasitism in the currently oc cupied patch. 4. A more detailed dynamic state variable model, paramet erized for A. delicatus, demonstrates that this parasitoid's seemingly enigmatic behaviour can be explained under our hypothesis. In order f or 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. 5. Optimal patch lea ving rules can be highly sensitive to even very low host discriminatio n error rates, which may be widespread among parasitoids.