Segoli, M., Department of Entomology, University of California, Davis, CA, United States
Keasar, T., Department of Science Education-Biology, University of Haifa, Oranim, Mobile Post Tivon, Israel
Bouskila, A., Department of Entomology, University of California, Davis, CA, United States
Harari, A.R., Department of Entomology, University of California, Davis, CA, United States, Department of Entomology, Agricultural Research Organization, The Volcani Center, Bet Dagan, Israel

Female parasitoids often reject hosts of poor quality, where the survival and fitness of their offspring are expected to be low. In polyembryonic parasitoid wasps, a clone of genetically identical embryos develops from one egg in a host. In the wasp Copidosoma koehleri, each female clone produces one soldier larva that attacks competing clones inside the host. Aggression by soldiers is directed usually towards unrelated clones. Accordingly, it may be predicted that females will prefer nonparasitized over parasitized hosts, especially if the latter have been parasitized previously by a mated unrelated female, as a result of the reduced chances of survival for their offspring inside these hosts. In accordance with these predictions, females prefer nonparasitized hosts over self-parasitized hosts when they are presented simultaneously. By contrast to the predictions, females prefer hosts parasitized by an unrelated conspecific over nonparasitized hosts when presented simultaneously. Females do not distinguish hosts parasitized by conspecifics from self-parasitized hosts when presented simultaneously. They reject self-parasitized hosts significantly more often than hosts parasitized by conspecifics when each host type is presented alone. Females faced with two previously parasitized hosts are not affected in their choice by the mating status (i.e. virgin or mated) of the previous parasitizing females. The combined results suggest that females are limited in their ability to assess the risk that their offspring will be attacked by a soldier, or that this risk is balanced by the relative advantages of ovipositing in a host parasitized by conspecifics. A possible advantage may be increased out-breeding opportunities for the emerging offspring. © 2009 The Authors. Journal compilation © 2009 The Royal Entomological Society.