, 802–806 © 2004 British Ecological Society

Host acceptance decision in parasitic wasps depends strongly on the parasitism status of the encountered host. In solitary species, a host allows the development of only a single parasitic larva, and then any oviposition in an already parasitized host leads to larval competition and to potential loss of offspring. The ability of parasitoids to discriminate between parasitized and healthy hosts is well documented. Despite this, parasitized hosts are still accepted by the foraging wasps, an occurrence termed superparasitism. 2. In the last decades, theoretical studies have suggested that under certain circum-stances superparasitism can be optimal. Generally, the superparasitism theory predicts that the optimal host acceptance decision should follow a zero-one rule: in response to both environmental and physiological state characteristics, a given female should switch from acceptance to rejection of parasitized hosts