The roles of foraging environment, host species, and host diet for a generalist pupal parasitoid

Abstract

Even for parasitoids with a wide host range, not all host species are equally suitable, and host qualityoften depends on the plant the host feeds on. We compared oviposition choice and offspring perfor-mance of a generalist pupal parasitoid,Pteromalus apum(Retzius) (Hymenoptera: Pteromalidae), ontwo congeneric hosts reared on two plant species under field and laboratory conditions. The plantscontain defensive iridoid glycosides that are sequestered by the hosts. Sequestration at the pupal stagediffered little between host species and, although the concentrations of iridoid glycosides in the twoplant species differ, there was no effect of diet on the sequestration by host pupae. The rate of success-ful parasitism differed between host species, depending on the conditions they were presented in. Inthe field, where plant-associated cues are present, the parasitoid usedMelitaea cinxia(L.) overMeli-taea athalia(Rottemburg) (Lepidoptera: Nymphalidae), whereas moreM. athaliawere parasitisedin simplified laboratory conditions. In the field, brood size, which is partially determined by rate ofsuperparasitism, depended on both host and plant species. There was little variation in other aspectsof offspring performance related to host or plant species, indicating that the two host plants are ofequal quality for the hosts, and the hosts are of equal quality for the parasitoids. Corresponding tothis, we found no evidence for associative learning by the parasitoid based on their natal host, so withrespect to these host species they are truly generalist in their foraging behaviour.