Host discrimination and egg laying in Anisopteromalus calandrae (Hymenoptera: Pteromalidae) ectoparasitoid of Callosobruchus maculatus (Coleoptera: Chrysomelidae)

• Females can discriminate between unparasitized hosts and hosts parasitized by themselves or by conspecific females.
• Superparasitism rate depend on the identity of the first female and on the interval between successive egg laying.
• Host discrimination is mediated by external semiochemical markers, but the nature of the markers was not determined.
• The decrease in superparasitism avoidance could be linked to the decay of the marker.

The recognition and avoidance of already parasitized hosts is a major issue in parasitoid behavioral ecology, particularly for solitary species. Superparasitism avoidance is often described as an adaptive strategy, and the discrimination abilities of parasitized hosts have been selected in many species. The recognition of parasitized hosts often relies on olfactory cues or a marking pheromone that could decay with the time between successive host encounters. The intraspecific discrimination abilities of the solitary parasitoid Anisopteromalus calandrae (Hymenoptera: Pteromalidae) have been studied in the laboratory under several conditions. While the discrimination abilities of recently parasitized hosts and those parasitized for a longer time (i.e. when the first egg is about to hatch) are known in this species, their capacity to discriminate hosts containing eggs at intermediate stages and their capacity to adapt superparasitism avoidance depending on the identity of the first female has not been explored. The present study investigated (i) females' behavior in the presence of hosts parasitized by themselves or conspecifics with varying time intervals, and (ii) whether these females were able to adapt their reproductive strategy when placed in a choice and a no-choice situation.Our experiments confirmed that A. calandrae females are able to discriminate between parasitized and unparasitized hosts, as they laid more eggs on the latter. However, they did not recognize hosts containing eggs of a conspecific at intermediate developmental stages, when placed in either a choice or a no-choice situation. The same phenomenon was observed in a self-superparasitism situation in a choice experiment. By contrast, in a no-choice situation, they recognized hosts containing eggs that had been freshly laid by themselves, but not those at an intermediate stage of development.