Boletín de la AeE

O. basalis is a solitary ectoparasitoid which has larvae that develop at the expense of the larvae or pupae of bruchids. The females have to perfórate the seed tegument to access hosts which spend all their developmental period within a seed. Laying several eggs on the same host (i.e. superparasitism) causes larval competition. Studies which have been performed on solitary species have shown that the female strategy in this situation strongly depends on the ability to discriminate the age of the first parasitoid. This population of D. basalis develops inside stores where females frequently encounter parasitised hosts and conspecifics. The aim of this study was first to analyse the ability of females to discriminate the age of the first parasitoid and the consequences of such behaviour, and second to investígate whether the conspecific presence influence the reproductive behaviour of the females.

The analysis of behavioural sequences and the reproductive activity of females in different situations shows that they discriminate between parasitised and unparasitised potential hosts and that they can evalúate with precisión the time elapsed since a previous egg was laid. But females do not always avoid parasitised hosts. When a host bears an egg, female response depends on the origin of the first egg (self or conspecific superparasitism) and the time elapsed since the first egg was laid. The observation of larval fighting shows that there is a positive relationship between host acceptance and survival probability of the second egg laid. Furthermore, when there are 24 h oíd parasitoid eggs or larvae in a host-patch, the fecundity of females decrease (from 6.22 to 1.81 eggs/day). After several days we observe the features of oosorption in ovocytes.

A female can perceive the presence of a parasitoid on a host, but the overall strategy of egg-laying depends on the time elapsed since a previous egg was laid and also on the presence of conspecifics foraging on the patch, as predicted by the optimal foraging model.

We have shown that host discrimination occurs when a female inspects a host with its ovipositor. Females perceive information emanating from developing embryos. After eclosión, information is derived from parasitoid larvae and probably from the now parasitised host larvae. Behavioural studies and observations by scanning electrón microscopy show that this information is perceived by gustatory receptors on the ovipositor.