Behavioural and physiological responses to conflicting oviposition stimuliin a synovigenic parasitoid

The behavioural and physiological responses of the synovigenic parasitoid, Dinarmus basalis (Rond.) (Hymenoptera: Pteromalidae), were investigated whi lst the wasps were submitted to conflicting oviposition stimuli: an environ ment which induced them to restrict egg-laying and a physiological factor, egg-load pressure, which induced them to lay eggs. When individual females depleted patches containing hosts parasitized 24 h or 72 h beforehand, they laid preferentially on unparasitized hosts and the number of eggs laid dec reased significantly. Although they remained for several days in such patch es, egg-load pressure did not lead them to modify their strategy (i.e. to a ccept all the available hosts including the already parasitized ones). In t his synovigenic species, the oviposition constraint resulted in the retenti on of oocytes. Dissection and histological observation showed that the unla id eggs are resorbed, a reproductive regulatory process which has seldom pr eviously been reported in the presence of unparasitized hosts. This physiol ogical response was induced by the mere presence of the parasitized hosts r ather than their density. The females' response was also influenced by the presence of conspecifics. They still avoided laying on parasitized hosts bu t the number of eggs laid daily became comparable to that observed in patch es containing only unparasitized hosts. Thus, D. basalis females adapted th eir strategy in response to their environment, in which the most significan t factor seemed to be the quality of the hosts provided, and their physiolo gy. The originality and the importance of these results are discussed.