SUPERPARASITISM AND HOST DISCRIMINATION IN THE SOLITARY ECTOPARASITOID DINARMUS-BASALIS

In the solitary ectoparasitoid, Dinarmus basalis (Hymenoptera: Pteroma lidae), the occurrence of superparasitism according to the unparasitis ed host density, and the nature of the host(s) provided was investigat ed in laboratory studies. In this species superparasitism was observed whatever the experimental conditions used, but the degree of superpar asitism depended on the density of its host, Bruchidius atrolineatus ( Coleoptera: Bruchidae). Superparasitism was due to successive egg-layi ng phases on the same host. However, females were able to discriminate between unparasitised hosts and hosts parasitised from 8 h to 72 h be forehand by themselves or by conspecifics. There was no conclusive evi dence that superparasitism in the presence of a host parasitised 30 mi n before was linked to an absence of host discrimination. Host discrim ination in this species is achieved by host-quality markers. These are individual-specific markers since conspecific superparasitism rates w ere often higher than self superparasitism rates. One deterrent substa nce is emitted by the females during oviposition onto the egg or relea sed by the 16 to 24 h-old egg itself. Another host-quality marker is a ssociated with the presence of a larva on its host. On the other hand, host discrimination ability did not always imply avoidance of superpa rasitism. In D. basalis there exists a positive relationship between t he survival probability of the second egg and the tendency to superpar asitise, and superparasitism could therefore result in a significant f itness gain. Under our experimental conditions, D. basalis females exh ibited a wide range of oviposition behavioural plasticity in relation to the parasitoid developmental stage, the type of superparasitism, an d the encounter rate with unparasitised hosts.