The role of the antennae during courtship behaviour in the parasitic wasps Trichopria drosophilae

We have studied the courtship behaviour of Trichopria drosophilae Perkins (Hymenoptera: Diapriidae), a pupal parasitoid of the common fruit fly Drosophila melanogaster Meigen (Diptera: Drosophilidae), to understand the role of the antennae. Virgin pairs of the parasitoid perform an intense and stereotyped antennal courtship, which leads to copulation. During antennation, the two male fourth antennomeres come into contact with the two apical female antennomeres, and thus the secretion produced by the sex pheromone gland is spread onto the female receptors. By preventing the transfer of the courtship pheromone from male to female antennae, mating was inhibited. Moreover, selective ablation of single antennae demonstrated that the courtship pheromone acts on contact. When antennae of both sexes were partially removed (ablation at the same side, i.e. right or left) courtship was successful and copulation occurred. In contrast, in the case of antennal ablation at opposite sides, courtship failed despite the short distance between secretion and receptors. These results confirm the hypothesis that T. drosophilae male antennal glands are the release site of a contact courtship pheromone, playing a key role in mating behaviour. The occurrence of male antennal glands in Hymenoptera and other insect orders is discussed.