Males do not like the working class: male sexual preference and recognition of functional castes in a primitively eusocial wasp

Discrimination among potential partners is a critical step in sexual selection to avoid wasting reproductive resources on an unsuitable mate. In the female-dominated hymenopteran societies males have often been regarded as 'flying sperm containers' spending all their time and energy in trying to acquire a mate. We investigated the male sexual preference for potential partners using as a model the primitively eusocial wasp Polistes dominula in which female caste is rather flexible and difficult to determine. By means of laboratory bioassays, we compared the males' behaviour towards females of different reproductive potential. Males were able to recognize female castes, strongly preferring reproductive females to workers, regardless of female age or health. The results show that in this species caste plays a key role in orienting male discrimination and preference, presumably through chemical cues, towards reproductive females both healthy and parasite-castrated. Overall, our study shows that social Hymenoptera males are not always 'small mating machines' eager to mate.