How important is sex for females of a haplodiploid species under local mate competition?

Abstract

Virgin females of Hymenoptera are still able to reproduce by laying unfertilized eggs that develop into male offspring (arrhenotokous haplodiploidy). Therefore, these constrained females may face a conflict between searching hosts and obtaining immediate fitness or investing time and energy in finding a mate enabling them to produce offspring of either sex. We studied this conflict in Nasonia vitripennis Walker (Pteromalidae), a pupal parasitoid of numerous fly species, by investigating olfactory preferences of constrained females for the male sex pheromone and host odor, respectively. According to Godfray’s constrained model, females of haplodiploid species gain only little advantage from mating when population sex ratio is at equilibrium. However, in species with local mate competition like N. vitripennis, females are predicted to invest comparatively more time and energy in mating activities. In behavioral 2-choice experiments, virgin females were innately attracted to both male pheromone deposits and the odor of host puparia. When given the choice between these 2 stimuli, virgin females preferred the pheromone even when they were allowed to associate host odor with oviposition success prior to the bioassay. Immediately after mating, however, the olfactory preference of females switched to host odor. We conclude that constrained females of N. vitripennis are much more motivated to invest in mate finding than in host finding as predicted by the constrained model. The results are discussed with respect to the ecology of N. vitripennis. Key words: constrained model, host odor, male sex pheromone, mate finding, Nasonia vitripennis, parasitic wasp. [Behav Ecol]