Males of the social wasp Ropalidia marginata can feed larvae, given an opportunity

A striking feature of hymenopteran societies is the general absence of male workers. There are some reports of males feeding larvae in some social wasps, but not in the extensively studied Ropalidia marginata. By providing excess food and by removing the females, we investigated whether males are incapable of feeding larvae or lack opportunities to do so. Males fed larvae with probabilities and rates comparable to those of females, suggesting that lack of preadaptation to feed larvae does not explain the absence of male workers in social Hymenoptera. Although males were not as efficient as females at feeding larvae, they seemed capable of doing enough for natural selection to have promoted the evolution of male workers if there were not other factors preventing it. Genetic relatedness asymmetry may be one such factor. A third hypothesis for the absence of male workers in social Hymenoptera, concerning the increased susceptibility of haploid males to infection, is not relevant because males handle and masticate prey for their own consumption and otherwise interact with the larvae.