Sex-allocation is an important issue in the conflicts of interests between males and females in social Hymenoptera. The sex-ratio of the conoly, which is determined by mating frequency of queens and other post-copulatory mechanisms, is not always optimal for both partners at the same time. This research aims to investigate the manipulative strategies developed by both partners to increase their degree of control on sex-ratio in several species of Formicidae. We will study the functional morphology of the genitalia and the mechanism of spermtransfer in different species, in relation to mating frequencies and effective paternities in colonies.