The interaction between sex and altruism has been a central issue in evolutionary biology, since W. D. Hamilton has explained the evolution of sterile workers in hymenopteran insects by haplodiploidy that involves parthenogenesis producing males (arrhenotoky) in the life cycles. Recently, the other type of parthenogenesis, thelytoky (the female producing one), is also a central focus. By thelytoky females can produce genetically highly related direct offspring. In social hymenoptera the body of recent findings indicates that thelytoky is often associated with cheating or intraspecific social parasitism. This is theoretically reasonable, because thelytoky can extend options of hymenopteran workers which otherwise can produce only drones. Furthermore, such a selfish option gives rise to new conflict with other parties such as males, leading to the evolution of various counter strategies. In this talk I overview thelytoky in social insects and discuss that at least three different consequences of thelytoky can result. 1. The collapse of the colony or the extinction of the population. 2. The fixation of an asexual genotype, which does not result in the population extinction but leading to the resolution of conflict at least in the short term owing to the clonal nature of colonies. 3. The maintenance of eusociality and sex by the power balance of counter strategies.