The evolution and maintenance of sexual reproduction is believed to involve important tradeoffs. The queens of social insects are faced with a dilemma over the costs and benefits of sexual and asexual reproduction. Asexual reproduction by a queen doubles her contribution to the gene pool. However, overuse of asexual reproduction reduces the genetic diversity of the offspring and thus the ability of the colony to adapt to environmental stress. Recent research suggests that queens of some termite species can solve this tradeoff by the conditional use of sexual and asexual reproduction, whereby queens produce the next generation of queens by parthenogenesis but use sexual reproduction to produce other colony members. This reproductive system, so called AQS (Asexual Queen Succession), has been found in Reticulitermes speratus, R. virginicus R. lucifugus and in some higher termites, indicating that it has evolved multiple times independently in termites. In the AQS species, queens produce parthenogenetic offspring under the presence of kings by closing micropyles (sperm-gates, i.e., tiny openings for sperm entry) of their eggs. I discuss possible physiological mechanism and genetic background underlying the asexual queen succession system in the AQS species. In addition, AQS system and consequent sex-asymmetric inbreeding provide ideal opportunity to test kin selection in diploid organisms, although a strong test of the theory has proven difficult in diploid social insects because they lack relatedness asymmetry unlike Hymenoptera.