Lack of discrimination of sex and maturity of conspecifics in the copulation attempts of the male stalk-eyed fly,Sphyracephala detrahens (Diptera: Diopsidae)

Among insects, males have evolved the ability to discriminate potential mates to avoid vain mating attempts. In Diptera, courtship and mating behaviors of species that do not discriminate potential mates have rarely been studied. In this study, we investigated copulation attempts of the stalk-eyed fly, Sphyracephala detrahens males, which do not engage in any observable pre-copulatory courtship behavior. We found that sexually mature males attempted to copulate with mature males and immature adults of both sexes, as frequently as with mature females. Successful copulation only occurred with mature females. Immature females rejected mounting males by vibrating their bodies and immature and mature males by incurving their abdomen downward. Comparison of the cuticular hydrocarbon components of individuals of different sexes and maturity levels indicated that the cuticular hydrocarbon profiles were similar regardless of the sex and sexual maturity. Therefore, we suggest that visual or chemical information are of little use for males S. detrahens in discriminating receptive conspecific mates. Since elaborate mate discrimination behaviors lead to additional time and energy costs when discrimination is difficult, S. detrahens may increase reproductive success simply by increasing the number of copulation attempts. Digital video images related to this article are available at http://www.momo-p.com/showdetail-e.php?movieid=momo211123sd01a, http://www.momo-p.com/showdetail-e.php?movieid=momo211123sd02a, http://www.momo-p.com/showdetail-e.php?movieid=momo211123sd03a, and http://www.momo-p.com/showdetail-e.php?movieid=momo211123sd04a.