A Remarkable Species of Drosophilid Fly (Diptera) with “Mandibles”

A distinctive species in the family Drosophilidae, Drosophila ancora Okada, 1968, is redescribed from specimens from Vietnam, and transferred to the genus Dichaetophora Duda sensu lato. It is exceptional among Diptera for its labellar sclerites that in males have grown into a pair of heavily sclerotized, pointed lobes at the tip of the labellum, producing what appear to be chewing mandibles. This is analogous to the condition in the dolichopodid Melanderia Aldrich, but there it is not sexually dimorphic. The structures are doubtfully used in male-male aggression or in postcopulatory mate guarding. Based on their shapes and fit, it is proposed that the “mandibles” are used by males to grasp the tip of the female oviscapt during courtship or for the male to grasp the female wing edge while mounted.