Sexual behavior and morphology of Themira minor (Diptera: Sepsidae) males and the evolution of male sternal lobes and genitalic surstyli

Probable ancestral types of courtship behavior for most sepsid flies were deduced from the behavior and morphology of a species in the relatively basal genus Themira . At least three of the five behavior patterns used by Themira minor (Haliday) males to court females prior to and during copulation are shared with other, more derived groups. During copulation the male's sternal lobes were rotated so that their brushes of long setae were fanned apart and may tap the female. The morphology of the tips of the male's genitalic surstyli and the muscles attached to them indicate that they are also moveable. This trait, which occurs in several other distantly related species, probably serves to squeeze the female during copulation. Thus, contrary to the impression from previous studies, elaborate courtship before and during copulation may be widespread among sepsids.