The Probable Purpose of the Mid-coxal Prong in Brachycera (Diptera)

摘要

The mid-coxal prong is a narrow outgrowth from the distal sclerite of the coxa into the space between the coxa and the trochanter. It is present in members of most of families of flies (Brachycera). Its anterior face is hairy in large flies. The prong is the same in males and females and lacks any sensilla. It performs, presumably, some mechanical function. During flight the prong is clumped between the coxa and the trochanter, its anterior hairy face against a hairy field on the anterior coxal sclerite. The leg is put into its peculiar flight position by rotation of the trochanter. The trochanter presses the two hairy faces together. Morphology and biomechanics of the middle coxa suggest that the prong acts as a sort of a Velcro fastener, locking the middle leg in its flight position. However, excision of the prong impairs neither walking nor the ability to put the middle leg into a proper flight position and hold it against the strong head airstream.