Histological Structure of the Clypeo-Cibarial and LabralSkeleton and the Musculature in the Lower Asilomorpha(Diptera): 1. Rhagionidae and Tabanidae

摘要

Females and males of rhagionids, and also tabanid females have a strongly sclerotized clypeus firmly merged with the frons and genae. Their proboscis is unfolded and almost immovable in the sagittal plane. The clypeus of Chrysops relictus males consists of thick but non-sclerotized cuticle. In all the species investigated, the clypeal ridges are weakly developed and merged with lateral cibarial ribs over a small area of the distalmost edge of the cibarium. The two pairs of cibarial muscles, ending onthe dorsal cibarial cornua, apparently act as antagonists and stabilize the position of the proximal end of the cibarium. The rhagionid labrum is well developed and its outer and inner epipharynx walls are sclerotized. In blood-sucking tabanid females, the labrum is sclerotized to a great extent, and the epipharynx has longitudinal ridges protruding into the labral cavity. The same structure of the labrum is found in non-blood-sucking females of Symphoromyia crassicornis, suggesting a recent loss ofblood-feeding in this species. The labrum of tabanid males has a weakly sclerotized epipharynx without longitudinal ridges and an almost non-sclerotized outer wall. On the whole, all the species studied are characterized by three main features: unfoldedproboscis, immovable clypeus tightly merged with the frons and genae, and a completely developed pharynx.