Microsculpture and phylogenetic significance of the spermatheca of black flies (Diptera : Simuliidae)

The highly varied spermatheca of black flies provided an under-studied char acter system for phylogenetic reconstruction of the Simuliidae. Scanning el ectron microscopy of the spermatheca of 17 simuliid species elucidated fold s and spicules on the inner surface; callosities, anastomosing ridges, and minute tubercles on the outer surface; and an intricately fluted spermathec al duct. The spermatheca of Parasimulium crosskeyi, the most plesiomorphic taxon, had a slightly wrinkled inner surface and an outer surface with acut ely raised polygonal ridges. Species hypothesized to be among the basal lin eages of the simuliids (e.g., Helodon susanae and Prosimulium magnum) had a n irregularly folded inner spermathecal surface, but their relationships we re not well resolved on the basis of information about the spermatheca. Mor e evolutionarily derived species, including a number of species in the genu s Simulium, had short or filiform spicules on the inner surface of the sper matheca. Although the use of a single character system, the spermatheca, di d not fully resolve relationships among Simuliidae, its utility as a rich s ource of phylogenetic information was demonstrated.