Molecular Identification of Onchocerciasis Vector Sibling Species in Black Flies (Diptera: Simuliidae)

A number of sibling species in the Simulium damnosum species complex transmit River Blindness (onchocerciasis) in tropical Africa. Black fly sibling species can be reliably recognized only through analysis of the larval polytene chromosomes. The routine, unambiguous assignment of the potentially disease-transmitting adult females to a particular species is virtually impossible. Two molecular assays to identify the sibling species of biting female flies are presented. The first relies on PCR-mediated amplification of internal transcribed spacers of the nuclear rDNA loci while the second involves immunoblotting of silk proteins which are expressed in both larvae and adult females. Both assays yield sibling-specific size markers that can be used to identify the sibling species of biting adult females. To illustrate the use of these assays, a molecular characterization is given for two S. damnosum siblings (squamosum, sirbanum) collected from cytologically verified populations, and a partial characterization of a third sibling (damnosum s. str.) found as a contaminant in these samples.