Cytotaxonomic confirmation of two forms of Simulium sirbanum in the eastern part of the Onchocerciasis Control Programme in West Africa

An earlier report (Cheke et al., 1987) of morphological differences between populations of Simulium sirbanum Vajime & Dunbar in West Africa was confirmed cytotaxonomically. Populations with adult males having Type III scutal patterns were associated with male larvae heterozygous for the inversion IS-3, whereas adult males with Type IV scutal patterns were associated with larvae homozygous for IS-3. The taxonomic implications are briefly discussed but the evidence is considered to be inappropriate for resurrecting S. sudanense Vajime & Dunbar. Aspects of the biology of the two forms and their importance in onchocerciasis transmission are discussed.