SIBLING SPECIES DISTRIBUTIONS OF THE SIMULIUM-DAMNOSUM COMPLEX IN THEWEST-AFRICAN ONCHOCERCIASIS CONTROL PROGRAM AREA DURING THE DECADE 1984-93, FOLLOWING INTENSIVE LARVICIDING SINCE 1974

During the decade from 1984 to 1993, nine species of the Simulium damn osum complex of blackflies (Diptera: Simuliidae) were identified from the area covered by the Onchocerciasis Control Programme. These were S . damnosum s.s., S, dieguerense, S. konkourense, S. leonense, S. sanct ipauli, S, sirbanum, S. soubrense, S. squamosum, and S. yahense. Some of these species were found to consist of two chromosomal variant popu lations. These were S. konkourense 'Konkoure' and 'Menankaya' forms, S . sanctipauli sensu stricto and 'Djodji' form, S. soubrense 'Chute Mil o' and 'Beffa' forms. The distribution of these twelve cytological tax a was assessed in relation to the two main vegetation zones of West Af rica (forest and savanna), topography, river size and other factors. T he range of each species was influenced by seasonal climatic changes i n wind movement and river water level. The most widely distributed spe cies were S. sirbanum and S. damnosum s.s., associated with savanna ar eas, recorded from all river basins. Simulium dieguerense was restrict ed mainly to Western Mall on the Rivers Bafing and Bakoye in the Seneg al River basin. Simulium squamosum was identified from rivers draining mountainous areas in both the forest and savanna zones. Simulium yahe nse was found in small permanent rivers along a wide forested band par allel to the coast and was absent from the plains of Togo and Benin. M embers of the S. sanctipauli subcomplex had restricted distributions e xcept for S. sanctipauli s.s., which was widespread in large rivers of the forest zone from Sierra Leone to the Volta Lake in Ghana. Simuliu m soubrense 'Beffa' form occurred in Togo and Benin, S. soubrense 'Chu tes Milo' form in Guinea, both 'Konkoure' and 'Menankaya' forms of S. konkourense occurred predominantly in Guinea and S. leonense in Sierra Leone. The relevance of the distribution maps and the importance of t he data bank to vector control larvicidal operations are discussed.