Cytotaxonomy of the Simulium damnosum complex and description of new cytotypes in the Tukuyu focus, southwest Tanzania.

Larvae of Simulium damnosum complex collected from rivers draining Tukuyu onchocerciasis focus were chromosomally examined. Of the 970 larvae analysed, 910 were identified as Kiwira form, a newly described cytotype found in all S. damnosum larval habitats in the Tukuyu area, while 51 were classified as a new subpopulation, tentatively named as Kasyabone form. The F1 larval progeny obtained from wild caught human biting S. damnosum and reared in the laboratory were chromosomally examined. 509 F1 larvae from 70 females blood fed on human volunteers were identified as Kiwira form. As the main human-biting member of the complex in the Tukuyu area, and because some of the wild caught females had developing filarial larvae indistinguishable from those of Onchocerca volvulus, Kiwira form is thus incriminated as the local vector of onchocerciasis. These observations are discussed with respect to previous literature.