Use of morphological characters in the study of Simulium damnosum s.l. populations in West Africa.

Morphological characters were tested which could be used to compare and to associate Stimulium damnosum s.l. populations reinvading the area of the Onchocerciasis Control Programme in the Volta River basin with those of potential source areas. The savanna cytospecies S. damnosum s.str. and S. sirbanum could be distinguished from the forest species S. sanctipauli, S. soubrense and S. yahense by the size and shape of the antennae and the colour of the basal wing tufts. Wing tufts of S. squamosum were of variable colour. Results did not confirm morphological keys for the complex which used counts of maxiillary teeth to separate S. damnosum s.str. and S. sirbanum, and numbers of spinules on the radial vein of the wings to separate S. yahense and S. squamosum. Populations of the S. damnosum complex could be characterised by morphometric methods. Measurements of the length of the thorax provided a rapid and easy means to distinguish different populations. The length of the thorax was positively correlated with the length of the wings. By using several measurements in combination populations could be more clearly characterised.