Abstract
A survey of the species composition and distribution of the Culicoides midge populations at a range of sites where bluetongue is enzootic isolated a group of dominant species: C. cornutus, C. grahamii, C. magnus, C. milnei, C. pallidipennis and C. 23. dagger Monthly light-trap sampling of Culicoides showed that the population densities of the dominant species greatly increased after the rain seasons and that these species concentrated around flocks of sheep and cattle. The larval habitats of C. cornutus and C. pallidipennis were found associated with stock pens. Precipitin tests on blood-fed Culicoides showed that most of the dominant species regularly feed on sheep and cattle. Bluetongue virus was isolated from C. milnei, C. pallidipennis and C. 23. Serological surveys of wild and domestic bovids from the enzootic area showed a high proportion with antibody to bluetongue virus. The colonization of C. cornutus, a potential vector, is described briefly. A causal relationship between peak rainfall in April-May, peak numbers of Culicoides in May-June and peak bluetongue incidence in June-July is postulated. The vector status of the above species and C. austeni was evaluated.