In 54 light-trap collections made at 28 sites in the Onderstepoort area a total of 178 941 Culicoides midges
of 35 species was collected in March 1988; the survey was repeated at 26 sites in September and yielded
19 518 Culicoides of 24 species. The number of Culicoides species collected totalled 38. C. imicola was
the most abundant species at 27 of the 28 sites sampled, and accounted for 88% and 67% of all midges
collected in the two months respectively. This study not only confirms that C. imicola is widespread and
abundant in the greater Onderstepoort area, but also that its numbers correlate positively with the historical
prevalence of African horse sickness (AHS) and bluetongue (BT) locally.
The high numbers of C. imicola make Onderstepoort the ideal site for the study of its laboratory vector
capacity. The relatively low numbers of Culicoides spp. other than C. imicola in the Onderstepoort area,
will severely limit studies on their roles in the transmission of arboviruses.
The origin of the blood-meals of 1 338 engorged Culicoides belonging to 13 species was determined by
means of a cross-over electrophoresis precipitin test; C. imicola fed on cattle, horses, sheep and pigs.
Four other Culicoides species showed a similarly wide host range.