Studies on Culicoides species of Nigeria. VII. The biology of some Nigerian Culicoides species.

During field investigations into the biology of Culicoides species of Nigeria, 8,795 newly emerged Culicoides comprising of 20 species were caught with emergence traps at the Teaching and Research Farm of the University of Ibadan. Culicoides imicola Kieffer was the most predominant followed by C. quinquelineatus Goetghebuer and C. endelini Endeline. Two groups of Culicoides species were recognized. These were those breeding only during the rains with emergence peaks in June and August and those breeding throughout the year with low emergence during the dry season. Rainfall, temperature, relative humidity, the soil pH and its organic and mineral contents were found to influence Culicoides breeding. Low or traces of rainfall extended over 1-2 h were observed to be more favourable for Culicoides development than heavy rainfall which ended quickly within 1/2 h. A greater proportion of the Culicoides emerged during the night. It was concluded that the optimum temperature range for Culicoides emergence was 23-27 degrees C and optimum range of relative humidity 80-90%. Larvae were abundant on the soil throughout the year with a peak during the dry season; the seasonal abundance of pupae was similar to that of newly emerged adults. Although the fat-bodies of all the dissected newly emerged Culicoides were large, full and conspicious, those of about half of the Culicoides dissected in February and March contained larger, fuller and more conspicuous fat-bodies. It is suggested that the presence of such accumulated fatbodies during the onset of the rains immediately after the hot dry season signifies hibernation in these species.