Abundance and Temporal and Spatial Distribution of Culicoides Brevitarsis Kieffer (Diptera: Ceratopogonidae) on Cattle in South-East Queensland.

Abstract

Numbers of C. brevitarsis on cattle in south-east Queensland increased rapidly from zero at 0.5 h before sunset, to a peak during the half hour after sunset, then decreased to zero in the following 5-6 h and remained at zero throughout the day. On standing animals abundance was greatest on the ridgeline at the tail, decreasing rapidly down the flank and less rapidly towards the head. On mature animals abundance after sunset halved with each increase of 0.53 m s-1 in wind speed, each increase of 6.4ºC, each decrease of 158 Pa vapour pressure deficit, and each additional 38 min after sunset. Only females were collected from cattle; 97% of nullipars were mated. They did not always feed at their first attempt and were much less likely to feed on some hosts than others. Close shaving did not alter the number of flies on small areas and did not prevent feeding. Before sunset C. brevitarsis were observed more frequently on hosts in the absence of direct sunlight. In direct sunlight, abundance was influenced most by wind speed (positive), minutes before sunset (negative) and temperature (negative), in order of decreasing importance. Without direct sunlight, the factors were minutes before sunset (negative), temperature (positive), and wind speed (negative); after sunset the factors were wind speed (negative), vapour pressure deficit (positive), minutes after sunset (negative) and minor effects from time of year and temperature.