A METHOD FOR THE ASSESSMENT OF BLACKFLY (DIPTERA, SIMULIIDAE) ATTRACTION TO AND ENGORGEMENT ON SHEEP IN SOUTH-AFRICA

A suspended-net technique was used to capture blackflies attracted to and engorging on Dorper and Merino sheep on irrigated pastures. Two ba it animals of each breed were restrained individually in wire-mesh enc losures located within four larger pens, each containing nine more ani mals of the same breed. Nets were suspended partly over the restrained animals and blackflies were collected at the end of 2-hour or longer periods. Mean numbers of blackflies captured in association with Merin o (73,3/h) and Dorper sheep (89,1/h) did not differ significantly. Num bers of captured blackflies correlated (rho = 0,8361) with levels of i rritation shown by sheep. Engorgement on Merinos was significantly (p = 0,009) higher than on Dorpers. Percentage engorgement was low, mostl y below 10% on Merinos and below 5% on Dorpers. When high wind speeds and high saturation deficits (associated with temperatures in the mid- thirties) occurred, the success of capture was impaired. The technique is useful for quantifying the abundance of irritating blackflies in t he immediate proximity of smallstock under experimental conditions.