Insecticide-treated cattle for controlling tsetse flies (Diptera : Glossinidae): some questions answered, many posed

Bioassays in Zimbabwe with wild-caught Glossina pallidipes Austen and G. mo rsitans morsitans Westwood showed that formulations of deltamethrin (Decati x, SpotOn and an experimental variant of SpotOn), alphacypermethrin (Renega de) and cyfluthrin (Cylence) applied to oxen at the manufacturers' recommen ded doses gave knockdowns above 50% for 5-24 days in hot months and 24-55 d ays at cooler seasons. Within these periods, the average knockdowns were 77 -86% with deltamethrin, 74% with alphacypermethrin and 59% with cyfluthrin. None of the insecticides affected the numbers of tsetse attracted to oxen from a distance, the proportion of tsetse that engorged, and the alighting responses on cloth screens. In the hot season most tsetse engorged on the b elly. At other times the front legs were preferred, especially in the wet s eason and for a few months after. Chemical assays indicated that insecticid e persisted at greatest concentration on the backs of oxen and least on the legs. Modelling the experimental data suggested that 4-21 annual applicati ons of insecticide in areas > 1000 km(2) would give good control at least 1 0 km from the invasion source if the treated cattle contributed at least 50 % of tsetse diet. No treatment regime under any diet conditions would give good control near an invasion front. Insecticide at concentrations up to 0. 15 ppm occurred in dung from treated oxen for up 12 days post-treatment. De ad beetles occurred in and near fresh dung.