Evaluation of insecticide‐treated cattle as a barrier to re‐invasion of tsetse to cleared areas in northeastern Zimbabwe

Abstract

A field trial in Zimbabwe investigated the efficacy of insecticide-treated cattle as a barrier to prevent the re-invasion of tsetse, Glossina morsitans and G. pallidipes (Diptera: Glossinidae), into cleared areas. The original tsetse barrier consisted of insecticide-treated odour-baited targets, at an operational density of four to five targets per km2, supported by insecticide-treatments of cattle with either deltamethrin dip (Decatix, Coopers) at two-weekly intervals, or deltamethrin pouron (Spoton, Coopers) at monthly intervals, in a band approximately 20 km wide from the re-invasion front. Tsetse catch, and trypanosomiasis incidence in nine sentinel herds was recorded for 7-8 months, respectively, before the targets were removed, leaving only the insecticide treatment of the local cattle to stem the re-invasion of tsetse. After the removal of the target barrier, the tsetse readily invaded the trial area and the incidence of trypanosomiasis in sentinel herds increased, while their PCVs decreased. After seven months without the targets in place, trypanosomiasis prevalence in the local stock had reached alarmingly high levels; the trial was terminated prematurely and the target barrier re-deployed. Immediately after the re-deployment of the target barrier, the tsetse catch in the trial area reverted to acceptable levels along the re-invasion front, and trypanosomiasis incidence in the sentinel cattle decreased. It is concluded that, under the conditions of the field trial, the insecticidal treatment of local cattle did not in itself form an effective barrier to tsetse re-invasion. By contrast, the target barrier performed as was predicted by mathematical and experimental analysis, and readily cleared the tsetse infestation and reduced trypanosomosis incidence in the trial area.

Is the Even Distribution of Insecticide-Treated Cattle Essential for Tsetse Control? Modelling the Impact of Baits in Heterogeneous Environments

“…The cost is $231, and the disease risk has been longer and more widespread. Present indications for the speed at which tsetse invade after reducing the restrictions, and the ease with which prompt action can restore the situation, accord with field experience [24].…”

Olfaction in vector-host interactions

“…However, while insecticide-treated cattle offer a particularly cheap and sustainable method of tsetse, we suggest that odour-baited targets and traps will continue to play an important role. First, cattle are not evenly distributed and thus to achieve success it is frequently necessary to deploy artificial baits in areas where cattle are absent or where other hosts are abundant , Warnes et al 1999. Second, while insecticide-treated cattle may be effective for controlling vectors of T. b. rhodesiense, this approach may be less applicable for vectors of T. b. gambiense, where cattle play a less important role in both disease epidemiology and tsetse diet.…”

Release-Recapture Studies Confirm Dispersal of Glossina palpalis gambiensis between River Basins in Mali

“…More recently, insecticide-impregnated cloth targets deployed at ∼250 m intervals forming a barrier with a width between 2 and 25 km successfully prevented reinvasion of G. m. centralis in the Okavango delta in Botswana [4]. These barriers can be reinforced using insecticide-treated cattle [17]. However, most of these barriers have been shown to have a very low temporal efficacy as they require proper maintenance, and in most cases, they have proven not to be sustainable [18].…”