From March to October 1984, targets consisting of black cloth and netting, baited with l-octen-3-ol (released at about 0-5 mg/h), and acetone (about 100 mg/h) or butanone (15 mg/h), and coated with deltamethrin, were deployed at 3-5/km 2 in 600 km 2 of the Zambezi Valley of Zimbabwe where Glossina morsitans morsitans Westwood and G. pallidipes Austen were initially abundant. About 3 000000 adults of G. pallidipes and 200000 of G. m. morsitans originally present in the area as adults or pupae were killed by targets or removed by sampling procedures between March and December. At the end of this period, the tsetse populations in the centre of the block had declined by at least 99-99%. The targets dealt adequately with a strong invasion pressure from initially dense infestations nearby, partly because the targets reduced the abundance of tsetse up to 5-10 km outside the block. At 18 months after the start of the study, the targets were badly faded; this was corrected by spraying them with a black dye and an ultraviolet-light absorber that protected the dye and insecticide, but by then the targets had deteriorated and were without adequate odour attractant, and many were no longer being maintained. Tsetse then invaded further into the block, but only in small numbers. Tabanids and muscoids were not strongly attracted to targets; their population densities in and near the block did not change greatly. Targets offer a simple and ecologically clean method of controlling tsetse and preventing invasion.

Bioassays in Zimbabwe with wild-caught Glossina pallidipes Austen and G. morsitans morsitans Westwood showed that formulations of deltamethrin (Decatix, SpotOn and an experimental variant of SpotOn), alphacypermethrin (Renegade) and cyfluthrin (Cylence) applied to oxen at the manufacturers' recommended doses gave knockdowns above 50% for 5-24 days in hot months and 24-55 days 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 belly. At other times the front legs were preferred, especially in the wet season and for a few months after. Chemical assays indicated that insecticide persisted at greatest concentration on the backs of oxen and least on the legs. Modelling the experimental data suggested that 4-21 annual applications of insecticide in areas >1000 km 2 would give good control at least 10 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. Dead beetles occurred in and near fresh dung.Bioassays and behavioural studies were performed at Rekomitjie Research Station in the Zambezi Valley of Zimbabwe where Glossina pallidipes Austen and G. morsitans morsitans Westwood occur. Test cattle were brown or black oxen with a high proportion of indigenous blood, and weighed an average of 420 kg (range 345-561). Toxicity and persistenceEach of the test oxen was treated separately with one of the following proprietary insecticides, at doses recommended by the manufacturers.

An operation is described in which approximately 100 sq. miles of heavily infested tsetse country in Southern Rhodesia, supporting both Glossina morsitans Westw. and G. pallidipes Aust. and an abundant and varied game population and formerly an area of endemic sleeping sickness attributable to Trypanosoma rhodesicnse, received six applications of 4 per cent, γ BHC in diesolene, discharged from aircraft in the form of a coarse aerosol, between May and September 1957. The area was a valley bounded by an escarpment, which provided conditions of relative isolation.Fly-round catches of G. morsitans taken before, during and after the operation indicated that in those parts of the area that had received uniform treatment an estimated reduction in population, after the final application, of between 96·6 and 100 per cent, had been achieved, but where only the vegetation forming the riverine fringes had been treated the reduction was less. Quantitative data on the effect of the treatment on G. pallidipes were not collected, but the species ceased to be found in an investigation on sampling techniques that had been in progress in the area.The area had been chosen for a resettlement scheme of indigenous people that was due to begin before October 1957, and the purpose of the spraying operation was to reduce the population of tsetses to a level that would permit the introduction of the people and their stock with comparative safety from trypanosomiasis. It was hoped that the number of people to be resettled would be sufficient to clear most of the tsetse habitat in their text-abstract agricultural activities and that the tsetses would be permanently excluded from the valley. Four to five years after the start of resettlement there were still several uncleared areas remaining, but the situation was continually improving, and estimates in 1962 indicated that the population of G. morsitans had remained at a low level, showing a reduction of between 81 and 100 per cent, as compared with that prevailing before the spraying operation. The stock introduced in 1957 were maintained under drug treatment, and the rate of infection with T. congolense was kept below a 3 per cent, level; no cattle died from trypanosomiasis, and their numbers had more than doubled by 1962. No case of sleeping sickness occurred.The work described here showed that, under conditions of relative isolation, G. morsitans can be sufficiently reduced in numbers by means of an insecticidal aerosol discharged from aircraft to permit the successful introduction of people and stock, provided that adequate veterinary supervision is given, and that under these conditions settlement can prevent the recovery of a population of this species.

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