The Experimental Application of Insecticides from a Helicopter for the Control of Riverine Populations ofGlossina tachinoidesin West Africa. VII. Studies on the Physical Properties of Sprays of Endosulfan and Deltamethrin applied toG. tachinoideshabitats in the R. Komoe Valley, Upper Volta

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Abstract
Physico-chemical studies of insecticide sprays applied by helicopter were undertaken during the course of the WHO Phase II aerial spraying trials for riverine Glossina [vector of human trypanosomiasis] control in Upper Volta during the 1977-1978 dry season. A Bell 47G-4A helicopter was fitted with electrically operated rotary atomizers and the equipment was calibrated to apply insecticides at very low dosages (endosulfan 100 g/ha and deltamethrin 12.5 g/ha). Distribution of insecticide deposits close to the ground during the morning were markedly different from the evening in open savanna, but not so in the riverine forest. There was evidence that droplets of .apprx. 80 .mu.m vmd penetrated more effectively than droplets of 150 .mu.m vmd, but a comparative evaluation of endosulfan applied at equivalent dosage rates (100 g/ha) and at these droplet sizes indicated both to be equally effective in reducing G. tachinoides during the first 2 wk following the applications. Deltamethrin applied as a fine spray at a dosage rate of 12.5 g/ha gave similar reductions of G. tachinoides. Studies of spray deposits within the habitat of the fly close to the ground and near the river''s edge suggested that there was insufficient insecticide on the target surfaces to give a persistent deposit. There is evidence that deposits increased with increasing height; the incidence of movement of tsetse flies during the might to resting sites within the upper parts of the riverine forest canopy may have bearing on control. The ability of aerial sprays to penetrate the riverine forest canopy is important in the different vegetation zones and is relevant in the more densely forested areas of the Southern Guinea Savanna zone where studies have yet to occur.