Abstract
The savannah tsetse flies, Glossina morsitans morsitans and G. pallidipes, are important vectors of Rhodesian human African trypanosomiasis and animal African trypanosomiasis in East and southern Africa. We tested in Zimbabwe whether robust, synthetic fabrics, and innovative fly’s-eye-view approaches to optimise fabric colour, can improve insecticide-treated targets employed for tsetse control. Flies were caught by electrocution at a standard target comprising a 1m x 1m black cotton cloth panel with 1m x 0.5m black polyester net panels on each side. Catches were subdivided by species and sex. Tsetse catches were unaffected by substitution of the black cotton with a blue polyester produced for riverine tsetse targets. Exchanging the net panels for phthalogen blue cotton to simulate the target routinely used in Zimbabwe significantly reduced catches of female G. m. morsitans (mean catch 0.7 times that at standard), with no effect on other tsetse catches. However, significantly greater proportions of the catch were intercepted at the central panel of the Zimbabwe (means 0.47–0.79) versus standard designs (0.11–0.29). We also engineered a new violet polyester cloth using models of tsetse attraction based upon fly photoreceptor responses. With and without odour lure, catches of females of both species at the violet target were significantly greater than those at standard (means 1.5–1.6 times those at standard), and typical blue polyester targets (means 0.9–1.3 times those at standard). Similar effects were observed for males under some combinations of species and odour treatment. The proportions of catch intercepted at the central panel of the violet target (means 0.08–0.18) were intermediate between those at standard and typical blue polyester. Further, the reflectance spectrum of violet polyester was more stable under field conditions than that of black cotton. Our results demonstrate the effectiveness of photoreceptor-based models as a novel means of improving targets to control tsetse and trypanosomiases.
Highlights
Tsetse flies (Glossina spp.) infest an estimated 10 million km2 of sub-Saharan Africa, and their bites transmit trypanosome parasites that inflict a significant disease burden on rural communities
Tsetse can be controlled using insecticide-treated fabric targets, which are typically blue or black and traditionally made of cotton. The efficiency of these targets might be improved by using modern synthetic fabrics that last longer and hold insecticide better, and by optimising the colour of these fabrics to be more attractive to tsetse
We found that a blue polyester currently produced for riverine tsetse targets was as effective in attracting tsetse as standard cotton targets, demonstrating that these more robust polyesters can be used for savannah tsetse control
Summary
Tsetse flies (Glossina spp.) infest an estimated 10 million km of sub-Saharan Africa, and their bites transmit trypanosome parasites that inflict a significant disease burden on rural communities. Control of the riverine tsetse that transmit g-HAT has not traditionally been recommended, but it is acknowledged that it can make an important contribution to tackling the disease provided costs are kept low [10]. This imperative for high costeffectiveness has spurred detailed investigation of the visually guided behaviour of tsetse, and the development of ‘Tiny Targets’ comprising smaller, lighter and more robust panels of blue polyester [6, 11, 12]
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