Optimizing the Colour and Fabric of Targets for the Control of the Tsetse Fly Glossina fuscipes fuscipes

Abstract

BackgroundMost cases of human African trypanosomiasis (HAT) start with a bite from one of the subspecies of Glossina fuscipes. Tsetse use a range of olfactory and visual stimuli to locate their hosts and this response can be exploited to lure tsetse to insecticide-treated targets thereby reducing transmission. To provide a rational basis for cost-effective designs of target, we undertook studies to identify the optimal target colour.Methodology/Principal FindingsOn the Chamaunga islands of Lake Victoria , Kenya, studies were made of the numbers of G. fuscipes fuscipes attracted to targets consisting of a panel (25 cm square) of various coloured fabrics flanked by a panel (also 25 cm square) of fine black netting. Both panels were covered with an electrocuting grid to catch tsetse as they contacted the target. The reflectances of the 37 different-coloured cloth panels utilised in the study were measured spectrophotometrically. Catch was positively correlated with percentage reflectance at the blue (460 nm) wavelength and negatively correlated with reflectance at UV (360 nm) and green (520 nm) wavelengths. The best target was subjectively blue, with percentage reflectances of 3%, 29%, and 20% at 360 nm, 460 nm and 520 nm respectively. The worst target was also, subjectively, blue, but with high reflectances at UV (35% reflectance at 360 nm) wavelengths as well as blue (36% reflectance at 460 nm); the best low UV-reflecting blue caught 3× more tsetse than the high UV-reflecting blue.Conclusions/SignificanceInsecticide-treated targets to control G. f. fuscipes should be blue with low reflectance in both the UV and green bands of the spectrum. Targets that are subjectively blue will perform poorly if they also reflect UV strongly. The selection of fabrics for targets should be guided by spectral analysis of the cloth across both the spectrum visible to humans and the UV region.

Genome Sequence of the Tsetse Fly ( Glossina morsitans ): Vector of African Trypanosomiasis

“…Most important, the recovery of opsin Rh5 indicates the likely presence of blue-sensitive R8p photoreceptors in Glossina that have been missed in experimental studies (33). This finding is consistent with tsetse’s attraction to blue/black, which has been widely exploited for the development of traps to reduce vector populations (37). It is further notable that the study of opsin conservation and expression in the blow fly retina recovered the same four opsin paralogs (38), suggesting that the deployment of a single ultraviolet (UV)–sensitive opsin ( Rh3 ) represents the ground state for calyptrate Diptera, in contrast to the expression of two UV-sensitive opsins ( Rh3 and Rh4 ) in the eyes of Drosophila .…”

Developing photoreceptor-based models of visual attraction in riverine tsetse, for use in the engineering of more-attractive polyester fabrics for control devices

“…Therefore, concerted efforts have been underway to improve the cost and efficiency of control devices for riverine tsetse so that they might contribute to efforts to eliminate Gambian HAT (e.g. [10,11,12,13,14,15,16]).…”

“…Instead, narrow and densely vegetated riverine habitats mean that odour plumes are of limited utility in host seeking, and the reduced probability of encountering hosts in such habitats necessitates less selectivity when one is encountered [7,17]. Identification of these crucial behavioural differences has allowed the development of ‘tiny targets’ for riverine tsetse, which comprise a 0.25 m x 0.25 m blue polyester panel adjacent to a 0.25 m x 0.25 m black polyethylene mosquito net panel, with both panels impregnated with deltamethrin insecticide [5,10,12,14]. The blue fabric panel serves to attract tsetse, whilst the mosquito net panel is thought to intercept circling flies, overcoming their reduced tendency to alight directly on small visual targets [12].…”

“…Multiple large scale field studies pre-dating the development of tiny targets established that colour was an important determinant of tsetse attraction, and that phthalogen blue-dyed cotton was highly attractive to tsetse [8,14,18,19]. Phthalogen blue cotton is now reportedly difficult to obtain, whilst polyester is the material of choice for tiny targets because it is lighter, more robust under field conditions, and holds insecticide more effectively [14].…”

“…Multiple large scale field studies pre-dating the development of tiny targets established that colour was an important determinant of tsetse attraction, and that phthalogen blue-dyed cotton was highly attractive to tsetse [8,14,18,19]. Phthalogen blue cotton is now reportedly difficult to obtain, whilst polyester is the material of choice for tiny targets because it is lighter, more robust under field conditions, and holds insecticide more effectively [14]. Although the blue polyester used in tsetse control devices is sometimes referred to as ‘phthalogen blue’ polyester, phthalogen blue dye can only be applied to cotton, and the reflectance spectra of such polyester fabrics differ subtly from that of the original cotton material [14,20].…”