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

Abstract

Riverine tsetse transmit the parasites that cause the most prevalent form of human African trypanosomiasis, Gambian HAT. In response to the imperative for cheap and efficient tsetse control, insecticide-treated ‘tiny targets’ have been developed through refinement of tsetse attractants based on blue fabric panels. However, modern blue polyesters used for this purpose attract many less tsetse than traditional phthalogen blue cottons. Therefore, colour engineering polyesters for improved attractiveness has great potential for tiny target development. Because flies have markedly different photoreceptor spectral sensitivities from humans, and the responses of these photoreceptors provide the inputs to their visually guided behaviours, it is essential that polyester colour engineering be guided by fly photoreceptor-based explanations of tsetse attraction. To this end, tsetse attraction to differently coloured fabrics was recently modelled using the calculated excitations elicited in a generic set of fly photoreceptors as predictors. However, electrophysiological data from tsetse indicate the potential for modified spectral sensitivities versus the generic pattern, and processing of fly photoreceptor responses within segregated achromatic and chromatic channels has long been hypothesised. Thus, I constructed photoreceptor-based models explaining the attraction of G. f. fuscipes to differently coloured tiny targets recorded in a previously published investigation, under differing assumptions about tsetse spectral sensitivities and organisation of visual processing. Models separating photoreceptor responses into achromatic and chromatic channels explained attraction better than earlier models combining weighted photoreceptor responses in a single mechanism, regardless of the spectral sensitivities assumed. However, common principles for fabric colour engineering were evident across the complete set of models examined, and were consistent with earlier work. Tools for the calculation of fly photoreceptor excitations are available with this paper, and the ways in which these and photoreceptor-based models of attraction can provide colorimetric values for the engineering of more-attractively coloured polyester fabrics are discussed.

Optimising targets for tsetse control: Taking a fly’s-eye-view to improve the colour of synthetic fabrics

“…Cheap and effective devices for tsetse control, such as artificial baits [4, 5], can help manage these diseases. There is now considerable scope for improving these baits through the use of robust modern synthetic materials and by physiologically inspired approaches to assess and improve the attractiveness of colours as flies see them [6–8].…”

“…Thus, a rational approach to the engineering of coloured polyesters for tsetse targets must focus on these relevant channels of sensory information, rather than human colour descriptions or raw reflectance spectra [7]. To this end, tools to calculate fly photoreceptor responses from the measured reflectance spectra of fabrics were developed [7, 8]. Using these tools, fly photoreceptor excitation values were calculated for the coloured fabrics tested in several large field studies on riverine and savannah tsetse species [6, 13, 17], and statistically related to tsetse attraction recorded in those studies [7, 8] (c.f.…”

“…To this end, tools to calculate fly photoreceptor responses from the measured reflectance spectra of fabrics were developed [7, 8]. Using these tools, fly photoreceptor excitation values were calculated for the coloured fabrics tested in several large field studies on riverine and savannah tsetse species [6, 13, 17], and statistically related to tsetse attraction recorded in those studies [7, 8] (c.f. [20, 21]).…”

“…These photoreceptor-based models can be used to evaluate fabrics theoretically, which is important as control operations reduce fly numbers and make extensive field-testing difficult. More importantly, because it is possible to determine the reflectance spectra that would result from particular dye recipes theoretically [22], these can be evaluated and refined in silico [8]. In this way, the deliberate engineering of polyester fabrics for improved attractiveness to tsetse is possible.…”

“…Photoreceptor-based models statistically relate fly photoreceptor responses calculated from the reflectance spectra of coloured fabrics to the numbers of tsetse caught at traps and targets constructed from those fabrics. These models suggest that photoreceptor R7y contributes positively to tsetse attraction, while photoreceptors R7p and R8y contribute negatively [7, 8]. Such models provide a means to evaluate and refine the fly-relevant colour properties of fabrics for tsetse targets.…”