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

Roger D Santer

doi:10.1371/journal.pntd.0005448

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.

Highlights

Tsetse flies (Glossina spp.) are blood-feeding flies of sub-Saharan Africa, and their bites transmit the trypanosome parasites that cause sleeping sickness in humans, and nagana in cattle [1]
Tsetse control can contribute to disease control thanks to cheap and efficient ‘tiny targets’ that attract tsetse using a panel of blue fabric, a highly attractive colour for the flies
It will be possible to engineer more-attractive polyesters using techniques based on those already employed for fabric colour matching to the human eye

Summary

Introduction

Tsetse flies (Glossina spp.) are blood-feeding flies of sub-Saharan Africa, and their bites transmit the trypanosome parasites that cause sleeping sickness in humans (human African trypanosomiasis, HAT), and nagana in cattle (animal African trypanosomiasis, AAT) [1]. 2%) comprise an acute disease termed Rhodesian HAT that occurs in Eastern and Southern Africa [1] 98%) comprise a chronic disease termed Gambian HAT that occurs in Central and Western Africa [1] This form of the disease is caused by T. b. Unlike Rhodesian HAT, Gambian HAT is considered an anthroponosis, and case detection and treatment programmes are the predominant method of disease control. This is because control methods developed for savannah tsetse are not cost effective or logistically feasible for the control of riverine tsetse in remote, rural locations, and where cattle rearing densities are low [3,4,6]. Has proved effective in reducing tsetse numbers below those

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