Evaluation of improved coloured targets to control riverine tsetse in East Africa: A Bayesian approach

Abstract

Background Riverine tsetse (Glossina spp.) transmit Trypanosoma brucei gambiense which causes Gambian Human African Trypanosomiasis. Tiny Targets were developed for cost-effective riverine tsetse control, and comprise panels of insecticide-treated blue polyester fabric and black net that attract and kill tsetse. Versus typical blue polyesters, two putatively more attractive fabrics have been developed: Vestergaard ZeroFly blue, and violet. Violet was most attractive to savannah tsetse using large targets, but neither fabric has been tested for riverine tsetse using Tiny Targets. Methods We measured numbers of G. f. fuscipes attracted to electrified Tiny Targets in Kenya and Uganda. We compared violets, Vestergaard blues, and a typical blue polyester, using three replicated Latin squares experiments. We then employed Bayesian statistical analyses to generate expected catches for future target deployments incorporating uncertainty in model parameters, and prior knowledge from previous experiments. Results Expected catches for average future replicates of violet and Vestergaard blue targets were highly likely to exceed those for typical blue. Accounting for catch variability between replicates, it remained moderately probable (70–86% and 59–84%, respectively) that a given replicate of these targets would have a higher expected catch than typical blue on the same day at the same site. Meanwhile, expected catches for average violet replicates were, in general, moderately likely to exceed those for Vestergaard blue. However, the difference in medians was small, and accounting for catch variability, the probability that the expected catch for a violet replicate would exceed a Vestergaard blue equivalent was marginal (46–71%). Conclusion Violet and Vestergaard ZeroFly blue are expected to outperform typical blue polyester in the Tiny Target configuration. Violet is unlikely to greatly outperform Vestergaard blue deployed in this way, but because violet is highly attractive to both riverine and savannah tsetse using different target designs, it may provide the more suitable general-purpose fabric.

Multimodal interactions in Stomoxys navigation reveals synergy between olfaction and vision

“…The variation in attraction between various insects to the different fabric colors observed in this study shows insects' including hematophagous insects' preference for color and wavelength varies. In tsetse flies slight change in the blue fabric color and associated wavelength accompanied by significant catch difference demonstrating the importance of spectral intensity [10,12,63,64]. This variation in visual cues between insects may be caused by the differing numbers of ommatidia toward the detection of color, and light intensity, which might depend on the spectral sensitivities and interplay of the participating photoreceptors [65][66][67].…”

“…When we compare the natural deception system by those plants to be pollinated by insects without rewarding nectar the plants evolved to generate a perfect sensory impression in terms of smell, shape and even heat [13] [14] of a desirable host in the insect nervous system. However, in biting flies such as Stomoxys, tabanids and tsetse flies using a simple target and trap of blue color that does not look or smell like a cow, can easily catch a good number of hungry biting flies [10,11,[15][16][17][18][19].…”

“…Such behavior, i.e., the use of individual signal or minimum cue(s), reduction approach to represent a given host make insect vulnerable for deception. Insects make use of their visual signal to perform various behaviors, including flight control, object tracking for host or nectar-finding and have preference for certain bands from the visible spectrum inputs for their ecological interaction, including to get blood meal source and thus for disease transmission [7] [8][9][10][11][12]. When we compare the natural deception system by those plants to be pollinated by insects without rewarding nectar the plants evolved to generate a perfect sensory impression in terms of smell, shape and even heat [13] [14] of a desirable host in the insect nervous system.…”

Optimising the colour of traps requires an insect's eye view

“…In experiments on savannah tsetse, the new violet fabric attracted significantly more flies than a standard black target, whereas blue fabrics – including one specifically manufactured for tsetse targets – did not 21 . In follow‐up experiments on riverine tsetse, catches were more variable, but the greater attractiveness of the new violet fabric versus a typical blue fabric was still evident 22 …”