Effect of zebra skin-derived compounds on field catches of the human African trypanosomiasis vector Glossina fuscipes fuscipes

The riverine tsetse fly Glossina fuscipes fuscipes is a major vector of trypanosome pathogens causing African trypanosomiasis. This fly species uses a combination of olfactory and visual cues to locate its hosts. Previously, traps and targets baited with visual cues have been used in vector control, but the development of olfactory based tools has been challenging. Recently, repellents have shown promise as olfactory-based tools in tsetse vector control. Here, we evaluated a three-component blend comprising 6-methyl-5-hepten-2-one, acetophenone and geranyl acetone (blend K), previously identified as a repellent for savannah tsetse flies in zebra skin odor, on G. f. fuscipes populations. Using a series of 6 x 6 randomized Latin square-designed experiments, G. f. fuscipes catches in biconical traps were monitored on four islands of Lake Victoria in western Kenya between July and September 2019, after the long rainy season. Traps were baited with blend K and individual components of this blend. The known tsetse repellent blend WRC (waterbuck repellent compounds) and trap alone were included as controls. Daily catch data in thirty-six replicate trials were analyzed using generalized linear model with negative binomial error structure using the package "MASS" in R. Treatment, day and site were set as predictor variables. Our results showed that, blend K significantly reduced G. f. fuscipes catches by 25.6% (P < 0.01) compared to the control trap alone but was not significantly different from WRC which reduced catches by 20.7% (P < 0.05). Of the individual compounds, geranyl acetone solely significantly reduced catches by 29.1% (P < 0.01) which did not differ from blend K or WRC. We conclude that geranyl acetone accounts for the repellent effect of blend K on the riverine tsetse fly, G. f. fuscipes, demonstrating the ecological importance of animal skin odors in the host seeking behavior of medically-important tsetse fly vectors.