Tsetse flies choose birthing sites guided by environmental but not pheromonal cues

Tsetse flies significantly impact public health and economic development in sub-Saharan African countries by transmitting the fatal disease African trypanosomiasis. Unusually, instead of laying eggs, tsetse birth a single larva that immediately burrows into the soil to pupate. Where the female chooses to larviposit is therefore crucial for offspring survival. Previous studies showed that a putative larval pheromone, n-pentadecane, attracts gravid female Glossina morsitans morsitans to appropriate larviposition sites. However, this attraction could not be reproduced in field experiments. Here, we resolve this disparity by designing naturalistic laboratory experiments that closely mimic the characteristics found in the wild. We show that gravid tsetse were neither attracted to the putative pheromone nor, interestingly, to pupae placed in the soil. In contrast, females appear to choose larviposition sites based on environmental cues. We conclude that it is the substrate, rather than larval pheromones, which drives larviposition site selection under naturalistic conditions.