Tsetse flies (Glossina m. morsitans) choose birthing sites guided by substrate cues with no evidence for a role of pheromones

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 laboratory studies suggested 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 physical characteristics found in the wild. We show that gravid
G. m. morsitans 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 substrate
cues. We conclude that, among the many cues that likely contribute to
larviposition choice in nature, substrate features are a main determinant,
while we failed to find evidence of a role of pheromones.