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

Abstract

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. By 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 for a role of pheromones.

Identification of Semiochemical Candidates Involved in Glossina Palpalis Gambiensis Larviposition Site Selection and Behavioural Responses of Adult Gravid Females

“…In the eld, larval aggregation as a consequence of females larviposition behaviour has been observed especially in species of the Palpalis group in West Africa (Buxton 1955;Salou et al 2022). In laboratory, site selection has been shown to be driven by some physical factors, such as shade, colour, soil texture, and composition (Parker 1956; Rowcliffe and Finlayson 1981;Adden et al 2023) but are not su ciently speci c to explain why, in the eld, numerous pupae are found at the same breeding site, sometimes in association with other tsetse ies species (Buxton 1955;Salou et al 2022). The existence of an aggregation factor was suggested as early as in the 1950s (Buxton 1955;Nash 1969) In Glossina morsitans morsitans (Wiedemann, 1830), chemical volatiles from larval origin have been identi ed (n-pentadecane and n-dodecane) and their behavioural attraction/activity demonstrated in the laboratory (Saini et al 1996).…”