Dispersal in heterogeneous environments drives population dynamics and control of tsetse flies

Abstract

Spatio-temporally heterogeneous environments may lead to unexpected population dynamics. Knowledge is needed on local properties favouring population resilience at large scale. For pathogen vectors, such as tsetse flies transmitting human and animal African trypanosomosis, this is crucial to target management strategies. We developed a mechanistic spatio-temporal model of the age-structured population dynamics of tsetse flies, parametrized with field and laboratory data. It accounts for density- and temperature-dependence. The studied environment is heterogeneous, fragmented and dispersal is suitability-driven. We confirmed that temperature and adult mortality have a strong impact on tsetse populations. When homogeneously increasing adult mortality, control was less effective and induced faster population recovery in the coldest and temperature-stable locations, creating refuges. To optimally select locations to control, we assessed the potential impact of treating them and their contribution to the whole population. This heterogeneous control induced a similar population decrease, with more dispersed individuals. Control efficacy was no longer related to temperature. Dispersal was responsible for refuges at the interface between controlled and uncontrolled zones, where resurgence after control was very high. The early identification of refuges, which could jeopardize control efforts, is crucial. We recommend baseline data collection to characterize the ecosystem before implementing any measures.

X-rays are as effective as gamma-rays for the sterilization of Glossina palpalis gambiensis Vanderplank, 1911 (Diptera: Glossinidae) for use in the sterile insect technique

“…Other results indicated an overall propensity of 0.57 with G. brevipalpis 32 , while 0.63 and 0.41 were obtained with G. austeni 39 . These dissimilarities may be a result of a difference in treatments and environmental conditions as fly behaviour is indeed influenced by these 63 . However, the relative mating index indicates that the irradiated males are still competitive, and the small deficit as compared with non-irradiated male flies can be mitigated in SIT programmes by an increase in the sterile to wild male ratio.…”

Modelling the spatial and temporal distribution of tsetse flies for targeted control

“…In the Niayes area in Senegal, a recent study applied a spatial-temporal mechanistic model utilizing satellite-derived environmental data and key knowledge about tsetse biology. The findings revealed that only 4% of the land in Niayes is deemed suitable for tsetse occurrence (Cecilia et al, 2021), which is considerably less than the previously predicted suitability based on the continental tsetse distribution maps (Wint, 2003). In Zambia, recent predictions based on maximum-entropy modelling, and a series of satellite-based predictors indicate a decline in the area coverage of Glossina morsitans morsitans and Glossina morsitans centralis by 47% and 29%, respectively, compared to their historical distribution (Muyobela et al, 2023).…”

“…While these maps were updated twenty years ago, they suffer from a coarse resolution (5x5 km), and their accuracy remains uncertain (Wint, 2003). Local studies have indicated significant disparities between these maps and the actual occurrence of the fly (Esterhuizen et al, 2005;Cecilia et al, 2021), highlighting the pressing need for more accurate and fine-scale mapping approaches. This challenge for improved information and fine-scale mapping extends to tsetse abundance, where there are no available continental maps, and local-scale studies focused on quantifying tsetse abundance are scarce.…”

“…However, in most regions of sub-Saharan Africa, the available maps were developed at a low spatial resolution of 5km by 5km between 1999 and 2003 (Wint, 2003). Local research has revealed significant discrepancies between those maps and the actual presence of the fly (Esterhuizen et al, 2005;Cecilia et al, 2021;Gachoki et al, 2021), raising questions about their reliability. Large-scale tsetse surveillance using traps is costly and time-consuming, making it hard to gather detailed ground data for predicting suitable habitats for tsetse flies in Africa.…”