Satellite-based modelling of potential tsetse (Glossina pallidipes) breeding and foraging sites using teneral and non-teneral fly occurrence data

Abstract

Background African trypanosomiasis, which is mainly transmitted by tsetse flies (Glossina spp.), is a threat to public health and a significant hindrance to animal production. Tools that can reduce tsetse densities and interrupt disease transmission exist, but their large-scale deployment is limited by high implementation costs. This is in part limited by the absence of knowledge of breeding sites and dispersal data, and tools that can predict these in the absence of ground-truthing. Methods In Kenya, tsetse collections were carried out in 261 randomized points within Shimba Hills National Reserve (SHNR) and villages up to 5 km from the reserve boundary between 2017 and 2019. Considering their limited dispersal rate, we used in situ observations of newly emerged flies that had not had a blood meal (teneral) as a proxy for active breeding locations. We fitted commonly used species distribution models linking teneral and non-teneral tsetse presence with satellite-derived vegetation cover type fractions, greenness, temperature, and soil texture and moisture indices separately for the wet and dry season. Model performance was assessed with area under curve (AUC) statistics, while the maximum sum of sensitivity and specificity was used to classify suitable breeding or foraging sites. Results Glossina pallidipes flies were caught in 47% of the 261 traps, with teneral flies accounting for 37% of these traps. Fitted models were more accurate for the teneral flies (AUC = 0.83) as compared to the non-teneral (AUC = 0.73). The probability of teneral fly occurrence increased with woodland fractions but decreased with cropland fractions. During the wet season, the likelihood of teneral flies occurring decreased as silt content increased. Adult tsetse flies were less likely to be trapped in areas with average land surface temperatures below 24 °C. The models predicted that 63% of the potential tsetse breeding area was within the SHNR, but also indicated potential breeding pockets outside the reserve. Conclusion Modelling tsetse occurrence data disaggregated by life stages with time series of satellite-derived variables enabled the spatial characterization of potential breeding and foraging sites for G. pallidipes. Our models provide insight into tsetse bionomics and aid in characterising tsetse infestations and thus prioritizing control areas. Graphical abstract

Evidence-based advice on timing and location of tsetse control measures in Shimba Hills National reserve, Kenya

“…While rainfall may not have a direct impact on certain aspects of tsetse activities, such as larval development or production rate, it can indirectly affect the dynamics of tsetse populations. For example, rainfall often leads to an increase in vegetation cover, which is crucial for tsetse breeding and resting [ 12 , 24 ]. This might explain why tsetse numbers in distant traps rose in tandem with increasing NDVI values shortly after the start of the rainy season.…”

Transcriptomic Profiling of Trypanosoma Congolense Mouthpart Parasites from Naturally Infected Flies

“…It appears that vector biology may play a large role in parasite expression pro les, be it in terms of the tsetse genetic background, or its microbiome. In the Shimba Hills National Reserve, tsetse ies of the species Glossina pallidipes predominate [31,32], while the ies examined in previous studies were Glossina morsitans morsitans [5,26]. Moreover, laboratory-infected ies are always infected as teneral (i.e.…”

“…Moreover, laboratory-infected ies are always infected as teneral (i.e. newly emerged, previously unfed), whereas in the Shimba Hills National Reserve, a previous study estimated that only approximately 37% of the infected tsetse ies are young adults [31]. It is well described that teneral ies are more susceptible to trypanosome infections [33].…”

Evaluating the efficacy of various traps in catching tsetse flies at Nech Sar and Maze National Parks, Southwestern Ethiopia: An Implication for Trypanosoma Vector Control

“…This could probably be due to the fact that WGL are suitable for the reproduction of G. pallidipes and their propagation, as WGL provides shade and humid habitats [23]. To that end, Nech Sar Park, where over 82% of tsetse flies were caught, has an annual temperature ranging from 20˚C to 34˚C which corresponds to the range of temperature required for the general survival and breeding of tsetse flies and for the third instar larva to fully grow or change into a pupa stage [23]. This could serve as practical evidence of the importance of climate and vegetation in determining the distribution of tsetse flies [24].…”