The bio-ecology of key mosquito vector species in Botswana: implications for shifting environments

Abstract

Mosquitoes account for significant morbidity and mortality globally, with the African region being most affected. In many arid regions, including Botswana, mosquitoes are increasingly becoming problematic, harbouring pathogens and parasites that cause debilitating infectious diseases to differential host species. The risk of mosquito proliferation and burden is accelerated when affected societies have knowledge gaps coupled with climatic mediated global change scenarios. In Botswana mosquito research is skewed towards malaria and associated anopheline vector species, neglecting other mosquito taxa, despite their economic significance as disease vectors for humans, domestic animals and wildlife. The national vector control programme in the country is mainly focused on adult mosquito species with management of juveniles (e.g., larvae) largely disregarded. Cognisant of these shortcomings, the thesis was thus aimed at bridging knowledge gaps in mosquito bio-ecology within the Central district, Botswana, a largely neglected region on vector mosquito bio-ecology. Knowledge, attitude and practices of local communities were assessed on mosquitoes across sub-districts of malaria endemic and non endemicity status, with communities largely exhibiting limited knowledge on aspects of mosquito bio-ecology. Mosquito communities across the region were also assessed with key taxa species of medical (Anopheles, Aedes and Culex species) and veterinary (Culiseta longiareolata) importance identified throughout the study areas. The study also reports for the first time in the country, a globally important and medically significant invasive vector species, Ae. aegypti from Palapye sub-district. Using a mesocosm approach, the effects of anthropogenic activities were tested on mosquito breeding. The degradation associated with cattle dung nutrification in aquatic environments favoured oviposition by mosquito vector species. With the aim to assess natural predator (Lovenula falcifera and Anisops sardea) mosquito control potential, their predation on larvae of the abundant mosquito species (Culex pipiens) were quantified using a functional response (FR) approach. Both predators exhibited Type II FRs and typically contributed additively to prey risk, with synergistic impacts evident on prey of intermediate sizes. In complementing this approach, multiple predator effects by notonectid predators, A. sardea and Enithares chinai, were quantified across a habitat complexity gradient. Enithares chinai exhibited significantly greater consumption rates than A. sardea, both as individuals and conspecific pairs. Each predator type displayed Type II FRs across experimental treatments, with synergistic multiple predator effects displayed in the absence of habitat complexity. Effects of increasing habitat complexity modified multiple predator effects differentially between species given behavioral differences. Whilst the ecosystem services provided by natural predators for mosquito biological control are evident, understanding how climate change-induced environmental perturbations may corrode these services remains largely unknown. Here, critical thermal limits of key predator-prey participants across instar stages (as above) were explored. All predators generally had lower activity limits and narrower thermal windows compared to their larval mosquito prey. These results point to significant predator-prey mismatches under environmental change, potentially adversely affecting natural mosquito biocontrol given projected shifts in temperature fluctuations in the study region. The information gleaned from the various chapters will be useful for practitioners dealing with the various human, biological and ecological components of pest mosquito control and emerging threats in the region.