The impact of insecticide resistance and parasite infection on vector behaviour

Vector control remains one of the most important methods for reducing insect-borne diseases across the globe. However, heavy reliance on insecticides has led to the rapid spread of insecticide resistance, threatening the operational success of control programmes. In response to concerns over the sustained efficacy of our current tools, novel insecticides and products are now in development and various next generation bednets are now in widespread use across Africa to combat resistance and restore ITN effectiveness. Understanding how resistance and new control methods may alter vector-specific disease transmission parameters is crucial. While insecticide resistance and parasite infection rates are documented in many populations, their effect on mosquito life-history traits and behaviour is less understood. This thesis aimed to assess the impact of insecticide resistance and parasite infection on mosquito fitness and behaviour and how changes in either could impact the efficacy of new control tools and vectorial capacity. This was achieved through work that 1) quantified and mapped insecticide resistance in Africa to document the spread of resistance in malaria vectors and the role of different resistance mechanisms, 2) evaluated next-generation ITNs for reducing malaria prevalence, 3) measured the impact of insecticide resistance on mosquito behavioural responses to ITNs and 4) studied the impact of exposure to insecticides and parasite infection on mosquito behaviour and longevity. The results present data collated on the spatial distribution of insecticide resistance phenotypes and genotypes, which can be used to guide control programmes in resistance monitoring and consider changes in bed net distribution. The analysis generated by a systematic review showed that next-generation pyrethroid-PBO nets increase mosquito mortality, reduce blood-feeding success and lower clinical malaria incidence in areas with high insecticide resistance. Room-scale video tracking of mosquitoes around these next-generation nets has enabled us to investigate how these ITNs worked, capturing data showing the effects on mosquito behaviour of a number of different ITNs are remarkably consistent, with no significant differences in the responses between strains of different pyrethroid susceptibility to different net treatments. Laboratory studies have explained how insecticide selection impacted mosquito fitness in male and female mosquitoes, demonstrating trade-offs in life-history traits that could limit or enhance disease transmission. It was also demonstrated that mosquitoes exposed to parasitic infection show a dynamic, stage-specific and density-dependent change in behaviour to host cues, decreased flight ability and reduced energy resources. Incorporating knowledge on the spread of insecticide resistance, the effects of next-generation nets on mosquito mortality and behaviour, and the impacts of resistance and infection on mosquito physiology will lead to a more holistic understanding of the impact of new vector control tools on mosquito-transmitted diseases