Phenotypic and genotypic analysis for quality control of Wolbachia-infected Aedes aegypti in a dengue biocontrol program

© 2014 Dr. Heng Lin YeapThe transinfection of the primary dengue vector, Aedes aegypti mosquitoes with the maternally-inherited, endosymbiotic bacterium, Wolbachia, causes dengue transmission attenuation in the mosquito. Since Wolbachia induces cytoplasmic incompatibility (the conditional sterility which renders uninfected females sterile when mated to Wolbachia-infected males), Wolbachia-infected mosquitoes became promising candidates for population replacement of field mosquitoes with non-dengue susceptible Wolbachia-infected Ae. aegypti. Multiple Wolbachia infections have been introduced into Ae. aegypti, but only two have been trialled in the field to date, the virulent life-shortening wMelPop “popcorn” strain (year 2012) and non-virulent wMel strain (years 2011, 2013, 2014). Both strain originated from Drosophila melanogaster. Despite extensive work on laboratory fitness testing, field fitness testing has only just begun as field trials commenced. This dissertation aims to study several fitness traits such as body size and mating competition, while also develop protocols for field monitoring of released mosquitoes and Wolbachia dynamics. Ultimately, I hope to provide an estimate of fitness and also provide a different perspective into assessment methods of estimating parameters related to Wolbachia dynamics. The dissertation will begin with morphometric assessments, in particular body size and shape, which were measured via wing centroid size, wing size/thorax length ratio and wing shape. The first study which took place during the wMel-infected mosquito release in 2011 aimed to monitor released mosquitoes in comparison with field uninfected mosquitoes. I also established whether the measured morphometric traits displayed a trend with oviposition site seeking frequency. I also demonstrated the possibility of using size and shape as a proxy to assess quality of released mosquitoes. In the second study, I assessed the wMelPop-infected mosquito release in 2012 via comparing the frequency of ovipositing released infected females and field uninfected females. I also determined whether morphometric traits affected oviposition frequency among the released females. In the third study, the co-occurrence of mitochondrial variation with Wolbachia was assessed to determine whether monitoring mitochondrial variation could aid in understanding Wolbachia dynamics in the field. I also provided an extension to available models to assess specific scenarios that might be encountered during a field release. Finally, I assessed whether Wolbachia infection (wMel-infection) impacted mating competition, specifically whether uninfected females possessed the ability to evade the cost of cytoplasmic incompatibility. I discuss implications of the results and recommendations for future monitoring