| Summary: | <p>Insects pose large problems for health and agriculture; several major diseases are transmitted by insect vectors, and huge losses in food production occur due to insect pests. Current strategies for insect control are inadequate, with several disadvantages. Various novel approaches are being developed, aimed at either suppressing wild populations, or replacing them with insects refractory to disease-causing pathogens.</p> <p>Some possible strategies utilise <em>Wolbachia</em>, a genus of maternally inherited intracellular bacteria. <em>Wolbachia</em> can manipulate host reproduction through a phenomenon known as cytoplasmic incompatibility (CI), which leads to spread of <em>Wolbachia</em> through populations. CI could potentially be used as a gene drive system for spread of pathogen-resistance genes, or for population suppression via the release of incompatible males. Furthermore, some strains of <em>Wolbachia</em> have been found to inhibit virus transmission by mosquitoes; there have been successful field trials of population replacement exploiting this inhibition.</p> <p>At present, little is known about the mechanisms of CI, or viral inhibition by <em>Wolbachia</em>. Discussed in Chapter 2, candidate genes for CI involvement were identified by sequencing the genome of the non-CI strain wAu and comparing it to that of the CI strain wMel. One candidate was used to transform <em>Drosophila melanogaster</em>, but it did not induce a CI phenotype. Chapter 3 discusses further identification and investigation of candidate genes for CI involvement by comparing RNA-seq data from wAu and the CI strain wRi, and from <em>D. simulans</em> either uninfected or infected with one of these two strains. Similarly, candidate genes for viral inhibition were identified and investigated by comparing RNA-seq data from <em>Aedes albopictus</em> mosquitoes that were uninfected, naturally infected with wAlb, or transinfected with wMel, which inhibits dengue in this species.</p> <p>Other potential insect control strategies involve the release of modified insects with a genetic system that leads to population suppression. Discussed in Chapter 4, attempts were made using comparative genomics to identify the sex-determining locus in the mosquito <em>Ae. aegypti</em>, which could be utilised in genetic control systems. Some possible regions were identified, but the locus was discovered by another group before the work was completed. Chapter 4 also discusses the identification using RNA-seq of germline-specifically expressed or spliced genes in <em>Ae. aegypti</em> and the agricultural pest <em>Ceratitis capitata</em>; these could be used to control gene expression in various genetic insect control systems.</p> <p>Overall this thesis demonstrates the use of high-throughput sequencing analyses to identify and investigate candidate genes of importance to insect control. It will hopefully serve as a platform for further research in this important field.</p>
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