Wolbachia infection dynamics and applied vector-borne disease control in mosquitoes

The maternally-inherited symbiont Wolbachia is associated with host reproductive abnormalities including cytoplasmic incompatibility (reduced egg hatch when infected males mate with uninfected females). Strategies exploiting Wolbachia been proposed for vector-borne disease control and pest population suppression. The focus of this research was to investigate Wolbachia infection in natural mosquito populations and develop novel strategies for vector-borne disease control.; Fourteen species of North American mosquitoes encompassing the genera Aedes, Anopheles, Culiseta, Culex and Ocherlotatus were assayed for Wolbachia infection, with focus on important Californian vector and pest species. Only members of the Culex pipiens species complex were infected. The infection was identified by molecular methods as the Wolbachia strain wPip.; Strain-specific PCR, Wolbachia wsp gene sequencing and crossing experiments indicated that a single Wolbachia strain infects California Culex pipiens complex mosquitoes. Infection frequency in 14 populations along a north-south cline was assayed for 2 years; infection was near or at fixation in all populations. Wolbachia transmission parameters were quantified under lab and field conditions. Model predictions based on field data accurately predicted infection equilibrium levels in natural populations. This is the first time Wolbachia infection dynamics have been determined for a vector insect in nature.; Current transgenic strategies for vector-borne disease control focus on vector susceptibility to pathogen infection and/or transmission, which is an inefficient target for pathogen transmission interference. Manipulation of vector survival is theoretically more effective, resulting in larger reductions in the expected number of human infections. A hypothetical method to manipulate vector survival is to drive mortality-inducing Wolbachia into populations. For varying patterns/degrees of induced mortality, I outline the conditions under which virulent Wolbachia introductions into vector populations are expected to succeed and quantify resultant reductions in pathogen transmission. For successful introductions, induced mortality must be delayed until after vector reproduction begins. If this condition is not met, introduction thresholds become too high to be economically/logistically feasible. Under proper circumstances, symbiont-induced manipulation of vector survival can theoretically result in up to 100% reduction in pathogen transmission, depending on Wolbachia parameters, magnitude/pattern of induced mortality, and duration of pathogen incubation in the vector.