Publication Date

2016-12-11

Availability

Open access

Embargo Period

2016-12-11

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PHD)

Department

Ecosystem Science and Policy (Graduate)

Date of Defense

2016-09-15

First Committee Member

John C. Beier

Second Committee Member

Gina L. Maranto

Third Committee Member

Imelda K. Moise

Fourth Committee Member

Leon E. Hugo

Abstract

Now is a critical time for mosquito-borne disease (MBD) control. Although the reductions in the burden of malaria over the past decade and a half have saved more than a million lives, during the same period many mosquito-borne arboviruses have expanded in incidence and geographical range, causing large epidemics. With traditional mosquito control tools losing the battle against insecticide resistance and new biological control tools still in field trials, it is critical that MBD experts take a systematic approach to prepare for the future. The new biocontrol strategy of combating dengue fever with Wolbachia-infected Aedes aegypti is being tested at multiple field sites around the world, but the ecology of this group of bacteria in natural mosquito hosts remains largely unexplored. Hence, the evolutionary path of Wolbachia in the new host Ae. aeygpti is uncertain. In some Australian mosquito species with natural Wolbachia infections such as the container-breeder Aedes notoscriptus and saltmarsh inhabitant Culex sitiens, Wolbachia infection frequencies range from 25-85% and 50-100%, respectively. To investigate the ecology of Wolbachia in natural mosquito hosts, I colonized Cx. sitiens and Ae. notoscriptus from the field populations and monitored their Wolbachia infection frequencies for ten generations after establishment. I found that after colonization of these species, Wolbachia infection frequencies remained relatively constant over subsequent generations, with a portion of each population remaining uninfected. This persistent polymorphia in regards to Wolbachia infection could be due to environmental conditions during larval development or to mosquito host factors, such as other ovarian microbiota. I explored these possibilities in wild and caged Ae. aegypti, Ae. notoscriptus, Cx. sitiens populations. I found that Wolbachia infection levels were drastically reduced in Wolbachia-infected Ae. aegypti adult females after exposure to high temperatures during larval development, although the levels subsequently recovered to some extent once the heat was removed. I also found no association between Wolbahcia infection and the abundance of other bacterial species inhabiting the ovaries of Ae. aegypti and Cx. sitiens, suggesting that factors other than bacterial competition are likely responsible for regulating Wolbachia infection levels within mosquito ovaries. These findings shed light on potential futures for Wolbachia in MBD control. At the same time, I addressed critical policy issues relevant to the future by applying the methods of horizon scanning to the field of MBD control. Content analysis of twenty-five interviews with MBD experts and editorial-type scholarly articles was coupled with expert-formulated scenarios to form a forecast of the next twenty years of MBD control, including potential opportunities and threats. In addition to characterizing expert opinions on the current state of MBD, I identified eight drivers of change that could be influential in shaping the future of MBD control. I also described four sets of future scenarios for MBD control based on the input of experts. Overall, my work contributes key findings relating to Wolbachia ecology and MBD control policy that can be used to forecast and prepare for the future of MBDs.

Keywords

Vector control; Mosquito-borne diseases; Horizon scanning; Wolbachia

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