The fungal communities of mosquitoes and their impact on mosquito survival

Abstract

Mosquitoes, including the Asian tiger mosquito, Aedes albopictus, and the African malaria mosquito, Anopheles gambiae, are of public health concern due to the ability of female mosquitoes to transmit disease-causing pathogens during blood-feeding. Mosquito larvae inhabit natural and artificial aquatic habitats, where they interact with numerous microorganisms that assemble into microbial communities. The bacterial communities (i.e., microbiota) of mosquito larvae play a profound role in mosquito physiology and vector competence. In addition to bacteria, mosquitoes also interact with fungi in their habitats through surface contact and ingestion. Some yeasts provide nutritional and physiological cues for mosquito development, while other fungi act as entomopathogens to mosquito larvae and adults. However, little is known about mosquito-associated fungal communities and the factors that drive their assembly in mosquito larvae. In this dissertation, I aimed to determine (1) the fungal communities associated with mosquito larvae and their aquatic habitats, (2) the drivers of fungal community assembly in mosquito larvae, and (3) the impact of mosquito-isolated fungi on mosquito fitness. To address the first two aims, I used metabarcode sequencing of the Internal Transcribed Spacer 2 (ITS2) marker to identify fungal taxa and compared diversity indices to identify the drivers of their assembly in mosquito larvae. In addition, to address the third aim, I used culture-based approaches to isolate mosquito-associated fungi and assess their impact on mosquito survival and development. Using the data generated by ITS2 sequencing, I determined that fungal communities of mosquito larvae largely reflect those of their habitats with no evidence of environmental filtering in mosquito guts. In addition, I showed differences in fungal communities between mosquito guts and carcasses driven by mosquito feeding behavior and fungal ecology. Using laboratory-based microcosm assays, I identified disparate fungal communities across Ae. albopictus life stages. These differences were not attributed to changes in fungal communities of their aquatic habitats, indicating that mosquito ontogeny acts as an environmental filter for fungal communities in Ae. albopictus larvae. Using culture-based approaches, I isolated nine fungi from Ae. albopictus larvae. One of these fungi, a new isolate of Beauveria bassiana, was a potent mosquito larvicide of An. gambiae but not Ae. albopictus. Larval exposure to this B. bassiana isolate delayed development to adulthood in both mosquito species, which further reduced mosquito population growth of An. gambiae and also Ae. albopictus, albeit to a lesser degree. Taken together, this dissertation contributes to fundamental knowledge of mosquito vector ecology. It provides the first comprehensive characterization of mosquito-associated fungal communities, which are driven largely by habitat and to a lesser degree by mosquito feeding behavior and ontogeny, as well as fungal ecology. Furthermore, this dissertation contributes to efforts in vector control by establishing a reproducible laboratory-based experimental design to evaluate potential biolarvicides for mosquito control.