How Do Bacterial Symbionts in the Larval Environment Affect Culex Quinquefasciatus Development?

Abstract

Hawaiian honeycreepers, a group of forest birds endemic to the Hawaiian Islands, are facing rapid population declines due to avian malaria, a non-native disease caused by the parasite, Plasmodium relictum. Culex quinquefasciatus, an invasive mosquito species, serves as the primary vector of avian malaria, transmitting the disease among these endemic birds. Mosquitoes rely heavily on microbial associations that shape their physiology, survival, and reproductive success, yet little is known about how larval environment microbes influence their performance in the environment. This thesis investigates how bacterial symbionts introduced in larval environments influence the developmental success of Culex quinquefasciatus (Cq). Developmental metrics (e.g., survival, time to pupation) were measured to test the hypotheses that Thorsellia and Aeromonas, two microbial taxa that are abundant and prevalent symbionts of Cq mosquitoes in the wild, enhance larval development. The microbial compositions were manipulated across six treatments by keeping Thorsellia and Aeromonas alive or heat-killing them in different combinations. This design tested whether larval development was enhanced by Thorsellia alone, by Aeromonas alone, or by a microbial partnership between the two—versus effects caused by the core microbiome. Microbial environments composed of synthetic communities generally had reduced larval developmental success, relative to the non-axenic control. However, the impact of Thorsellia in driving this effect is confounded by the unique presence of other microbes in the control treatment. Cumulatively, this study provides a refined list of wild-associated microbial taxa that were associated with improved Cq developmental success. By dissecting how specific microbial compositions affect mosquito fitness, this study can improve the mass-rearing of high-quality mosquitoes for incompatible insect technique (IIT) programs in Hawai‘i and contribute to efforts to protect endangered Hawaiian honeycreepers from avian malaria.