Effects of Larval Exposure to Bacterial Species in Three Genera on Life History Traits and Oviposition Behavior in the Southern House Mosquito, Culex quinquefasciatus

The biofilm is the most common niche for microorganisms living in aquatic environments. Forming a biofilm provides the means to resist shear forces, adverse osmolarity, chemical agents, and other environmental stressors. Biofilms also provide a major food source for aquatic arthropods like mosquito larvae. Culex quinquefasciatus larvae are found in freshwater pools with high organic content, and have the ability to graze on bacterial biofilms. To study how C. quinquefasciatus mosquitoes interact with bacteria in their environment I developed an experimental system that allows mosquito larvae to freely graze on bacteria in either the planktonic or biofilm state. The efficacy of this system was confirmed via fluorescent microscopy for five species of biofilm-forming bacteria (Francisella tularensis LVS, Francisella novicida, Pseudomonas aeruginosa, Legionella pneumophila, and Legionella rubriluscens), and a PCR protocol was developed to confirm the presence of bacteria in exposed larvae. The model was then used to assess mosquito development time, survival, wing length, and fecundity after exposure to different species of bacteria. F. tularensis decreased male wing length in some treatments and significantly decreased fecundity in males and females. F. novicida had no significant effect on mosquito life history traits. L. pneumophila hastened development and decreased survival in some exposure times. P. aeruginosa increased wing lengths in exposed mosquitoes. In addition to life history assays, filtered water from bacterial biofilms was used to assay the effects bacterially secreted compounds have on oviposition choice in C. quinquefasciatus. In a basic choice test adult mosquitoes were given a choice of two oviposition substrates in four combinations (F. tularensis/mod hard water (MHW); F. novicida/MHW; P. aeruginosa/F. tularensis; P. aeruginosa/F. novicida). Ovipositing females preferred bacterially derived water to plain MHW and also preferred P. aeruginosa derived water to water derived from either Francisella species. The experimental system was effective in answering questions related to how mosquitoes and bacteria influence each other in the environment. Differing effects on mosquito development rate, survival, wing length, and fecundity were observed based on the species of bacteria to which mosquitoes were exposed, and pathogenic species were likely to have more effects on life history traits while non-pathogens had little effect on life history traits. Bacterial byproducts, in general, were attractive to ovipositing females in choice tests with biases toward P. aeruginosa over Francisella species. Future research will focus on answering questions related to how pathogenicity in humans could influence how a bacterial species influences life history traits in C. quinquefasciatus, and whether conditioning (due to being raised with a particular bacterial species) plays a role in preference for specific bacterial substrates for oviposition