What's for Dinner?: A genetic analysis of host preference variation in Culex pipiens mosquitoes

Abstract

Mosquitoes have the capacity to carry diseases and infect humans worldwide. Biting preferences of such vectors can play a large part in predicting if host populations could fall prey to these insects. One species of mosquito called Culex pipiens includes two forms of the insect: form pipiens and form molestus. One of the main physiological differences between the two forms is that pipiens favors avian bloodmeals, while molestus prefers mammalian bloodmeals. Hybridization between the two forms produces an admixed Culex population feeding on both birds and humans, possibly leading to an increase in West Nile Virus (WNV) transmission from birds to humans. This hybridization event provides an opportunity for a genetic analysis of the host preference variation seen in these mosquitoes. Utilizing Philadelphia, Pennsylvania as a trapping site, we collected mosquitoes in traps baited with either bird odor or mammal odor. We found that mosquitoes in the area were more responsive to the bird odor. We then looked for genetic polymorphisms associated with host preference by sequencing pools of mosquitoes that responded to either type of odor. From these pools, 233 single nucleotide polymorphisms (SNPs) were found to be both differentiated between all bird vs. mammal pools and undifferentiated between bird pools and between mammal pools. These SNPs were located in 35 genes across the Culex quinquefasciatus genome. Three genes were found to be associated with olfaction and host-seeking behavior. One of these genes encodes the mRNA for Odorant Receptor 94B. This finding provides further evidence that odor is a significant influence that contributes to the differential host preferences seen in the Philadelphia Culex pipiens population. Future studies will provide more information about the function of these specific genes and their direct relation to host-seeking behaviors, elucidating how Culex pipiens came to specialize on humans as a host.