Temperature alters Culex tarsalis West Nile virus vector competence, tissue bottlenecks, and transcriptional responses

West Nile virus is an arbovirus transmitted by Culex mosquitoes. Temperature is frequently the strongest abiotic factor impacting transmission in many virus-vector pairings, including WNV and Culex. However, it is unknown how temperature impacts WNV population bottlenecks and transcriptional responses to infection in Culex tarsalis. We found that elevated temperatures led to increased likelihood of transmission of rare virus variants due to increased vector competence and less stringent tissue barriers. Analysis of Cx. tarsalis transcriptional responses confirmed that WNV infection had minimal impacts on transcriptional activity. Temperature, however, induced significant changes to mosquito gene expression, whereas canonical immune gene expression minimally changed in response to infection. Thus, temperature impacts bottlenecks in the Culex-WNV system independent of known antiviral pathways, possibly by altering virus replication dynamics. While temperature had a dramatic impact on bottleneck stringency, this is likely independent of antiviral pathways and instead some other change to mosquito biology. Together, these results shed light on the relationships between temperature, virus evolutionary dynamics and antiviral immunity.