Effect of Temperature of Extrinsic Incubation on the Vector Competence of Culex tarsalis for Western Equine Encephalomyelitis Virus *

Abstract

Culex tarsalis was a less competent vector of western equine encephalomyelitis (WEE) virus after 2–3 weeks' extrinsic incubation at 32°C than after incubation at 18° or 25°C. The high temperature itself was not directly detrimental to mosquito infection as all mosquitoes were initially infected, but subsequently some females were able to limit viral multiplication and/or dissemination. Elevated maintenance temperatures enhanced the expression of modulation, and elevated larval rearing temperatures selected for those females with this trait. This is the first report of an inverse relationship between temperature of extrinsic incubation within the range of 25°–32°C and vector competence of a mosquito for an arbovirus.