Characterization of modulation of western equine encephalomyelitis virus by Culex tarsalis (Diptera: Culicidae) maintained at 32 degrees C following parenteral infection.

Two lines of Culex tarsalis Coquillett genetically selected for low or high western equine encephalomyelitis (WEE) virus production (low viral producer [LVP] or high viral producer [HVP], respectively) modulated WEE (i.e., decreased the concentration of virus to < 10(4) plaque-forming units after intrathoracic inoculation). The LVP line modulated WEE more than HVP, and modulation was most pronounced at 32 degrees C. At 15 degrees C, viral replication to high titers occurred in both lines. When infected LVP were transferred to 15 degrees C after 4 d extrinsic incubation at 32 degrees C, replication of WEE to high titers did not occur. Mosquitoes transferred from 15 degrees C after replication to high titers occurred; to 32 degrees C did significantly modulate WEE titer. Incubation at 32 degrees C prior to infection had no effect on the degree or timing of WEE modulation in both LVP and HVP lines. Most LVP infected following feeding on a high dose of WEE had salivary gland infection barriers. Viral modulation by Cx. tarsalis was an alphavirus phenomenon, and was not restricted to WEE.