Longevity and spontaneous flight activity of Culex tarsalis (Diptera : Culicidae) infected with western equine encephalomyelitis virus

The longevity of an Iowa strain of Culex tarsalis Coquillett fed blood meal s containing 2 concentrations of western equine encephalomyelitis virus fro m Iowa (WEE-7738) was compared with that of Cx. tarsalis fed blood without virus. Females exposed to 4.7-5.0 log TCID50 per mosquito of WEE-7738 did n ot live as long as mosquitoes exposed to 2.7-3.0 log TCID50 per mosquito or controls. Only 1% of mosquitoes fed blood containing the higher virus conc entration survived to day 18 after exposure. However, 13% of mosquitoes fed blood with the lower virus titer and 19.5% of the controls were still aliv e on day 18 after exposure. Flight activity scores of Cx. tarsalis infected with 4.7-5.0 log TCID50 per mosquito of WEE-7738 were 27.5% lower, and the re were 26.1% fewer spontaneous nights than noninfected controls from days 6-11 after infection. After day 8 after infection, infected Cx. tarsalis ha d 37.1% lower activity scores and 40.0% fewer spontaneous nights than nonin fected controls. Virus infection did not affect how long a mosquito new in a 24-h period (the daily flying time) or the duration of individual nights. The spontaneous night activity pattern (circadian rhythm) of infected mosq uitoes was identical to those of controls. Both infected and noninfected mo squitoes began spontaneous flight activity at 2000-2100 hours (CST) and wer e active throughout the entire dark phase of the 24-h cycle. Although mosqu itoes were active throughout the night, there was a burst or peak of activi ty between 2200 and 2300 hours when the complete dark cycle began. These re sults indicate that the adverse effect of WEE infection on longevity and sp ontaneous night activity of Cx. tarsalis may decrease vectorial capacity of Cx. tarsalis for WEE.