ST-LOUIS-ENCEPHALITIS VIRUS TRANSMISSION FOLLOWING MULTIPLE FEEDING OF CULEX-PIPIENS-PIPIENS (DIPTERA, CULICIDAE) DURING A SINGLE GONOTROPHIC CYCLE

Some mosquitoes may feed on a viremic host and ingest a small quantity of blood insufficient for initiating maturation of the oocytes, yet containing enough virus to infect the mosquito. After an appropriate extrinsic incubation period, such a mosquito could then become a potential vector while remaining nulliparous. Under experimental conditions, 3 of 31 (9.7%) Culex pipiens pipiens became infected with St. Louis encephalitis (SLE) virus after partial engorgement and without becoming gravid. In addition, SLE virus was transmitted from bird to bird by 2 Cx. p. pipiens during a single gonotrophic cycle. Multiple feeding during a single gonotrophic cycle could increase the chances of mosquitoes acquiring and transmitting virus. Also, if an infective partial blood meal taken in late summer or autumn were followed by successful hibernation, winter carryover of virus could be accomplished by nulliparous mosquitoes.