ECOLOGY OF MOSQUITOS AND LACK OF ARBOVIRUS ACTIVITY AT MORRO BAY, SAN-LUIS OBISPO COUNTY, CALIFORNIA

During 1994-95, totals of 17,656 adult females and 111,104 adults rear ed from field-collected immatures comprising 19 species in 4 genera of mosquitoes were collected from Morro Bay estuary and surrounding envi rons in San Luis Obispo County, California. Aedes dorsalis was the dom inant summer mosquito, whereas Aedes squamiger and Ae. washinoi were a bundant during winter and early spring. Host-seeking Culex tarsalis we re collected infrequently, even though immatures were collected freque ntly from freshwater surface pools. Overall, 13,561 adults (386 pools) and 91,547 adults reared from field-collected immatures (3,027 pools) were tested for arboviruses by plaque assay in Vero cell culture. Mor ro Bay virus, a member of the California serogroup, was isolated from 4 pools of Ae. squamiger reared from field-collected immatures (minimu m field infection rate = 1.07 per 1,000), verifying the maintenance of this virus by vertical transmission. All remaining pools were negativ e. Three hocks of 10 sentinel chickens and one group of 5 sentinel rab bits were bled biweekly and tested for arbovirus antibodies with negat ive results. Neither horizontal nor vertical transmission of western e quine encephalomyelitis virus was detected.