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In 1966 and 1967, from a freshwater swamp in northwest Hillsborough County, Florida, 165,354 mosquitoes were collected in CDC light traps supplemented with Dry Ice. Virus isolation was attempted from species pools of all collections. There were 128 isolations of the California group arboviruses Keystone and trivittatus: 99 from Aedes atlanticus, 28 from Aedes infirmatus, and 1 from Anopheles crucians. Keystone virus was most abundant (119 isolations) and was found most often in A. atlanticus; 8 of 9 isolations of trivittatus virus were from A. infirmatus. In both years, isolation of virus was made from the first generation of Aedes that appeared after the first heavy spring rain. The largest number of isolations was made in August, when peak densities of these mosquitoes occurred. Oviparity rates and minimum infection rates of both species appeared to be related; precipitin tests indicated that they fed mainly on wild mammals. The higher rates of feeding of A. atlanticus on rodents may be significant in view of the consistently higher infection rate in this species and the recent isolation of Keystone virus from two wild-caught cotton rats (Sigmodon hispidus). Moreover, a marked increase in the infection rate with California group viruses of A. atlanticus in 1967 over 1966 corresponds with a doubled rate of feeding on rodents. No evidence of transovarian transmission of virus was found in nulliparous mosquitoes of both species.
Present address: Hillsborough County Arthropod Control Unit, P. O. Box 1731, Tampa, Florida 33601.
Present address: Epidemiology Research Center, Florida Division of Health, 4001 Tampa Bay Blvd., Tampa, Florida 33614.
Present address: Entomological Research Center, Florida Division of Health, P.O. Box 308, Vero Beach, Florida 32960.