Vertical transmission of St. Louis encephalitis (SLE) virus to F1 larval progeny was demonstrated in 8 species of mosquitoes which occur in Florida: Culex quinquefasciatus, Cx. nigripalpus, Cx. salinarius, Cx. restuans, Cx. opisthopus, Anopheles quadrimaculatus, An. albimanus, and Aedes taeniorhynchus. Relatively high rates of such transmission were observed in Ae. taeniorhynchus and vertical transmission to F1 adult progeny and venereal transmission from males to females also were demonstrated with this species. Larval rearing temperature affected transstadial transmission of the virus in Ae. taeniorhynchus, especially to the adult stage. Such transmission was observed with a larval rearing temperature of 18°C but not at 27°C. Because of the abundance and distribution of Ae. taeniorhynchus in Florida, and the relatively high rates of vertical transmission of SLE virus observed in the present experiments, this mosquito species warrants further investigation as a possible overwintering host for the virus in that locality.