California encephalitis (CE) virus was transmitted transovarially by its natural vector, Aedes melanimon. Vertical transmission rates ranged from 13–26% in geographical populations of Ae. melanimon infected with CE virus by intrathoracic inoculation. No consistent pattern of transmission rates was detected for location or time of year mosquito collection. Vertical transmission rates ranged from 9–29% in Aedes dorsalis inoculated with CE viral strains isolated from Ae. melanimon collected in California. The month or year of viral isolation had no effect on the efficiency of vertical transmission. However, a viral strain isolated from the Owens Valley was less efficiently transmitted than strains from the Sacramento Valley, and strains from the San Joaquin Valley were intermediate in efficiency. Filial infection rates were highest in first ovarian cycle progency and declined with increasing ovarian cycles in both Ae. dorsalis and Ae. melanimon.
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