Ten species of mosquitoes became sensitive to CO2 following intrathoracic (i.t.) inoculation of California encephalitis (CE) virus. These included field-collected Aedes melanimon, Aedes nigromaculis and Culiseta incidens and laboratory-clonized strains of Aedes dorsalis, Aedes triseriatus, Anopheles freeborni, Culex peus, Culex pipiens pipiens, Culex pipiens quinquefasciatus and Culex tarsalis. Another California serogroup virus, Jerry Slough (=Jamestown Canyon) (JS), also induced CO2 sensitivity in nearly 100% of infected female Ae. dorsalis, Ae. melanimon and Cx. tarsalis. Sensitivity to CO2 developed in Ae. dorsalis and Cx. tarsalis within 3 days after i.t. inoculation of CE virus, remained at a high level through day 10 after inoculation and decreased gradually with time until by 30 days postinoculation nearly all mosquitoes were nonsensitive. In contrast, Ae. dorsalis infected transovarially with CE virus were not CO2 sensitive. There was homologous but no heterologous interference to the development of CO2 sensitivity when Ae. dorsalis infected transovarially with CE virus were inoculated with CE or JS viruses.
Two other bunyaviruses, Main Drain and Turlock, produced CO2 sensitivity in 3–10% and 0%, respectively, of infected Ae. dorsalis, Ae. melanimon and Cx. tarsalis. Two togaviruses, St. Louis encephalitis and western equine encephalomyelitis, did not induce CO2 sensitivity in Ae. dorsalis and Cx. tarsalis.
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