Vector competence of Ochlerotatus trivittatus (Coquillett), Aedes albopictus (Skuse), and Culex pipiens (L) (Diptera: Culicidae) for West Nile virus
Kenneth B. Platt
West Nile virus (WNV) was recognized in North America in 1999. Avian species are the primary reservoir of the virus and can develop viremias with titers higher than 1010.0 CID50s/ml. Culex species of mosquitoes are the primary amplifying vectors. Many species of mammals are also susceptible to WNV but develop viremias that seldom exceed 105.0 CID50s/ml. Mammals may play a significant role in WNV ecology if mosquitoes that feed on them during periods of viremia can be infected and transmit the virus. The primary objective of this study was to determine vector competency of Ochlerotatus trivittatus (Coq.) a potential bridge vector that feeds primarily on mammals including humans and occasionally on birds. Susceptibility of Oc. trivittatus to WNV was compared to that of Aedes albopictus (Skuse) a known bridge vector, and Culex pipiens (L.), a primary amplifying vector by determining infection rates after feeding mosquitoes on chicks with blood meal titers (BMTs) of 102.5 to 1010.0 CID50s/ml. The ability of Oc. trivittatus to transmit WNV was determined by comparing transmission rates (%) of Oc. trivittatus, Ae. albopictus and Cx. pipiens by the capillary tube method following infection by blood meals with titers ranging from 102.5 to 109.5 CID50s/ml. Susceptibility of Oc. trivittatus and Cx. pipiens to WNV was essentially the same but greater than Ae. albopictus. The lowest infective BMTs for Oc. trivittatus, Ae. albopictus and Cx. pipiens were 104.5 , 105.5, and 104.5 CID50s/ml. The 50% infective BMTs for the 3 species were 106.0 10 6.6, and 106.2 CID50s/ml. Transmission rates of Oc. trivittatus, Ae. albopictus, and Cx. pipiens after blood meals with titers higher than 107.0 CID 50s/ml were 41.7, 72.4 and 46.8%. The lowest BMTs that resulted in transmission by the 3 species were 105.5, 107.0, and 10 5.5 CID50s/ml. These observations suggest that Oc. trivittatus might play a more significant role than Ae. albopictus in maintaining WNV in populations of mammals which typically develop low levels of viremia.