2008 Volume 12 Issue 1 Pages 27-33
West Nile virus (WNV) became established in New York in 1999, in the first outbreak in the Western Hemisphere. WNV is propagated in many species of birds and has been detected in more than 300 bird species in the United States, although there are great differences in the viremia level among the various bird species. Culex mosquitoes, including Cx. restuans, the Cx. pipiens complex and Cx. tarsalis are important vectors of WNV in the USA. Laboratory transmission of WNV by Cx. pipiens form molestus showed that they were highly competent vectors of WNV, with infection and dissemination rates of 96% and 81%, respectively. Three species, including two of the Culex pipiens group (Cx. pipiens pallens (as pallens in this article) and Cx. pipiens form molestus (as molestus in this article)) and Aedes albopictus, account for more than 99% of collected mosquitoes surrounding Tokyo. The Cx. pipiens complex (pallens, molestus and Cx. quinquefasciatus) prefer both human and avian hosts, and there is no clear differences in avian blood-feeding patterns between pallens and molestus, but there are significant differences among mammalian species, with molestus preferring human blood compared with pallens. Ducks (mallards & spotbill ducks) and tree sparrows are major blood sources for the Cx. pipiens group in Japan, which are moderate or high amplifiers of WNV. From a larval bioassay with several kinds of insecticides it was demonstrated that etofenprox, a synthetic pyrethroid, exhibited relatively low effectiveness against several mosquito colonies of the Cx. pipiens group in an urban environment of Japan. The most important larval habitats of the Cx. pipiens group and Ae. albopictus are catch basins along public roads and this kind of structure should be targeted to control mosquito larvae.
