Abstract
Two species of Aedes (Stegomyia) were collected in response to the first chikungunya virus (CHIKV) outbreak on Yap Island: the native species Ae. hensilli Farner and the introduced species Ae. aegypti (L.). Fourteen CHIKV-positive mosquito pools were detected. Six pools were composed of female Ae. hensilli, six pools were composed of female Ae. aegypti, one pool was composed of male Ae. hensilli, and one pool contained female specimens identified as Ae. (Stg.) spp. Infection rates were not significantly different between female Ae. hensilli and Ae. aegypti. The occurrence of human cases in all areas of Yap Island and the greater number of sites that yielded virus from Ae. hensilli combined with the ubiquitous distribution of this species incriminate Ae. hensilli as the most important vector of CHIKV during the outbreak. Phylogenic analysis shows that virus strains on Yap are members of the Asia lineage and closely related to strains currently circulating in the Caribbean.