Genetic variation of sweet potato weevils, Cylas formicarius(Fabricius)(Coleoptera: Brentidae), in main infested areas in the world based upon the internal transcribed spacer-1(ITS-1)region

Genetic variations of the internal transcribed spacer-1 region in sweet potato weevil, Cylas formicarius, were examined from 27 collection sites in the main infested areas in the world, except Africa, in this study. The ITS-1 lengths of 36 weevils tested in this study ranged from 557 to 587 bp, and were conspicuously longer in weevils from India. The genetic distances between weevils from India and from the other areas tested were larger than among weevils from the latter areas. The phylogenetic tree based on ITS-1 sequences consisted of two main clades of India and East Asia consisting of Northeast Asia and Southeast Asia subclades. The former subclade was also divided into three minor subclades. Weevils from Georgia and Hawaii (USA), and St. Kitts (the West Indies) belonged to the same subclade as those from Guangdong (China) and Hanoi (Vietnam). Also, weevils from the Ogasawara Islands (Japan) belonged to the same subclade. On the other hand, weevils from the Southwest Islands (Japan) belonged to the same subclade as those from Taiwan. When referring to human historical events, C. formicarius would have gradually spread in southern Asia due to its limited dispersal ability since originating in the Indian subcontinent 90 million years ago. However, after becoming associated with sweet potato, especially after the nineteenth century, local populations with fairly different genetic properties from Indian weevils would have been rapidly spread by human transportation of infested sweet potato throughout the world.