2014 Volume 58 Issue 3 Pages 237-247
The West Indian sweet potato weevil, Euscepes postfasciatus Fairmaire, was distributed only on Nansei and Ogasawara (Bonin) Islands in Japan until 2008, when the weevil was found for the first time in Ibusuki City, which previously regarded as a weevil-free area. In this study, we used epidemiological approaches to determine how the weevil population in Ibusuki City was established. We conducted spatial distribution analysis and case–control studies based on survey data gathered from 270 farmers who cultivated sweet potato in 2008. Weevils were present at 46 sweet potato (Ipomoea batatas) cultivation sites and four blue morning glory (Ipomoea indica) growing sites. The weevil infestation rate was higher in sweet potato plants than in wild host plants. Weevil infestation was strongly associated with the use of tuber trench silo storage (odds ratio, 4.45). The association with silo storage suggested that the tuber storage silos provided an overwintering refuge for the weevil. The case–control study also revealed that cultivation without pesticides and for home use were associated with weevil infestation. Activities such as the transfer of tubers or leaving tubers in the field may expand the distribution of the weevil population over a wider area.
