Abstract
This study reports the results of a 2016–2017 survey on the distribution of the sweet potato weevil, Cylas formicarius (Fabricius), across all seven inhabited islands in the Tokara Islands, southern Japan. The weevil was found on all surveyed islands, mainly utilizing wild Convolvulaceae plants as hosts due to the lack of sweet potato fields. Clear differences in the occurrence status of C. formicarius were observed among the seven islands, depending on the distribution of wild host plants. The weevil was commonly found on Suwanosejima, Kodakarajima, and Takarajima islands, where wild host plants were abundant. In contrast, it was only slightly present on Kuchinoshima, Nakanoshima, Tairajima, and Akusekijima islands, where wild host plants were rare, primarily due to feeding damage by feral goat. These findings suggest that Suwanosejima, Kodakarajima, and Takarajima islands pose a relatively high risk of serving as the invasion source, as the weevil could be unintentionally transported by a regular passenger and cargo ferry. Therefore, to mitigate the risk of its spread into mainland Kyushu from the Tokara Islands, it is necessary to eliminate wild host plants growing in and around ferry ports, particularly on the three islands.
