Abstract
In order to determine the origin of the parasitoid, Torymus (Syntomaspis) sinensis native to Tsushima Islands, parasitoids of the chestnut gall wasp were investigated at several localities in South Korea, from where the parasitoid might have come flying accidently into Tsushima. As a result, the parasitoid was proved to occur throughout South Korea including Cheju Island. It was, however, concluded that the parasitoid populations of Tsushima and Korea were different from a Chinese population in the seasonal prevalence of adult emergence, and that the Tsushima population belonged to the same ecotype as that of the southern part of South Korea. Therefore, the Tsushima population either originated in southern Korea or was native to Tsushima where it originally occurred as a parasitoid of an unknown native cynipid host on a oak tree.
