We investigated the species composition of egg parasitoids expected to be effective as a natural enemy of fruit-piercing stink bugs at north and south areas of Fukushima Prefecture, Japan from 2021 to 2023. Most of the egg parasitoids that emerged from sentinel frozen egg masses and field collected egg masses of Halyomorpha halys (Stål) at the north area in 2023 were of the genus Trissolcus. Similar trends were observed by the sweeping method, unaffected by the host type or condition on fruited cherry trees and mulberry trees, at both areas in 2021 and 2022. As a result, T. japonicus (Ashmead) was the dominant species at both survey areas and with the different survey methods. For hosts, Plautia stali Scott was the dominant species at the south area, while the proportion of H. halys tended to be slightly larger at the north area in this study. From the small ratio of other species that prefer P. stali, we conclude that T. japonicus is likely to function as a universally effective egg parasitoid of fruit-piercing stink bugs in these areas.
