Adventive Population of Trissolcus japonicus (Hymenoptera: Scelionidae), Parasitoid of Halyomorpha halys (Hemiptera: Pentatomidae), Discovered in Southwestern Idaho

Adventive populations of Trissolcus japonicus (Ashmead) have been detected in the eastern and western United States including the western states of Washington, Oregon, California, and Utah. These populations may provide classical biological control for the invasive brown marmorated stink bug, Halyomorpha halys (Stål), which can cause economic loss to many specialty crops in western North America. Idaho has not previously been surveyed for the exotic T. japonicus or native parasitoids of H. halys. In July 2021, T. japonicus was discovered emerging from wild H. halys egg masses in Star, Idaho (43.69788, −116.49427), and was detected on yellow sticky cards from July to September. This is the first record of T. japonicus in the state of Idaho. T. japonicus constituted only a small portion of Trissolcus species detected; other species included T. euschisti (Ashmead), T. hullensis (Harrington), and T. utahensis (Ashmead). Genetic population level analysis of T. japonicus specimens from Idaho supports the likelihood of its expansion inland from the west coast, inhabiting ecozones previously considered unsuitable due to high temperatures and low humidity. This report opens the prospect of an effective biological control agent for H. halys in Idaho and potentially other hot and dry geographic regions and expands documentation of the presence of adventive T. japonicus populations in North America.