First record of Trissolcus japonicus (Ashmead) (Hymenoptera, Scelionidae) in western Slovenia: Evidence from a multi-year survey of stink bug egg parasitoids

The global invasion of the brown marmorated stink bug (BMSB), Halyomorpha halys (Stål) (Hemiptera: Pentatomidae), is responsible for high economic losses to agriculture worldwide. As classical biological control is considered the most effective long-term management approach, an intensified research activity has been carried out worldwide aimed at discovering the most effective natural enemies of BMSB. In western Slovenia, monitoring for the presence of stink bug egg parasitoids has been ongoing since 2019. The results from a five-year survey (2021–2025) indicate overall egg parasitism rate ranging from 8.5% to 33.8% over the study period, with an average of 19.6%. The native Anastatus bifasciatus (Geofrey) (Hymenoptera: Eupelmidae) was the most abundant and widespread parasitoid of BMSB in the region. It accounted for 47% of all parasitoids in the complex and parasitized 9.2% of the host’s eggs. It was followed by non-native Trissolcus mitsukurii (Ashmead) (Hymenoptera: Scelionidae) which represented 31% of the parasitoid complex and contributed 6.1% to the overall egg parasitism rate. Trissolcus japonicus (Ashmead) (Hymenoptera: Scelionidae) ranked third (21%) despite being recorded only in the final two years of the study, with contribution 4% to total egg parasitism rate. BMSB eggs were also parasitized in low numbers by Trissolcus basalis (Wollaston) and Trissolcus cultratus (Mayr) (Hymenoptera: Scelionidae). The first detection of T. japonicus in Slovenia in 2024, and its subsequent records in 2025, confirm its establishment in the country and represent an important milestone that may facilitate the future implementation of classical biological control of BMSB.