First detection of Trissolcus japonicus (Ashmead) (Hymenoptera, Scelionidae) in southwestern France

We report the first detection of Trissolcus japonicus in southwestern France. A total of almost 3000 sentinel and 700 field-laid egg masses of Halyomorpha halys were exposed or collected in the administrative region of Nouvelle-Aquitaine in 2022 and 2023. A total of 12 and 44 specimens of T. japonicus emerged from one and two egg masses in 2022 and 2023, respectively. Morphologic analysis confirmed the identification of this egg parasitoid, while molecular analysis of COI matched the haplotype of the French population to the population of T. japonicus released in Italy. Trissolcus japonicus may have arrived in Nouvelle-Aquitaine from introduction pathways similary to T. mitsukurii, detected in 2020, although these pathways cannot be clearly defined. The co-occurrence of these two major parasitoids of BMSB should now be surveyed as possible competition can arise. In the frame of the biological control program currently running in France against BMSB, the use of one or two parasitoid species is also considered.