The invasive landscape pest Halyomorpha halys (Hemiptera: Pentatomidae) has been a problem in Michigan since it arrived in 2010 partly because few native natural enemies are able to attack it. An adventive population of an effective, coevolved parasitoid wasp, Trissolcus japonicus (Hymenoptera: Scelionidae) was found in Michigan in summer 2018 and a mass rearing had been initiated. Wasps reared in the lab were used to conduct augmentative releases at eight sites adjacent to apple orchards in summer 2019. At four of the sites 100 and at four different sites 900 adult T. japonicus were released. Four additional sites did not receive wasps and served as controls. Wasp establishment was monitored biweekly between June and Sept using H. halys sentinel egg masses. Potential non-target effects were monitored using native stink bug eggs (Podisus maculiventris). H. halys numbers were assessed with pyramid traps. No T. japonicus were captured in 2019 but four species of native parasitoids attacking H. halys were recovered from 4% of egg masses. We did not detect any non-target attack of T. japonicus on native stink bugs. At this point establishment of T. japonicus across Michigan cannot be confirmed but the lack of recapture can be due to dispersal and overall low densities across the state. Monitoring and further releases of T. japonicus will continue in 2020 to assess establishment and to increase the densities and distribution of this important biological control agent of H. halys in Michigan.

Additional Contributors: John Pote, Larry Gut, Julianna Wilson, and Marianna Szűcs