Biological Control

Introduction of Trissolcus japonicus for the control of Halyomorpha halys

Classical biological control, with the release of antagonists native to the pest’s area of origin, has been claimed as the most suitable approach to restore control of H. halys once it has been introduced into newly invaded areas. Trissolcus japonicus, also known as micro-samurai wasp, has been identified as the most promising biocontrol agent, considering both its specificity and high parasitization rate. Adventive populations of T. japonicus have been recorded in Europe since 2017.

Italy is the first country in which a program has been implemented with all the key features of biocontrol initiatives: importing T. japonicus into quarantine facilities to assess the parasitoid's range; obtaining approval for release from the relevant authorities (the Ministries of Agriculture and Environment and the Istituto Superiore di Sanità); experimental rearing of the biocontrol agent; and inoculating individuals in the new area so that they can independently increase in response to the host populations.

Activities and results:

The Province of Bolzano has adhered to the three-year release program for T. japonicus since 2020, continuing in 2023. Releases occurred three times each season at more than 40 sites located in the main valleys of the province. In 2023, releases occurred at only 10 sites. During the four-year experimental period, constant monitoring was conducted to assess the reproductive capacity, spread and effectiveness of T. japonicus against the marmorated stink bug. Particular attention was paid to adverse effects on non-target organisms, especially the possible parasitization of T. japonicus on native pentatomids. Parasitization of T. japonicus against H. halys has increased over the years starting from 34.1% in 2020 to 65.7% in 2023. T. japonicus has represented the main parasitoid of H. halys since 2021. At local scale, overwintering and establishment capacities were assessed in pre-release and at selected locations outside the release sites. The long-term monitoring showed that the parasitoid is able to overwinter and settle in different areas.