Physiological host range of Trissolcus mitsukurii, a candidate biological control agent of Halyomorpha halys in Europe

The invasive stink bug Halyomorpha halys, native to East Asia, is a severe agricultural pest of worldwide importance, and chemical insecticides are largely sprayed for its control. Negative impact and failures of chemical pest management led to consider classical biological control as one of the most promising methods in a long-term perspective. The Asian egg parasitoid Trissolcus japonicus is the main candidate biocontrol agent of H. halys, but more recently a second species, Trissolcus mitsukurii, which shares the area of origin with H. halys, has drawn special attention after adventive populations were found in Europe. Despite its recent detection, intentional release or redistribution are bound to approval of national petitions, which requires detailed risk analyses. With the aim of providing a contribution for the future development of a risk assessment for release purposes, here we present the first study on the physiological (fundamental) host range of T. mitsukurii in Europe. Tests conducted on different hemipterans common to Southern Europe, using three different experimental designs, revealed a oligophagous host range, limited to Pentatomoidea and comparable with the host range displayed by T. japonicus under similar laboratory conditions. In addition to its coevolved host H. halys, T. mitsukurii successfully parasitized the majority of tested pentatomid species and one scutellerid, although with highly variable emergence rates. Notably high parasitization rates were detected on H. halys, Acrosternum heegeri and Dolycoris baccarum. Host egg sizes positively affected parasitoid size and female egg load. Although T. mitsukurii might be a promising biological control agent of H. halys in Europe, further studies (e.g., chemical ecology, field parasitism) are needed for assessment of non-target risks.