A 3-year survey on parasitism of Halyomorpha halys by egg parasitoids in northern Italy

A 3-year survey was carried out to assess the impact of egg parasitoids on Halyomorpha halys in northern Italy. In total, 1826 H. halys egg masses were collected in the 3 years, and parasitoid adults emerged from 12% of eggs in 2016 and 2017, and from 21% in 2018. Anastatus bifasciatus was the main species emerging from H. halys eggs at all sites and years, confirming its ability to develop on fresh H. halys eggs. Only a few adults of native scelionid species emerged: Trissolcus kozlovi (first record in Italy), T. semistriatus, T. basalis and Telenomus turesis. In addition, a few adults of the Nearctic hyperparasitoid Acroclisoides solus (first record in Europe) were obtained from H. halys eggs collected at different sites. In 2018, for the first time an adventive population of Trissolcus japonicus was also recorded at one site, where the parasitism rate by the parasitoid species complex was overall higher than in 2016 and 2017. An additional supplemental survey at other sites of northern Italy in 2018 revealed the presence of T. japonicus and Trissolcus mitsukurii. The distribution and abundance of T. japonicus, T. mitsukurii and A. solus should be further investigated. Their host range and their interaction with native egg parasitoids, especially with A. bifasciatus, should be also assessed to better understand their potential role in biological control of H. halys.