Assessing the Distribution of Exotic Egg Parasitoids of Halyomorpha halys in Europe with a Large-Scale Monitoring Program

The brown marmorated stink bug is an invasive agricultural pest with a worldwide distribution. Classical biological control has been identified as the most promising method to reduce the populations of . Adventive populations of two candidates for releases, and , have recently been detected in Europe. To assess their distribution and abundance, a large-scale survey was performed. From May to September 2019, a wide area covering northern Italy and parts of Switzerland was surveyed, highlighting the expanding distribution of both and Within four years after their first detection in Europe, both species have rapidly spread into all types of habitats where is present, showing a wide distribution and continuous expansion. Both exotic showed high levels of parasitism rate towards , while parasitization of non-target species was a rare event. The generalist was the predominant native parasitoid of , while the emergence of native scelionids from eggs was rarely observed. The presence of the hyperparasitoid was also recorded. This study provided fundamental data that supported the development of the first inoculative release program of in Europe.