Will an accidentally introduced parasitoid save European box trees?

Abstract Introduction: An unidentified species of Eriborus (Hymenoptera: Ichneumonidae) is an important larval parasitoid of the box tree moth, Cydalima perspectalis (Lepidoptera: Crambidae) in its native range in South Korea. It is one of the parasitoid species being considered for classical biological control in Europe and North America, where C. perspectalis is a serious invasive pest of ornamental and wild box trees ( Buxus spp.). In spring 2024, an Eriborus sp. adult was caught in a botanical garden in Basel, Switzerland. To our knowledge, this was the first detection of this parasitoid in Europe. Methods: In spring 2025, surveys were made to assess parasitism of C. perspectalis populations at various sites in north-western Switzerland and at one site in south-western Germany. Results: These surveys showed that the parasitoid is well established in the region, both in gardens and in wild box tree stands. Morphological observations and molecular analyses showed that the specimens found in Switzerland and Germany belong to the same species as specimens collected on C. perspectalis in South Korea. Parasitism was highest in wild stands, reaching 68% in Germany and 32% in Switzerland. This parasitoid likely arrived unintentionally some years ago with the importation of box trees from East Asia. Conclusions: Cydalima perspectalis is seriously threatening the survival of European wild Buxus spp., and very few control options are presently available. The high parasitism rates observed at several sites in Switzerland and Germany provide hope for saving wild Buxus spp. stands from ecological extinction.