First discovery of adventive populations of Trissolcus japonicus in Europe

The brown marmorated stink bug, Halyomorpha halys (Stål), native to East Asia, emerged as an invasive pest in Europe in the 2000s. In its native range, Trissolcus japonicus (Ashmead) is the dominant egg parasitoid of H. halys, and thus it has been considered for classical biological control in countries invaded by the pest. A survey of native egg parasitoids conducted in 2017 and 2018 with frozen, sentinel egg masses of H. halys revealed that T. japonicus was already present in apple orchards in the Canton Ticino, Switzerland. Trissolcus japonicus was recovered in both years and from three different sites. In total, 17 egg masses were recovered from which 42 adult parasitoids emerged. A genetic analysis using the barcode mitochondrial DNA confirmed the morphological identification of T. japonicus and evidenced a best match of the “Ticino populations” to Japanese populations, but the pathways of entry remain unknown.