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Unintentional introduction of natural enemies has increased in recent years due to a massive rise in global trade and tourism. One such natural enemy is the Asian egg parasitoid Trissolcus japonicus, a promising agent for classical biological control of Halyomorpha halys. In Europe, adventive T. japonicus populations have been detected in Switzerland, Italy and Germany. Host specificity testing demonstrated that its fundamental host range is fairly broad; however, it is unclear whether spatial or temporal refuges reduce parasitism of non-target species in the field. To address this, the realized host range of T. japonicus was assessed over three years by exposing sentinel egg masses of H. halys and 18 non-target species and collecting naturally laid egg masses in Switzerland and Italy. In total, 15 of 18 non-target species were successfully parasitized by T. japonicus in the field, confirming its broad fundamental host range. However, most non-target species were less parasitized by T. japonicus than H. halys, profiting from either partial temporal or spatial refuges from parasitism. Species with an unusual life cycle and the same ecological niche as H. halys, such as Pentatoma rufipes, which was the most parasitized non-target species in both countries, potentially face an increased risk of parasitism. In contrast, beneficial non-target effects may occur for the invasive pest, Nezara viridula, which suffered high non-reproductive mortality induced by T. japonicus. In both cases, life table studies will be needed to determine the impact of non-target parasitism and the potential consequences at the population level. [ABSTRACT FROM AUTHOR]

The brown marmorated stink bug, Halyomorpha halys, native to East Asia, is an invasive alien pest that arrived in Europe in the early 2000s and poses an imminent threat to a wide variety of crops. Adventive populations of the Asian egg parasitoid Trissolcus japonicus, the most promising agent for classical biological control of H. halys, have recently been detected in Italy and Switzerland. Its prospective fundamental host range in Europe was evaluated in behavioural no-choice tests, followed by large-arena choice tests presenting host plants with naturally laid egg masses of target and non-target hosts. Developmental suitability of European non-target host species for T. japonicus was demonstrated, via no-choice tests, by offspring emergence (successful parasitism) from eleven out of thirteen non-target species tested (85%). Whereas successful parasitism of most non-target species was significantly lower, acceptance of Arma custos, Palomena prasina, Pentatoma rufipes, and Rhaphigaster nebulosa was not significantly different from H. halys controls. When eggs of H. halys and non-target species were exposed in a semi-natural situation in large-arena choice tests, the degree of non-target parasitism was substantially reduced for three out of four tested species, whereas parasitism of Pa. prasina eggs was not. It remains unclear if there are behavioural barriers to parasitism that may exist and preclude excessive parasitism of potentially threatened species in the field, but field data from the invaded areas in Switzerland and Italy could contribute to a risk–benefit evaluation of releasing or re-locating adventive T. japonicus populations into other parts of Europe. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]