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. Keywords Biological control • Egg parasitoids • Halyomorpha halys • Scelionidae Key message • Surveys for egg parasitoids of Halyomorpha halys were conducted in southeastern Switzerland. • For the first time, the Asian parasitoid T. japonicus was recovered from sentinel H. halys egg masses in Europe. • Trissolcus japonicus is established in Switzerland and was found in two consecutive years at three different sites. • Parasitism levels by T. japonicus are currently low, with a maximum of 2%. Communicated by D.C. Weber.

The brown marmorated stink bug Halyomorpha halys 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 H. halys. Adventive populations of two candidates for releases, Trissolcus japonicus and Trissolcus mitsukurii, 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 Tr. japonicus and Tr. mitsukurii. Within four years after their first detection in Europe, both species have rapidly spread into all types of habitats where H. halys is present, showing a wide distribution and continuous expansion. Both exotic Trissolcus showed high levels of parasitism rate towards H. halys, while parasitization of non-target species was a rare event. The generalist Anastatus bifasciatus was the predominant native parasitoid of H. halys, while the emergence of native scelionids from H. halys eggs was rarely observed. The presence of the hyperparasitoid Acroclisoides sinicus was also recorded. This study provided fundamental data that supported the development of the first inoculative release program of Tr. japonicus in Europe.

The reduction of atmospheric sulphur dioxide pollution is causing increasing problems of sulphur deficiency in sulphur-demanding crop plants in northern Europe. Elemental sulphur and many sulphur containing compounds such as cysteine-rich antifungal proteins, glucosinolates (GSL) and phytoalexins play important roles in plant disease resistance. The aim of this work was to analyse the effect of inadequate sulphur supply on disease resistance of oilseed rape (Brassica napus). Compared with fertilized oilseed rape, healthy looking S-deficient plants showed increased susceptibility to the blackleg fungus Leptosphaeria maculans, to the generalist necrotroph Botrytis cinerea and to the oomycete Phytophthora brassicae. To analyse possible causes of the increased disease susceptibility of S-deficient plants, protein extracts and methanolic extracts of secondary metabolites of plants grown with and without adequate sulphur supply were tested for antimicrobial activity. None of the protein extracts showed antimicrobial activity. However, extracts containing secondary metabolites from normally grown plants showed a strong antimicrobial activity in in vitro tests with various fungal and bacterial pathogens. This activity was almost totally lost in extracts derived from S-deficient plants. The antimicrobial activity did not appear to be based on the activity of phytoalexins because it was present in healthy plants and was not increased by a previous inoculation with Botrytis cinerea. The loss of antifungal activity in S-deficient plants correlated with a strong reduction of various GSL, thus suggesting a reduced level of GSL as a possible cause of the reduced antimicrobial potential. However, limited tests of commercially available GSL or their degradation products did not demonstrate a causal link. Our results show that S-deficiency of oilseed rape negatively affects disease resistance and suggest that this effect is at least partially caused by a reduction of sulphur-dependent phytoanticipins.

The generalist egg parasitoid Anastatus bifasciatus (Geoffroy) (Hymenoptera: Eupelmidae) is the most prevalent egg parasitoid of the invasive Halyomorpha halys (Stål) (Hemiptera: Pentatomidae) in Europe. To assess its efficacy against the pest H. halys and to validate the potential risks for non-target species in a realistic field setting, inundative releases were conducted over three consecutive years in four fruit orchards in Switzerland and Italy. In total, more than 4300 A. bifasciatus females were released, which was equivalent to 11,000 to 26,000 females per hectare, depending on distances between trees in each orchard. Parasitism of freeze-killed sentinel H. halys eggs achieved with the current release strategy was on average 6% (range: 2%–16%) and considered not high enough to effectively suppress the pest. However, the overall impact of A. bifasciatus on the mortality of H. halys eggs was likely underestimated. If pre-imaginal parasitoid mortality (3.3%) and host feeding (6%) are added to the observed parasitism (6%), the actual induced mortality of H. halys eggs may reach more than 15%. Parasitism of lepidopteran non-target species reached an average of 8% and thus, some degree of non-target parasitism after mass releases may be expected. To quantify the impact of the parasitoids in the orchards more precisely, naturally laid egg masses should be used in future trials to include host-finding cues of the host and host plants, and larger scale releases with potentially higher densities of parasitoids should be considered.

Summary. Oilseed rape, Brassica napus L. (cv Express), plants were grown under three different sulphur regimes: sulphur-free (S 0 ), normal sulphur (S n , normal field concentration) and a sulphur-rich (S + , 2 × concentration of S n ). We performed dual choice oviposition assays with the diamondback moth, Plutella xylostella, using real plants and, for the first time with this insect, artificial leaves sprayed with methanolic leaf-surface extracts. The results mirrored those of a separate study of preferences for whole plants. Females laid more eggs on surrogate leaves that were treated with S n extracts than on S 0 plants, while only a slight, not significant, difference was observed between extracts of normal and sulphur-rich plants. This shows that chemical compounds on the leaf surface mediate the oviposition preference and that the female insect can perceive the quality of the host-plants in terms of their fertilisation status.Since leaf volatiles are known to be oviposition stimulants, we investigated the effects of leaf-surface extracts on insect olfactory responses using electroantennograms (EAGs). In agreement with the behavioural data, we found that extracts of sulphur-treated plants yielded higher EAG amplitudes than the S 0 extracts. Since the leaf content of the volatiles isothiocyanates is influenced by sulphur nutrition, we analysed the extracts for these compounds. Above the detection threshold of our GC-MS system, no isothiocyanates were found. Thus, other compounds present in the surface extracts must be perceived by the antenna.However, the HPLC analysis revealed 11 different glucosinolates. Progoitrin (2-Hydroxy-3-butenyl) and gluconapoleiferin (2-Hydroxy-4-pentenyl), which belong to the hydroxy-alkene class of glucosinolates, were the most abundant compounds. The total glucosinolate content sharply increased from S 0 to S n plants, whereas it was slightly lower in S n versus S + plants. Since it is known that glucosinolates can stimulate oviposition, it seems likely that the increased content we observed was influencing the insect preference in this study too.