The main objective of our research was to investigate the biology and seasonal dynamics of the brown marbled stink bug (Halyomorpha halys [Stål]) in Westeren Slovenia, driven by biotic and abiotic factors. Over the period 2019-2021 the biological parameters of the species were studied in the semi-field experiment at Kromberk (Nova Gorica). During the same period, we followed the seasonal population dynamics of H. halys in three apple orchards (Malus domestica [Suckow] Borkh.) in the Goriška region using Pherocon® Dual Panel Adhesive Traps (Trece Inc.) and pyramidal Rescue® Stink Bug Traps, both baited with Trécé lures. Furthermore, a two-year field survey of native stink bug egg parasitoids was conducted. In Goriška region, H. halys developed two overlapping generations/year with high net reproductive rates for 3 consecutive years. The migration of H. halys adults from overwintering shelters started at the end of March. The first-generation adults emerged in mid-July, and the second-generation adults in mid-September. Nymphs occurred from mid-June to the end of October. Pyramidal traps were more effective than clear sticky traps; they caught notably more both adults and nymphs. Halyomorpha halys adult trap captures were higher in the Šempeter orchard, within the area of great landscape diversity and a large share of urban land. The seasonal dynamics of H. halys was closely related to weather conditions, with temperature and relative humidity as the major factors affecting population growth. Four native egg-parasitoid species Anastatus bifasciatus (Geoffroy), Telenomus sp., Trissolcus basalis (Wollaston) and Ooencyrtus telenomicida (Vassiliev, 1904) were found in the wider area of the Goriška region, and one non-native species Trissolcus mitsukurii (Ashmead). All of them were able to parasitize H. halys eggs and all of them are new records for Slovenia. Overall parasitism rates of naturally laid eggs by the parasitoid species complex in 2019 and 2020 were 3.0 and 14.4 %, respectively.
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