Abstract
A recent increase in phytophagous stink bugs in South Tyrol prompted an extensive two-year study across 27 sites aimed to explore the distribution and abundance of stink bug species and their egg parasitoids. Monitoring sites were located across the region in apple orchards, forest margins and urban areas within three altitude ranges, from 200 to 1000 m a.s.l. The developmental stages of collected stink bugs were recorded and associated to the host plant. Findings revealed significant species variations across habitats and altitudes, with forests and urban areas hosting richer diversity and higher abundance compared to apple orchards. The invasive brown marmorated stink bug, Halyomorpha halys (Stål), was the main species found up to 800 m. Its presence was concentrated in urban areas, but it represented the most abundant species also in orchards. The forest bug, Pentatoma rufipes (Linnaeus), was the predominant species above 800 m and in forest areas. In fact, this species could be found on several plant species of the families Betulaceae and Fagaceae, where other stink bug species were usually not present. Plant species of the families Cornaceae and Oleaceae were mostly visited by H. halys and the green shieldbug, Palomena prasina (Linnaeus). These plant families include species that are commonly present also in orchard hedgerows. Stink bugs were most commonly found among plant species within the Acer genus, which is widely chosen for ornamental landscaping in urban environments, but it also includes species used in ecological infrastructures of orchards. Most egg masses of different stink bug species were also collected on these plants. Additionally, plant species in the families Rosaceae, Oleaceae and Betulaceae hosted a high number of egg masses. On average, one third of the collected eggs was parasitized. Parasitization varied among sites, according to stink bug species and habitat type. For instance, egg masses of native species such as P. prasina and P. rufipes showed high parasitization percentages in both urban and woodland areas, while egg masses of the invasive H. halys were mainly parasitized in urban areas. Presence and impact of parasitoids were greater on host plants with greater stink bug presence. Additionally, in urban areas as well as in apple orchards more specialized parasitoids, belonging to the genera Trissolcus and Telenomus were found, while the generalist Anastatus bifasciatus (Geoffroy) was the main species emerging from egg masses collected in forest habitats. These results give insights into the complex ecological dynamics of stink bugs, their host plants, and associated parasitoids in the region, and could be useful in improving biological control strategies for stink bugs in the agroecosystem.