Population dynamics and interactions between true bugs and their egg parasitoids, both indigenous and exotic, in agroforestry systems

The increasing importance of invasive and native stink bugs (Hemiptera: Pentatomidae, Acanthosomatidae and Coreidae) in agricultural systems has highlighted the need for sustainable management strategies based on a deeper understanding of their ecology and interactions with natural enemies. This PhD thesis investigated the population dynamics of true bugs and their egg parasitoids in the Alpine agroforestry landscape of South Tyrol (Northern Italy), with particular emphasis on the invasive brown marmorated stink bug, Halyomorpha halys, and on the role of biological control. Field surveys conducted over two years across an altitudinal gradient and different habitat types (apple orchards, forests and urban areas) revealed that habitat and elevation strongly influence stink bug and parasitoid communities. Urban environments hosted the highest abundances of H. halys, whereas native species such as Pentatoma rufipes and Palomena prasina were more closely associated with forest habitats and higher elevations. A rich parasitoid complex was documented, including both native species and the exotic parasitoid Trissolcus japonicus, which is currently used in classical biological control programmes against H. halys. Native stink bugs generally showed higher parasitism levels than the invasive species, indicating more established host-parasitoid relationships. A second research component focused on the seasonal use of host plants by H. halys, P. prasina and P. rufipes. Monitoring conducted on 85 plant species demonstrated clear differences in host plant preferences and phenology among the three species. Sapindaceae, especially Acer spp., represented key resources for reproduction and development, while temporal variation in host plant use strongly influenced parasitoid occurrence and parasitism dynamics. The results highlighted the importance of these interactions in shaping multitrophic relationships within agricultural landscapes. To explore conservation biological control strategies, laboratory experiments evaluated the suitability of sixteen flowering plant species as nutritional resources for three important egg parasitoids: Anastatus bifasciatus, Trissolcus japonicus and Trissolcus mitsukurii. Several species, including buckwheat (Fagopyrum esculentum), dill (Anethum graveolens), mallow (Malva sylvestris) and brown knapweed (Centaurea jacea), significantly improved parasitoid longevity and, in some cases, parasitism performance. Both commercially available and locally sourced plant species provided valuable resources, suggesting opportunities for integrating regional flora into habitat management programmes. Finally, a two-year field experiment assessed the effectiveness of flower strips in organic apple orchards. Although flower strips successfully enhanced floral resource availability and attracted diverse arthropod communities, their effects on parasitoid activity and egg parasitism were variable and highly dependent on local environmental conditions. These findings indicate that habitat enhancement alone may not consistently increase biological control services and should be considered within a broader landscape context. Overall, this thesis demonstrates that interactions among stink bugs, host plants and egg parasitoids are shaped by habitat composition, elevation, seasonal resource availability and management practices. The results provide new ecological insights and contribute to the development of sustainable pest management strategies that reduce reliance on chemical control while promoting biodiversity and ecosystem services in Alpine agroecosystems.