Bottom-Up and Top-Down Dynamics in the Management of Rosy Apple Aphid

Effective control of the rosy apple aphid, <i>Dysaphis plantaginea</i>, is crucial for maintaining apple orchard productivity. Understanding plant-mediated bottom-up and parasitoid-driven top-down interactions is critical for developing optimized pest management strategies. We investigated how host plant diversity and interactions between two parasitoids, <i>Aphidius matricariae</i> and <i>Aphidius ervi</i>, shape aphid suppression across seedlings from ten apple cultivars. Mummy counts, parasitism rate, emergence rate, and sex ratio measurements were used to assess the parasitoid preference and performance. Results revealed significant interactions between host plant identity and parasitoid performance. Mixed parasitoid releases outperformed single-species treatments. Alone, <i>A. ervi</i> achieved significantly higher parasitism rates than <i>A. matricariae</i>. Host plant effects were pronounced; Cripps Pink enhanced <i>A. matricariae</i> performance, while Golden Delicious and Red Delicious improved <i>A. ervi</i> metrics. Emergence rates and sex ratios varied by plant origins, with Elstar enhancing <i>A. ervi</i> and Granny Smith enhancing <i>A. matricariae</i>. Choice tests indicated cultivar-specific parasitoid preferences, and heatmap analysis revealed apparent competition among aphids mediated by parasitoids, with Braeburn and Gala acting as key parasitoid sources. Study findings indicate that managing apple cultivar diversity and exploiting complementary parasitoid interactions can improve <i>D. plantaginea</i> biocontrol in orchards.