Leaf surface structure shapes herbivore preference and predation efficiency: leaf-mediated biocontrol in a soybean system

Plant-herbivore-predator interactions shape community structure and ecosystem services (e.g., biocontrol). Herbivores often prefer the lower leaf side to avoid predators and environmental stress, but the mechanisms remain unclear due to confounding factors such as leaf orientation (upper vs. lower side) and surface structure (abaxial vs. adaxial surface). Here, we examined (1) herbivore preference for leaf orientation and surface structure (herbivory preference experiment), (2) its effect on predator–prey interactions (predation efficiency experiment), and (3) how leaf-mediated predation affects herbivore population dynamics and biocontrol (population growth modeling experiment). Using a soybean system consisting of soybean ( Glycine max ), soybean aphid ( Aphis glycines ), and six-spotted zigzag ladybeetle ( Cheilomenes sexmaculata ), we separated the effects of leaf orientation and surface structure with artificial leaves. We also experimentally reduced trichome density to evaluate its effect on predation rates and incorporated empirical data into population models. The results showed: (1) Aphid preference was primarily driven by leaf surface microstructure, particularly trichome density, rather than leaf orientation, with aphids favoring abaxial over adaxial surfaces (65.3% vs. 23.7%), consistent with higher trichome density on abaxial surfaces (8.46 vs. 2.35/mm 2 ). (2) Ladybeetle predation on aphids was 84.5% higher on adaxial surfaces, indicating that dense trichomes reduce predation rates. (3) Population growth models further showed that adaxial surface (sparse trichomes) enhanced aphid suppression by ladybeetles, highlighting the long-term influence of leaf-mediated predation on pest dynamics. Overall, this study demonstrates that plant structural traits mediate plant-herbivore-predator interactions and underscores the importance of integrating plant structure into crop breeding and pest management.