Enhancing Biological Control of Maize Seedling-Stage Pests Through Combined Application of Cnidium monnieri and Endophytes

Agricultural intensification has weakened natural pest regulation by reducing habitat resources for natural enemies and limiting plant-mediated resistance. Here, we conducted field experiments during 2024–2025 to evaluate the combined effects of Cnidium monnieri field-margin planting and maize seeds coated with the endophytic fungal strains YC (Beauveria bassiana) and PL (Purpureocillium lilacinum) on predator conservation, pest suppression, and biological control in maize agroecosystems. Compared with natural grass margins, C. monnieri significantly increased predator abundance, species richness, and Shannon diversity, particularly of ladybirds, minute pirate bugs, and spiders (p < 0.05). Gut-content analysis detected C. monnieri DNA in ladybirds collected 10–40 m from field margins, confirming predator resource use and spillover into maize fields. Importantly, endophytic fungus-coated seeds did not reduce predator abundance or diversity. Moreover, combining C. monnieri with endophytic fungi enhanced pest suppression and achieved control efficacy comparable to imidacloprid (p > 0.05). These findings demonstrate that integrating functional plants with endophytic fungi simultaneously strengthens top-down biological control and endophyte-associated bottom-up pest suppression, providing an effective and environmentally sustainable strategy for pest management in maize.