Community structure of predators in walnut orchards and biocontrol effectiveness of the dominant species, Hippodamia variegata (Coleoptera: Coccinellidae) on the small walnut aphid, Chromaphis juglandicola (Hemiptera: Aphididae) in southern Xinjiang.

Infestations of the small walnut aphid, Chromaphis juglandicola (Kalt.), seriously threatens the yield and quality of walnut in southern Xinjiang, China. Understanding the dominant natural enemies of pests in the crop is crucial for optimizing conservation strategies to enhance ecological services. Through field surveys, this study revealed that ladybugs and lacewings had the highest dominance and temporal niche breadth indices among predatory insects. The temporal niche overlap index between ladybugs (predominantly Hippodamia variegata (Goeze)), and C. juglandicola was the highest, with their population peaks strongly coinciding. In cage experiments with H. variegata under varying predator/aphid ratios (1 : 50, 1 : 100, 1 : 150, 1 : 200, 0), we found that a predator-to-prey ratio exceeding 1:100 effectively suppressed C. juglandicola population growth, achieving over 70% biocontrol efficacy within 1 wk. Furthermore, in the field, the growth rate of C. juglandicola was significantly and negatively correlated with the ratio of ladybugs to aphids. Path analysis indicated that for every unit increase in the predator-to-aphid ratio, biocontrol efficacy improved by 63.4% (the standardized effect coefficient in path analysis), and the aphid population growth rate decreased by 65.2%. This study confirmed that H. variegata is the dominant predator of C. juglandicola in walnut orchards of southern Xinjiang. A predator/aphid ratio exceeding 1:100 effectively suppressed aphid population growth, maintaining it at low levels. These findings provided critical theoretical support for developing biological control strategies using H. variegata to manage C. juglandicola in walnut orchards of southern Xinjiang.