Bacteria-mediated regulation of Aphidius gifuensis parasitism efficacy in Myzus persicae: Implications for biological control strategies

Abstract Aphidius gifuensis, a key parasitoid of Myzus persicae in tobacco agroecosystems, has been extensively implemented in Chinese biological control programs for over a decade. This sustained augmentation strategy has not only established stable field populations of A. gifuensis but also significantly suppressed aphid densities and associated viral disease transmission. However, long-term laboratory maintenance of both aphid hosts and parasitoid colonies has resulted in diminished biological fitness of A. gifuensis, manifesting as reduced parasitic efficacy and elevated control costs. To address these challenges in mass rearing and field application, our investigation focused on: (1) Identification of endosymbiotic bacteria within M. persicae and A. gifuensis, and (2) Evaluation of bacterial influences on aphid reproductive biology. Key findings include:1. Microbial characterization: Seven bacterial endosymbionts spanning five genera were isolated. Lysinibacillus fusiformis was uniquely associated with aphids, while Bacillus cereus and Stenotrophomonas maltophilia were specific to parasitoids. Four additional parasitoid-associated species were identified: Bacillus pumilus, Bacillus subtilis, Acinetobacter radioresistens, and Exiguobacterium sibiricum.2. Reproductive modulation: All isolates demonstrated significant effects (p < 0.01) on aphid fecundity. S. maltophilia exhibited the strongest oviposition stimulation (88.38% increase vs. control), contrasting with A. radioresistens showing maximal suppression (47.13% reduction).3. Physiological impacts: A. radioresistens significantly upregulated aphid phenoloxidase (1.64% increase) and superoxide dismutase (SOD) activity (2.99% elevation). Notably, this bacterial strain induced differential regulation of stress-response proteins compared to controls.