Abstract: To develop environment-friendly control resources for the soybean aphid, Aphis glycines, a pathogenic bacterial strain, designated XP-1, was isolated from diseased aphids. It was subsequently identified and evaluated for its potential for biological control. The isolate was identified based on morphological observation, physiological and biochemical characteristics, and molecular biology. The leaf-dipping method was used to determine its virulence against adult soybean aphids, and TWOSEX-MSChart was employed to assess its effects on aphid development and reproduction. The strain XP-1 was identified as Serratia marcescens. A 6-day exposure of aphids to the bacterial suspensions (1×10⁶ to 1×10¹¹ cfu/mL) resulted in corrected cumulative mortality ranging from 17.89 % to 58.95 %. The median lethal concentration (LC₅₀) was 6.62×10⁹ cfu/mL. At a concentration of 1×10¹¹ cfu/mL, the median lethal time (LT₅₀) was 4.49 days. Furthermore, exposure to the bacterial suspensions significantly disturbed the developmental duration of F1 generation nymphs, shortened adult longevity, reduced fecundity, and decreased body size, and led to a significant decrease in population net reproductive rate (R₀), intrinsic rate of increase (r), and finite rate of increase (λ). In conclusion, Strain XP-1 demonstrates direct toxicity and remarkable transgenerational sublethal effects, showcasing its great potential as a sustainable agent for biological control of the soybean aphid.

Key words: soybean aphid, Serratia marcescens, biological control, virulence, sublethal effect