Abstract: The biocontrol strain Isaria javanica MSC-F1 exhibits remarkable pathogenicity against Panonychus citri, showing a significant potential for further development for the management of P. citri. This study optimized the culture conditions and medium components of strain MSC-F1 using spore yield as an indicator through single-factor screening and multi-factor orthogonal tests to enhance the sporulation of the strain in liquid fermentation and to provide high-quality seed liquid for solid fermentation.. The findings revealed that the optimum culture conditions for the strain MSC-F1 were: temperature 29 ℃, rotation speed 200 r/min, inoculation volume 16%, liquid loading volume 50 mL/250 mL, culture duration 5 days, and pH level 6.0. The ideal medium consisted of glucose (45 g), soybean powder (15 g), and NaCl (0.50 g). The optimized fermentation process based on these parameters significantly increased sporulation yield by a factor of 5.8. The laboratory lethal tests demonstrated a positive correlation between the concentration of spore suspension and toxicity against P. citri. On the 8^th day post-inoculation, the LC₅₀ for adult P. citri was 1.69×10⁷ spores/mL and the LT₅₀ was 6.45 days at a spore concentration of 1.0×10⁸ spores/mL. In summary, the strain I. javanica MSC-F1 demonstrates an exceptional lethal activity against P. citri and can be significantly enhanced in sporulation yield through optimized fermentation processes, which lays a solid foundation for further industrial development of this biocontrol strain.

Key words: Isaria javanica, fermentation conditions, biocontrol, Panonychus citri, lethal effects