Abstract: This study evaluated the effects of combined application of Metarhizium rileyi Mr006 and chlorantraniliprole against Spodoptera frugiperda. Toxicity tests showed that, on the 7 th day after treatment with M. rileyi Mr006, LC₂₅, LC₅₀ and LC₉₀ against S. frugiperda were 8.97×10⁵ CFU/mL, 1.12×10⁷ CFU/mL and 1.37×10⁹ CFU/mL, respectively. For chlorantraniliprole treatment, the corresponding LC values on the 4 th day were 0.05 mg/L, 0.24 mg/L and 4.35 mg/L. Compatibility tests demonstrated that chlorantraniliprole at LC₂₅, LC₅₀ and LC₉₀ concentrations had no adverse effects on spore germination, mycelial growth or sporulation of M. rileyi Mr006. Regardless application sequence and interval time, all combined treatments significantly increased the corrected mortality of S. frugiperda, although the “fungus-first then insecticide” approach showed more pronounced synergistic effects than the reverse sequence. The highest corrected mortality reached 92.93% at 7 days post insecticide treatment following fungal treatment with a 36-hour interval. For mixing ratios, the 1:4 combination of M. rileyi Mr006 and chlorantraniliprole exhibited the most significant synergistic effect, achieving a 81.82% corrected mortality at 7 days post treatment. This study provides important theoretical basis and practical guidance for environmentally friendly control of S. frugiperda.

Key words: Metarhizium rileyi, chlorantraniliprole, Spodoptera frugiperda, toxicity, synergistic effect