Abstract: 【Aim】 This study aims to investigate the effect of wilforgine on muscular structure against adults of the oriental armyworm, Mythimna separata, so as to provide basis for further studying its insecticidal mechanisms. 【Methods】 M. separata adults were fed on acetone-sugar water solution of wilforgine to assay the toxicity and poisoning symptoms. The pathological changes in their muscular structure induced by wilforgine (300 μg/mL) were observed by light and electron microscope. 【Results】 Wilforgine had strong oral toxicity against M. separata adults with the LC₅₀ value of 194.53 μg/mL. The typical toxicity sign was paralysis leading to death. Microstructural examinations demonstrated that the muscular structure was damaged with increasing spaces between muscular fibers. The sarcolemma was digested and band structures disappeared. The ultrastructural examinations showed shed myolemma, swollen mitochondria and dilated sarcoplasmic in the muscle cells. Moreover, the damage to muscle cells increased with poisoning time. 【Conclusion】 Wilforgine could induce pathological changes in the flight muscle of M. separata adults, leading to death. Thus, the action site of wilforgine may be located in the muscle tissues of this insect.

Key words: Mythimna separata, wilforgine, toxicity, flight muscle, pathological change, action target