Abstract: 7-Demethoxytylophorine is an alkaloid isolated from insecticidal plant Cynanchum komarovii. In this study,the stomach toxicity of 7-demethoxytylophorine on 3th instar larvae of Plutella xylostella L.was tested with a leaf dipping method.The possible mechanism of action was examined based on the analysis of the effects of 7-demethoxytylophorine on the digestive enzyme and midgut tissues of P.xylostella. The results indicated that 7-demethoxytylophorine had a significant toxicity on P.xylostella. At the concentration of 8.00 mg/mL, the mortality rate was 76.67%.Meanwhile,an obvious damage in the poisoned larval’s midgut was observed.The activity of amylase,proteinase and lipase was significantly inhibited by 71.60%,93.38% and 89.20% after 48 h of treatment.The results suggested that the stomach toxicity of 7-demethoxytylophorine against P.xylostella might be related to its damage on the midgut tissues and the inhibition in the digestive enzyme activity of P.xylostella larve.

Key words: 7-demethoxytylophorine, Plutella xylostella L., stomach toxicity, digestive enzymes, midgut tissue