Toxicity of Total Alkaloid from Tripterygium wilfordii Hook against Mythimna separata(Walker)and Its Effects of on AChE and Ach

Alkaloid is the main insecticidal composition in Tripterygium wilfordii Hook,a famous insecticidal plant.In order to study its insecticidal activites and mechanism,the stomach toxicity of the total alkaloid against larvae of Mythimna separata Walker was tested,their toxicity symptoms were observed,and its effects on the activities of AChE and the content of ACh of larval heads in different toxicity stages were assayed.The results showed the stomach toxicity LD50 values of the total alkaloid against the 3rd instar larvae of M.separata in 24,48,96 and 120 h post treatment were 306.39,216.12,157.18 and 129.92 mg/L.In vivo toxicity symptoms were characterized by a definite sequence of events,starting with moving slowly,stopping feeding,flaccid paralysis and recovering or death.Anabiotic insects started feeding,were paralyzed,recovered or died again and up to death.It was presumed the total alkaloid from T.wilfordii influenced the nerve system of insects.AChE was not strongly inhibited or activated by the total alkaloid.ACh content in paralysis stage wasn′t significantly different with that of the control and lower in recovery stage.