Abstract: Alkaloid is the main insecticidal composition in Tripterygium wilfordii Hook f., a famous insecticidal plant. In order to study its insecticidal action and judge its prospects, we assayed the effects of total alkaloid on the growth, development and six metabolic enzymes of the 5th instar larvae of Mythimna separate (Walker). The results showed that the treated larvae had marked reduction in body weight, weight gain and relative growth rate compared with the control. The growth rate, survival rate and pupation rate of the treated M. separata larvae and the emergence rate of the treated adults were lower than those of the control. Esterase and carboxyl esterase (CarE) in the treated  insects were distinctly activated. The activities of acid phosphatase (ACP) and alkaline phosphatase (ALP) in the treated insects were remarkably inhibited by total alkaloid all the time except ALP activity at 3 h after treatment. The activity of glutathione S-transferases (GSTs)  was distinctly activated by total alkaloid at 3, 12 and 24 h after treatment, and was equal to that of the control at 36 h and 48 h after treatment, but was inhibited at 48 h after treatment. The O-demethylase activity of cytochrome P450 (MFO) showed no distinct change at 3 h after treatment and then was activated at 12 and 24 h after treatment, but was not different from the control at 36 h and 48 h after treatment.

Key words: Tripterygium wilfordii, total alkaloid, Mythimna separata, growth and development, metabolic enzymes