Abstract: Bioassays of the methanol extract of Daphne tangutica, a local endemic plant in QinghaiTebet Plateau, for insecticidal effects on the imported cabbage worm, Pieris rapae, were carried out. The results showed that the extract possessed high effects of antifeedant and stomach poison. Fraction 9 of Silica gel column chromatography proved to be the most active fraction among those partitioned from the methanol extract by bioassaydriven separation. The larvae fed on leaf discs treated with fraction 9 grew slowly, and their bodies were smaller than those of the control. Histological study indicated that the tissue of midgut was destroyed and fatbody became to fade out by autolysis. The preliminary physiological reaction studies showed that fraction 9 could reduce the content of protein in haemolymph and inhibited the activity of esterase in midgut significantly.

Key words: Daphne tangutica, Pieris rapae, bioactivity, physiological reaction