Abstract: In this paper, the toxicities of seven quinolizidine alkaloids from Sophora alopecuroids against turnip aphids and their effects on several esterases were studied. The results showed that one of the alkaloids cytisine is highly effective against the insect than anabasine and nicotine which are famous aphidcides. The median lethal concentrations of the alkaloids against the apterous aphid are 432.59, 684.70 and 1 090.65 mg/L respectively, 48 h after treatment by dipping method. By means of colorimetry the activities of some esterases treated with the alkaloids were studied. The results indicated that the alkaloids could inhibit activity of acetylcholinesterases (ACHE), the effectiveness of inhibiting AChE is: total alkaloids from the plant＞cytisine＞sophoraminesophoradine＞sophocarpine＞oxymatrine＞matrine＞aloperine. Cytisine and aloperine inhibit the activity of a-NA esterase, a-NA carboxylesterase and esterase isozyme as well.

Key words: Sophora alopecuroids, quinolizidine alkaloid, turnip aphid, toxicity, es- terase