Preliminary Study on the Insecticidal Active Substances in the Roots of Gentiana macrophylla against Plutella xylostella

[Objective] The research aimed to study the insecticidal active substances in the roots of Gentiana macrophylla against Plutella xylostella.[Method] The active substances in the roots of G.macrophylla were extracted by ethanol ultrasonic method.The contact activity of the extracts against P.xylostella was tested by using insect-dipping method.The extracts were leached with petroleum ether,chloroform,ethyl acetate and n-butanol by using liquid-liquid allocation extraction method in order.The tracking test was made on the activity of each extract.[Result] LC50 of the extract from the roots of P.xylostella to the 3rd-instar larva was 0.795 8 g/ml.The activity of petroleum ether extract was strongest after separating the extracts,followed by chloroform extract and ethyl acetate extract.But the effects of n-butanol extract and remainder in water layer were not obvious.[Conclusion] The roots of G.macrophylla had stronger contact activity against P.xylostella and the insecticidal active substances were liposoluble compounds.