The Pilot Studies on the Screening and Bioactivity of Insecticidal Plants Against Pieris rapae(L)

The 95% ethanol extracts from 25 poisonous plant species were tested for the poison activity against 3rd instar larvae of Pieris rapae(L).The results showed that the extracts from Stellera chamaijasme L. and Croton tiglium L. had fairly good control effect. On that base, the author made gradient extraction from the anhydrous ethanol extracts of the two plants with three organic solvent including : n-hexane?chloroform and ethyl acetate. Through the insecticidal activity test of the extracts mentioned above, found out the n-hexane extract from Stellera chamaijasme and Croton tiglium had significant stronger poison activity and antifeedant activity against Pieris rapae. When diluted the test specimen at a concentration of 50 times dilution respectively, the death rates of the insects in 48h were 88.9% and 66.7%,in 72h reached as high as 95.6% and 91.1%, and the average antifeedant rates in 72h reached to 87.5% and 83.3%.