Abstract: The results obtained from leaf residue bioassays showed that the 3-instar and 5-instar larvae of the imported cabbage worm eating 4 kinds of vegetables,i.e.Chinese cale ( Brassica alboglabra Bailey),Pak-choi ( B. campestris L.),Flowering Chinese cabbage ( B. campestris L.) radish ( Raphanus sativus L.),had remarkably varied susceptibility to RH-5849, and the highest ratios of the LC 50 were 1.61 times for 3-instar larvae and 1.92 times 5-instar larvae. But after feeding on Flowering Chinese cabbage for a generation,the variation became less,and the highest ratios of the LC 50 were 1 22 times for 3-instar larvae and 1.15 times for 5-instar larvae respectively.