Abstract: In laboratory experiments,several bioassay methods were used to evaluate the activities of buprofezin against brown planthopper(BPH,Nilaparvata lugens)nymphs.Results showed that the contact effect is the major mode of action of buprofezin.Although it also possesses systemic action,this has no practical impo tince in field control.Buprofezin showed no effects on the nymphs confined to the rice leaf sheathes when only the leaves were treated with buprofezin.In field exper.ments,buprofezin showed much higher efficacy in controlling both the BPH and the whitebacked planthopper(WBPH,Sogatella furcifera)than the conventional insecticides MIPC and methamidaphos.The number of planthoppers was suppressed to a very low level within a long period of more than 1 month after treatment by 37.5-75g(AI)/ha.of buprofezin,Field experiments also indicated that buprofezin had little detrimental effects on spicers which are important natural enemies of planthoppers.