Abstract: After selection for resistance to butene-fipronil for 7 generations,the resistance ratio of the fourth instar larvae of diamondback moth,Plutella xylotella(L.)to butene-fipronil increased 77.58-folds.The susceptibility of butene-fipronil-resistant larvae to different insecticides were tested with topical application method.The results indicated that the butene-fipronil-resistant larvae showed no cross resisitance to abamectin,chlorpyrifos,methomyl,monosultap or beta-cypermethrin.The resistance ratio estimated to be 0.80~1.36-folds.The effects of butene-fipronil resistance on fitness of the diamondback moth were evaluated in terms of developmental and reproductive characteristics by constructing life table of resistance strain and susceptible strain.The results indicated that the resisitance strain had a fitness value of 0.84 relative to the susceptible one.Comparing with the susceptible strain,the resisitance strain possessed developmental disadvantages including prolonged larvae and pupa duration,decreased pupa body weight, ower pupation and emergence rate,as well as reproductive disadvantages including increased egg laying amount,lowered hatch ability and sex ratio (♀:♂),reduced life span and number of female adults.