[Objective] The aim of the study was to explore the resistance development of deltamethrin through selection of deltamethrin resistant strain of wild silkworm(Bombyx Mandarina),thus providing the basis for scientific pesticide application and resistance management.[Method] The wild silkworms collected from three different regions were reared indoors,and the sensitivity of their parents to deltamethrin was detected by topical application.The larvae in each generation were treated with deltamethrin in median lethal dose or so by topical application.The mortality of larva was analyzed for the establishment of toxicity regression equations and the calculation of the multiple or increased multiple of deltamethrin resistance.[Result] After the Qidong Bombyx Mandarina(YQD) fed with mulberry leaves were selected for three generations indoors,the multiple of deltamethrin resistance of F4 was 14.26,1.2 times as great as that of F0;after the Bombyx Mandarina from mulberry garden of Soochow University(YSD) fed with mulberry leaves were selected for three generations indoors,the multiple of deltamethrin resistance of F4 was 16.48,1.9 times as great as that of F0;after the Wujiang Bombyx Mandarina(YWJ) fed with artificial diets were selected for three generations indoors during six generations,the multiple of deltamethrin resistance of F6 was 18.67,1.2 times as great as that of F0.[Conclusion] With the selection in same dose,the resistance multiple of YSD increases more rapidly than that of YQD;under double selection of artificial diets and insecticide,the resistance multiple of YWJ increases more slowly than that of YQD. [Objective] The aim of the study was to explore the resistance development of deltamethrin through selection of deltamethrin resistant strain of wild silkworm (Bombyx Mandarina), thus providing the basis for scientific pesticide application and resistance management. [Method] The wild silkworms collected from three different regions were reared indoors, and the sensitivity of their parents to deltamethrin was detected by topical application. larvae in each generation were treated with deltamethrin in median lethal dose or so by topical application. mortality of larva was analyzed for the establishment of toxicity regression equations and the calculation of the multiple or increased multiple of deltamethrin resistance. [Result] After the Qidong Bombyx Mandarina (YQD) fed with mulberry leaves were selected for three generations indoors, the multiple of deltamethrin resistance of F4 was 14.26, as great as that of F0; after the Bombyx Mandarina from mulberry garden of Soochow Univer sity (YSD) fed with mulberry leaves were selected for three generations indoors, the multiple of deltamethrin resistance of F4 was 16.48,1.9 times as great as that of F0; after the Wujiang Bombyx Mandarina (YWJ) fed with artificial diets were selected for three With indoors during six generations, the multiple of deltamethrin resistance of F6 was 18.67, 1.2 times as great as that of F0. [Conclusion] With the selection in same dose, the resistance multiple of YSD increases more rapidly than that of YQD; under double selection of artificial diets and insecticide, the resistance multiple of YWJ increases more slowly than that of YQD.