Studies On Bacillus Thuringiensis Strains WY-190 And WY-197 With High Toxicity Against Spodoptera Exigua

Two Bacillus thuringiensis strains with high toxicity against Spodoptera exigua, WY-190 and WY-197, were obtained by bioassay screening from 100 wild-type strains. The 50% lethal concentration values (LCsos) of final whole culture of the WY-190 were 0.25, 0.43 and 1.29 ml culture per milliliter diet (ml/ml) against neonate, second-, and third-instar larvae of S.exigu, respectively; and that of the WY-197, 0.31, 0.61 and 2.57ml/ml, respectively. It also showed WY-190 and WY-197 were 8- and 7-times more toxic than HD-1 against neonate of S.exigua, respectively. The data exhibited the toxicity of WY-190 was higher than that of WY-197, especially against third-instar larvae of S.exigua although both of them had outstanding high toxicity against S.exigua larvae younger than third instar. By bioassays against neonate of Helicoverpa armigera at 26癈 ?1, the WY-190, WY-197 and HD-1 fermented broth were proved to have the potency of 686, 3000 and 3750IU/U L, respectively. The neonate of H. armigera was more sensitive to the fermented broth of WY-197than that of WY-190.In addition, the study discussed the morphological, physiological and biochemical properties and crystal proteins of WY-190 and WY-197. The serological identification indicated WY-190 and WY-197 were Hs^b serotype (B.thuringiensis subsp. Kurstaki); the SDS-PAGE displayed that the crystal proteins produced by the two strains were mainly composed of 135- and 65kDa proteins. The WY-190 strain was found that it could produce chitinase during its growth by further observed. The different bipyramidal in size, small cuboidal, elliptic and mosaic crystals, which were obtained from WY-190 strain alongside the sporangium during sporulation, could be observed in transmission electron microscope.