Characteristics of Bacillus thuringiensis strain YX-1 with high toxicity to Lepidopteran apple pests

A strain of Bacillus thuringiensis (Bt) strain,YX-1,with high toxicity to apple tree pests was isolated from soil in Hebei.In order to explore the feasibility of using this to control apple pests the toxicity of Bt YX-1 to some apple tree pests was assayed.The crystal shape,protein type,genotype and growth characteristics of Bt YX-1 were also observed and analyzed.A light microscope indicated that Bt XY-1 has crystals with a bipyramidal shape.SDS-PAGE analysis indicates that this strain produced 130 ku and 60 ku protein bands.PCR-RFLP analysis revealed the presence of cry1Ac,cry2Ac,cry1I,vip3Aa and cry34-35 genes.The bioassay results show that Bt YX-1 was highly toxic to larvae of Hlyphantria cunea,Helicoverpa armigera,Prodenia litura,Grapholitha molesta,Adoxophyes orana and Phalera flavescens with respective LC50 of 14.48 mg/L,2.72×103 mg/L,6.24×104 mg/L,1.01×102mg/L,3.52×104 mg/L and 4.73×103 mg/L.The toxicity of Bt YX-1 was higher than that of Bt HD-1.Although supernatant from a culture broth of Bt YX-1 showed very low insecticidal activity (8.33% mortality) against 2nd instar larvae of H.armigera it markedly improved the toxicity of a mixture of spores and crystals.Our results show that the Bt YX-1 may prove valuable as a microbial control agent for lepidopteran pests or apple crops.