Bacillus thuringiensis (Bt) gram positive entomopathogenic bacteria being an eco-friendly biopesticide. In present study the potential of B. thuringiensis isolates was studied for the biological control of Diamond back moth (DBM). Fifteen Bt isolates were obtained from the Department of Agricultural Microbiology, TNAU Tamil Nadu. This mainly isolated from the cultivated lands Cotton (Gossypium hirsutum), Brinjal (Solanum melongena) and Tomato (Solanum lycopersicum). All the 15 isolates were

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... tified as B. thuringiensis based on the crystalline structure. Four different types of crystalline forms were observed, in which the isolates CC, CB1, BC, TD, BD were produces cuboidal shape crystals. Then, the isolates were characterized based on presence of lepidopteron specific cry gene. Among the 15 B. thuringiensis isolates seven of them were found to be positive for lepidopteron specific cry genes include cry 1 & cry 2. Four Bt isolates were exhibited presences of both cry 1 and cry 2 genes. The selected 4 isolates further screened for protein profiling by SDS Page. Molecular weights of the protein ranging from 65 to 130 kDa. Toxicity of this four B. thuringiensis isolates were evaluated by bioassay using third instar larvae of the diamondback moth (Plutella xylostella) and isolate (CC) recorded maximum mortality of 95.33% comparable to standard strain HD1 98.31%. In quantitative bioassay, the LC50 for third instar larvae of Plutella xylostella was found to be least range 197.09 ppm with fiducial limits of 110.28 - 352.21 ppm respectively. Different concentration of the toxic protein (100, 250, 500, 750, 1000, 2000) will reduce the leaf damage and larval growth was (54-8% and 58-25%) observed. This achieved effective control of DBM in cauliflower plant.