author(s)
Hareesh Shiralli, Basavaraj Kalmath, Prabhuraj A, Arunkumar Hosmani and Ayyanagouda Patil

abstract
Nineteen native Bacillus thuringiensis (Bt) strains isolated from soil samples were evaluated against II instar larvae of Spodoptera litura (Fab.) at College of Agriculture, Bheemarayanagudi, University of Agricultural Sciences, Raichur during 2018-19. The laboratory bioassays revealed that II instar S. litura larvae treated with 19 native Bt isolates showed mortality in range of 43.33 to 100% during preliminary screening. Highest mortality of 100% was recorded in HD-1 reference strain, which was on par with the native Bt isolates, BGC-1(96.66%), GBP-2(93.33%) and GHB-1(86.66%). Next best treatment was found to be Bt isolate BGC-2 which resulted in 83.33 per cent mortality. Lowest mortality (43.33 %) was recorded in Bt strain GHM-2 and no mortality was recorded in untreated control against II instar larvae of S. litura during preliminary screening. 89.47% of the Bt isolates (17/19) tested against II instar S. litura recorded more than 50% mortality. Median lethal concentration of the native isolates (BGC-1, GBP-2 and GHB-1) of Bt which recorded more than 85 per cent mortality in preliminary screening revealed that the toxicity of three potential B. thuringiensis isolates against second instar larvae of S. litura ranged from 2.89 to 21.31μg/ml. Among three potential isolates tested, isolate BGC-1 showed the least LC50 value of 5.24μg/ml and it was comparable to the reference strain HD1 with the LC50 value of 2.89μg/ml, this was followed by GBP-2 (8.65μg/ml) and GHB-1 (21.31μg/ml).