In vitro evaluation of native Bacillus thuringiensis isolates against II instar Spodoptera litura (Fabricius)

The larval mortality was found to be increased significantly with increase in concentration among all the Bt strains tested. The probit analysis results with second instar larvae of Spodoptera litura showed LC₅₀ value that ranged between 0.10 x 10^-1 to 0.10 x 10^-7 CFU/1ml. The reference strain HD1 showed the least LC₅₀ value of 0.10 x 10^-1 CFU/1ml with fiducial limits ranging from 0.63 x 10^-11 to 0.10 x 10^-4 CFU/1ml. Among all the native Bt strains tested strain 375 exhibited least LC₅₀ value of 0.10 x 10^-6 CFU/1ml with fiducial limits ranging from 0.31 x 10^-9 to 0.10 x 10^-4. CFU/1ml. Least LC₉₀ value 0.35 CFU/1ml was recorded for HD1 (fiducial limits 0.63 x 10^-1 to 0.13 x 10² CFU/1ml) followed by Bt strain 375 with LC₉₀ value 0.01 x 10² CFU/1ml (fiducial limits 0.25 x 10² to 0.11 x 10³).