Mortality effect of BT extracts and esterase variability in three stored grain insects: Callosobruchus chinensis, Sitophilus granarius and Tribolium castaneum

Bioassay was conducted to determine the susceptibility level of the adults of Callosobruchus chinensis, Sitophilus granarius and Tribolium casteneum against four BT isolates (1i, 27s, 27f and HD73) where mortality effects were counted from 24 to 192 hours (8 days) at 24 hours of intervals. All strains of BT were highly active against C. chinensis and the LC50 were found to be 0.30, 0.73, 0.62 and 0.22 mg/ml against 1i, 27s, 27f and HD73 respectively, while, the LC90 were found to be 0.72, 2.02, 1.24 and 0.74 mg/ml, at 72 hours of exposure. Considering the LC50 and LC90 values, HD73 was found to be the most effective strain. Contrary to C. chinensis, mortality was found to be very low against S. granarius and T. castaneum and was not subjected for statistical analysis. The adult of all three insects were subjected to 7.5% polyacrylamide gel electrophoresis (PAGE) and altogether four esterase bands (Est-1 3.87 , Est-2 1.62 , Est-3 0.96 and Est-4 0.52 ) were found in C. chinensis and S. granarius, while three bands (Est-1 3.87 , Est-3 0.96 and Est-4 0.52 ) were observed in T. castaneum with variation in staining intensity. When treated with malathion or cypermethrin, esterases were inhibited by insecticides and faintly stained bands were observed in the treated dead samples of all three species as compared with non treated control. © 2012 Universal Research Publications. All rights reserved