Temporal effect on insecticidal activity of Bacillus thuringiensis Berliner Var. kurstaki, strain ABTS-351, against Corcyra cephalonica

Bacillus thuringiensis (Bt) formulations are the most successful biopesticides now regularly used in many IPM programs against lepidopteran pests. Newer formulations like DiPel contain strain ABTS-351 as active toxin product, which is essentially an isolate of HD-1. Insecticidal activity assay of Dipel DF was performed to characterize the strain for its insecticidal efficacy against Rice moth, Corcyra cephalonica larvae; and the effects of duration of exposure. The obtained mortality curves for the three exposure durations were typically sigmoid as expected. Longer duration of exposure increased the mortality. Lethal concentration values, obtained through Probit analysis for 24, 48 and 72 hrs exposure against log concentration of Bt, yielded LC50 value (with 95% confidence limits) of Bt on C. cephalonica 4th instar larvae as 65.813 (52.946 – 85.689), 36.311 (29.953 – 45.704) and 17.745 (15.350 – 20.742) mg/mL respectively. The insecticidal activity was found to be comparatively much efficient at lower concentrations with longer exposures. This feature is the potential key to a more efficient biocontrol strategy, allowing other compatible biocontrol agents to be combined for a far more effective, or even synergistically, control over pest.