Effect of carrier on the efficacy of Bacillus thuringiensis var. kurstaki (HD-1) formulations

Effect of carriers on the efficacy of powder formulations of Bacillus thuringiensis var. kurstaki (HD-1) is reported. Sixteen powder formulations were developed using eight carriers namely barium sulphate, bentonite, dolomite, Fuller's earth, kaoline, talc, precipitate of silica and pyrophyllite. Six physico-chemical properties namely bulk density, reaction (pH), cation exchange capacity, moisture content, sorptivity and specific surface area of the carriers were studied. Among the carriers tested, precipitate of silica was found to be the most suitable. LC₅₀ values of formulation-7 (0.018%) and formulation-15 (0.015%) employing precipitate of silica, showed them to be highly effective against 3^rd instar larvae of Helicoverpa armigera (Hübner).