Potentiation of insecticidal activity of <i>Bacillus thuringiensis </i>subsp. <i>kurstaki </i>HD-1 by proteinase inhibitors in the American bollworm, <i>Helicoverpa armigera</i> (Hübner)

Abstract

The effect of crude proteinase inhibitor extracts from seeds of different crop plants (black gram, chickpea, chickling vetch, finger millet, French bean, green gram, horse gram, lentil, pea and soybean) on the insecticidal activity of <i>B.</i> <i>thuringiensis </i>var. <i>kurstaki </i>HD-1 was investigated against neonate larvae of <i>H. armigera </i>by diet incorporation method. The larval mortality due to crude proteinase inhibitors alone (5% seed weight equivalent) ranged from 4.1 to 19.1%; the maximum mortality with finger millet and the minimum with pea var. DDR-23. A mixture of <i>B. thuringiensis </i>var. <i>Kurstaki</i> HD-1 (10 ppm) and proteinase inhibitor (5% seed weight equivalent) was synergistic in larval mortality with respect to proteinase inhibitors of pea var. DMR-16, chickling vetch var. RLK-1098 and B101-212, lentil var. ILL-8095 and L-4076, soybean var. PK-1042, PK-416 and Pusa-22, chickpea var. Pusa-413, French bean (<i>Chitra</i>)<i> </i>and black gram; and antagonistic with respect to those of finger millet, horse gram and kidney bean. The larval growth reduction with crude proteinase inhibitors alone ranged from 17.9 to 53.1%; the maximum growth reduction with soybean var. PK-1042 and minimum with lentil var. L-4076. A mixture of <i>B. thuringiensis </i>var. <i>kurstaki </i>and proteinase inhibitor was synergistic in growth reduction with respect to proteinase inhibitors of lentil var. ILL-8095, and L-4626 and antagonistic with respect to that of finger millet.

The midgut proteinase inhibition with crude seed extracts (3.3% seed weight equivalent) ranged from 9.3 to 60.9% and was negatively correlated with larval mortality. These results showed that interactive effect of <i>B.thuringiensis </i>var. <i>kurstaki </i>HD-1 and proteinase inhibitors in the larvae of <i>H. armigera </i>depended upon the quality and quantity of proteinase inhibitors,

which vary widely in different plants.