Negative Effects of a Nonhost Proteinase Inhibitor of ~19.8 kDa from Madhuca indica Seeds on Developmental Physiology of Helicoverpa armigera (Hübner)

An affinity purified trypsin inhibitor from the seed flour extracts of Madhuca indica (MiTI) on denaturing polyacrylamide gel electrophoresis showed that MiTI consisted of a single polypeptide chain with molecular mass of ~19.8 kDa. MiTI inhibited the total proteolytic and trypsin-like activities of the midgut proteinases of Helicoverpa armigera larvae by 87.51% and 76.12%, respectively, at concentration of 5 µg/mL with an IC50 of 1.75 µg/mL against trypsin like midgut proteinases. The enzyme kinetic studies demonstrated that MiTI is a competitive inhibitor with a K i value of 4.1 × 10(-10) M for Helicoverpa trypsin like midgut proteinases. In vivo experiments with different concentrations of MiTI in artificial diet (0.5, 1.0, and 1.5% w/w) showed an effective downfall in the larval body weight and an increase in larval mortality. The concentration of MiTI in the artificial diet to cause 50% mortality (LD50) of larvae was 1.5% w/w and that to cause reduction in mass of larvae by 50% (ED50) was 1.0% w/w. Nutritional indices observations suggest the toxic and adverse effects of MiTI on the growth and development of H. armigera larvae. The results suggest a strong bioinsecticidal potential of affinity purified MiTI which can be exploited in insect pest management of crop plants.