Cassia fistula seed's trypsin inhibitor(s) as antibiosis agent in Helicoverpa armigera pest management

Inhibitors from diverse sources are being explored for understanding their inhibitory potential. Among several alternatives, protease inhibitors represent an attractive class of biopesticides with several important features. Such protease inhibitors are environmentally friendly and can work as defence molecules against plant pest and pathogens. Trypsin inhibitors CFTI-1 and CFTI-2 were purified from the seeds of the Cassia fistula and the prominent inhibitor CFTI-1 was studied for its effects on growth parameters and developmental stages of Helicoverpa armigera. CFTI-1 and CFTI-2 exhibited 92% and 78% inhibitory activity against midgut trypsin like proteases, respectively. Dixon and Lineweaver–Burk double reciprocal plots analysis revealed a competitive inhibition pattern with the Ki values 2.9×10−10 M and 4.2×10−10 M for CFTI-1 and CFTI- 2 respectively. Lethal concentration (0.34% m/m) and concentration for weight reduction by 50% (0.24% m/m) determined for CFTI-1. CFTI-1 showed a concentration-dependent effect on mean larval weight, a decline of the fertility and fecundity of the moths, and an extended total developmental duration of H. armigera life cycle. These results suggest that CFTI-1 has toxic and adverse effect on the developmental physiology of H. armigera and could be useful in controlling the pest H. armigera.