THE INFLUENCE OF A 21 kDa KUNITZ‐TYPE TRYPSIN INHIBITOR FROM NONHOST MADRAS THORN,Pithecellobium dulce,SEEDS ON H. armigera (HÜBNER) (LEPIDOPTERA: NOCTUIDAE)

A trypsin inhibitor purified from the seeds of the Manila tamarind, Pithecellobium dulce (PDTI), was studied for its effects on growth parameters and developmental stages of  Helicoverpa armigera. PDTI exhibited inhibitory activity against bovine trypsin (～86%; ～1.33 ug/ml IC₅₀). The inhibitory activity of PDTI was unaltered over a wide range of temperature, pH, and in the presence of dithiothreitol. Larval midgut proteases were unable to digest PDTI for up to 12 h of incubation. Dixon and Lineweaver–Burk double reciprocal plots analysis revealed a competitive inhibition mechanism and a K_i of ～3.9 × 10^?8 M. Lethal dose (0.50% w/w) and dosage for weight reduction by 50% (0.25% w/w) were determined. PDTI showed a dose‐dependent effect on mean larval weight and a series of nutritional disturbances. In artificial diet at 0.25% w/w PDTI, the efficiency of conversion of ingested food, of digested food, relative growth rate, and growth index declined, whereas approximate digestibility, relative consumption rate, metabolic cost, consumption index, and total developmental period were increased in larvae. This is the first report of antifeedant and antimetabolic activities of PDTI on midgut proteases of  H. armigera.