Deterioration of digestive physiology of Bactrocera cucurbitae larvae by trypsin inhibitor purified from seeds of Mucuna pruriens

Peptidase inhibitors (PIs) are plant proteins that are found to be effective against various digestive peptidases of insects. The present study isolated and characterized a trypsin inhibitor from mature dry seeds of Mucuna pruriens and investigated its effect against Bactrocera cucurbitae larvae, a major pest of cucurbitaceae crops, for its inhibitory activity. The purified trypsin inhibitor from M. pruriens seeds gave a molecular weight of ~11 kDa on SDS-PAGE. M. pruriens trypsin inhibitor (MPTI) exhibited inhibitory effect on growth of melon fruit fly larvae (64-72 h old) as it resulted in prolongation of larval, pupal and total development period. There was a significant increase in larval mortality with increase in concentration of MPTI. Nutritional indices decreased significantly at all the concentrations of MPTI. Quantitative RT- PCR revealed that the mRNA expression level of trypsin and chymotrypsin genes was reduced while that of GST, esterases, AP, SOD and catalase were enhanced. It can therefore be inferred that MPTI can serve as a promising agent for biocontrol that can reduce the problems caused by fruit fly and other similar catastrophic pests. This study provides the fundamental information for future successful strategies for pest management.

Keywords: Bactrocera cucurbitae; Gene expression; Mucuna pruriens; Trypsin inhibitor.