Assessment of soybean inhibitor as a biopesticide against melon fruit fly, Bactrocera cucurbitae (Coquillett)

Abstract

In the current study, the soybean trypsin–chymotrypsin inhibitor (Bowman–Birk Inhibitor, SBBI) was tested against Bactrocera cucurbitae (Coquillett), a major pest of cucurbit crops. Bioassays conducted using different concentrations (12.5, 25, 50, 100 and 200 ppm) revealed a detrimental effect of the inhibitor on the growth and development of the second instar larvae of the melon fruit fly. SBBI prolonged the larval and total development period and reduced the percentage pupation and emergence. Enzymatic assays of proteases conducted at three time intervals using the LC40 (59 ppm) concentration of SBBI showed an inhibitory effect on trypsin activity, whereas an increase was observed in the activity of chymotrypsin, elastase and leucine aminopeptidase. Among the enzymes involved in detoxification, antioxidant and general metabolism, an increase was observed in the activity of catalases, and acid and alkaline phosphatases at most treatment intervals. The activity of esterases was induced only with prolonged treatment whereas that of glutathione S-transferases was suppressed in larvae treated with SBBI. The findings revealed the potential of SBBI to disrupt the growth of the melon fruit fly.