CHARACTERIZATION AND DISTRIBUTION OF DIGESTIVE PROTEASES OF THE STALKCORN-BORER, SESAMIA NONAGRIOIDES LEF (LEPIDOPTERA, NOCTUIDAE)

Larval midgut extracts from the noctuid Sesamia nonagrioides Lef. were assayed for protease activity. Total proteolytic activity, as measure d by azocasein hydrolysis, showed a pH optimum in the range 10.0 to 11 .5, suggesting a digestive system based largely on serine-like proteas es. The ability of midgut extracts to hydrolyze specific synthetic sub strates, the elucidation of the pH at which maximal hydrolysis occurs, and their sensitivity to protease inhibitors confirmed the presence o f the serine endoproteases: trypsin, chymotrypsin, and elastase; and t he exopeptidases: carboxypeptidase A, carboxypeptidase B, and leucine aminopeptidase. The distribution of these digestive proteases along th e gut sections and among the different midgut regions was examined. Al l types of endoproteases and exopeptidases were mainly located in the midgut, with less than 5% of the activity in the foregut and hindgut. When the two halves of the midgut were compared, all proteolytic activ ities were higher in the anterior portion of the midgut. Trypsin, chym otrypsin, elastase, and carboxypeptidase B activities were mainly loca ted in the endoperitrophic space of the midgut, with some activity in the ectoperitrophic space, whereas aminopeptidase and carboxypeptidase A activities were preferentially located in the midgut epithelium. (C ) 1996 Wiley-Liss, Inc.