Occurrence of digestive cysteine proteases in Perillus bioculatus, a natural predator of the Colorado potato beetle

Oryzacystatins (OCs) are protease inhibitors (PIs) that inhibit Colorado potato beetle (CPB) digestive proteases, and transgenic potato plants containing these Pls are currently under test. However, OCs could interfere with the digestive system of beneficial insects. Protease activity and susceptibility to class-specific protease inhibitors were studied in protein extracts of Perillus bioculatus, a stinkbug predator that has shown potential for biological control of the CPB. At physiological pH, the analysis of protease activity showed that up to 90% of P. bioculatus protease activity is of the cysteine type. All active life stages of the predator were tested, and electrophoretic characterization detected no major qualitative variation in protease pattern between stages. Protease activity in extracts of P. bioculatus nymphs was significantly reduced, up to 70%, by the two recombinant cystatins from rice (OCI and OCII), and by stefin A, a PI encoded by a human gene. These results clearly indicate that cysteine PIs are active not only against the CPB digestive protease complex, but also against proteases of one of its most important natural predators. (C) 1998 Elsevier Science Inc. All rights reserved.