The use of oryzacystatins I and II, two cysteine proteinase inhibitors naturally produced in rice grains, represents an attractive way for the control of Coleoptera insect pests. The present study was done to analyze the inhibitory effect of recombinant oryzacystatins produced in Escherichia coli as fusion proteins against digestive proteinases of the major pest Colorado potato beetle (Leptinotarsa decemlineata Say). Both inhibitors had a significant effect on total proteolytic activity, but maximal inhibitions ranged from 20 to 80% for pHs varying from 5.0 to 7.0, respectively. This pH-dependent efficiency of plant cystatins was due to the selective inactivation of potato beetle cathepsin H, as demonstrated by the use of inhibitors with different specificities against cathepsins B and H. These results demonstrate the importance of having an adequate knowledge of insect proteinases specifically recognized by the inhibitors to be used in pest control strategies.
