Activity of gut proteinases from Cry1Ab-selected colonies of the European corn borer, Ostrinia nubilalis (Lepidoptera: Crambidae)

Susceptibility to the Cry1Ab protoxin and toxin from Bacillus thuringiensis (Berliner) and activity of gut proteinases were assessed in both susceptible and Cry1Ab-selected colonies of European corn borer, Ostrinia nubilalis (Hubner). Resistance in two different selected colonies was at least 6- and 15-fold for the Cry1Ab protoxin and 108- and 484-fold for the Cry1Ab toxin. Activities of trypsin-like, chymotrypsin-like and elastase-like proteinases were variable among the colonies tested and not indicative of a major contribution to Cry1Ab resistance. Activation of the 130-kDa Cry1Ab protoxin occurred rapidly in all colonies, with no apparent differences among colonies. In addition, there were no apparent changes in activated Cry1Ab processing, indicating that proteolytic degradation was not associated with resistance. These results suggest that mechanisms other than proteolytic activation of protoxin and toxin degradation, such as target site modification may be involved in the resistance to B thuringiensis Cry1Ab in these O nubilalis colonies.