In this study, two different colonies of O. nubilalis selected by chronic exposure to the Cry1Ab toxin from Bacillus thuringiensis, were studied to identify potential mechanism(s) of resistance. To indirectly assess the resistance mechanism in these colonies, bioassays were conducted to compare toxicity of both full-length versus truncated Cry1Ab and other Cry toxins. Initial results from bioassays suggested that the moderate levels of resistance (ca. 100-fold) that had developed in these colonies involves a modification of toxin-receptor interactions or possibly changes in gut proteases. Further biochemical assays were performed in order to assess protease activity and binding properties. Measurement of toxin binding to brush border membrane vesicles prepared from gut tissue was performed using Surface Plasmon Resonance technology. In one of the resistant colonies, altered receptor binding was identified as the Ka (association constant) from resistant colonies which differed from the control colony. However, the Kd (dissociation constant) were not significant different. Additionally, serine proteinases may also play a role in the resistance in these colonies, as their activities were different in all resistant colonies relative to the unselected control colony. The relative importance of gut proteinases and altered receptor binding has yet to be determined.
Species 1: Lepidoptera Crambidae Ostrinia nubilalis (European corn borer)
Keywords: Protease, Kinetics
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