Cross-resistance of Ostrinia furnacalis to Cry9Ee and Cry1Ab Proteins

Cry9Ee, a recently discovered toxin with high insecticidal activity against Ostrinia furnacalis(Guenee), is prospective for commercialization. Cry9 Ee and Cry1 Ab proteins were expressed, activated and purified, and tested against susceptive and Cry1Ab-resistant O. furnacalis to verify the cross-resistance of O. furnacalis to these two proteins. The results indicated that the LC50 of activated Cry9 Ee and Cry1 Ab to susceptible O. furnacalis were 3.04 and 0.89 μg/g, respectively. At 5.00 μg/g concentration, activated Cry9 Ee resulted in a 96% mortality rate against the Cry1Ab-resistant strain, which was comparable with its activity against the susceptible colony. The competition binding assay of the two proteins on BBMVs of O. furnacalis indicated no competition binding between Cry9 Ee and Cry1 Ab, showing that the two proteins use different receptors on the midgut of O. furnacalis. Therefore, there was no cross-resistance of O. furnacalis to Cry9 Ee and Cry1 Ab. Cry9 Ee gene may be an ideal candidate for next generation transgenic maize that can overcome or delay resistance of insect pests to transgenic maize.