Bioassays and binding tests between Cry toxins (Cry1Aa, Cry1Ab, Cry1Ac, and Cry2Ab) and brush-border membrane vesicles (BBMVs) from larvae of aBacillus thurningiensis (Bt)-susceptible (96S) and two Cry1Ac-resistant strains (BtR and LFR10) were conducted for investigating cross-resistance of Cry1Ac-resistant strains to Cry2Ab inHelicoverpa armigera (Hübner) (Lepidoptera: Noctuidae). The resistance ratio (RR) values of the BtR and LFR10 strains to Cry1Ac and Cry2Ab were 2,971- and 1.1-fold and 253- and 1.0-fold, respectively, indicating that there was no cross-resistance to Cry2Ab. The binding experiments between Cry toxins and BBMVs from BtR, LFR10, and 96S larvae showed that all of the toxins could bind with these BBMVs, but the Cry2Ab could not displace125I labeled Cry1Ac and Cry1Ab. The same results were observed in reciprocal binding tests, demonstrating that Cry1A and Cry2Ab had different binding sites inH.armigera and providing a potential mechanism for the lack of cross-resistance between Cry1A and Cry2Ab toxins. These results suggest that the transgenic cotton,Gossypium hirsutum L., expressingCry1Ac andCry2Ab genes may be deployed for management of Cry1Ac resistantH.armigera.
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Vol. 100 • No. 3