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Applied and Environmental Microbiology, October 2003, p. 5898-5906, Vol. 69, No. 10
0099-2240/03/$08.00+0     DOI: 10.1128/AEM.69.10.5898-5906.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.

Dual Resistance to Bacillus thuringiensis Cry1Ac and Cry2Aa Toxins in Heliothis virescens Suggests Multiple Mechanisms of Resistance

Juan Luis Jurat-Fuentes,1 Fred L. Gould,2 and Michael J. Adang1,3*

Departments of Entomology,1 Biochemistry and Molecular Biology, University of Georgia, Athens, Georgia 30602-2603,3 Department of Entomology, North Carolina State University, Raleigh, North Carolina 276952

Received 16 May 2003/ Accepted 1 August 2003

One strategy for delaying evolution of resistance to Bacillus thuringiensis crystal (Cry) endotoxins is the production of multiple Cry toxins in each transgenic plant (gene stacking). This strategy relies upon the assumption that simultaneous evolution of resistance to toxins that have different modes of action will be difficult for insect pests. In B. thuringiensis-transgenic (Bt) cotton, production of both Cry1Ac and Cry2Ab has been proposed to delay resistance of Heliothis virescens (tobacco budworm). After previous laboratory selection with Cry1Ac, H. virescens strains CXC and KCBhyb developed high levels of cross-resistance not only to toxins similar to Cry1Ac but also to Cry2Aa. We studied the role of toxin binding alteration in resistance and cross-resistance with the CXC and KCBhyb strains. In toxin binding experiments, Cry1A and Cry2Aa toxins bound to brush border membrane vesicles from CXC, but binding of Cry1Aa was reduced for the KCBhyb strain compared to susceptible insects. Since Cry1Aa and Cry2Aa do not share binding proteins in H. virescens, our results suggest occurrence of at least two mechanisms of resistance in KCBhyb insects, one of them related to reduction of Cry1Aa toxin binding. Cry1Ac bound irreversibly to brush border membrane vesicles (BBMV) from YDK, CXC, and KCBhyb larvae, suggesting that Cry1Ac insertion was unaffected. These results highlight the genetic potential of H. virescens to become resistant to distinct Cry toxins simultaneously and may question the effectiveness of gene stacking in delaying evolution of resistance.

* Corresponding author. Mailing address: Department of Entomology, University of Georgia, Athens, GA 30602-2603. Phone: (706) 542-2436. Fax: (706) 542-2279. E-mail: adang{at}uga.edu.

Applied and Environmental Microbiology, October 2003, p. 5898-5906, Vol. 69, No. 10
0099-2240/03/$08.00+0     DOI: 10.1128/AEM.69.10.5898-5906.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.



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