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Applied and Environmental Microbiology, January 2005, p. 185-189, Vol. 71, No. 1
0099-2240/05/$08.00+0     doi:10.1128/AEM.71.1.185-189.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

Cyt1A of Bacillus thuringiensis Delays Evolution of Resistance to Cry11A in the Mosquito Culex quinquefasciatus

Margaret C. Wirth,1 Hyun-Woo Park,1 William E. Walton,1 and Brian A. Federici1,2*

Department of Entomology,1 Interdepartmental Graduate Programs in Genetics and Microbiology, University of California, Riverside, Riverside, California2

Received 10 April 2004/ Accepted 6 August 2004

Insecticides based on Bacillus thuringiensis subsp. israelensis have been used for mosquito and blackfly control for more than 20 years, yet no resistance to this bacterium has been reported. Moreover, in contrast to B. thuringiensis subspecies toxic to coleopteran or lepidopteran larvae, only low levels of resistance to B. thuringiensis subsp. israelensis have been obtained in laboratory experiments where mosquito larvae were placed under heavy selection pressure for more than 30 generations. Selection of Culex quinquefasciatus with mutants of B. thuringiensis subsp. israelensis that contained different combinations of its Cry proteins and Cyt1Aa suggested that the latter protein delayed resistance. This hypothesis, however, has not been tested experimentally. Here we report experiments in which separate C. quinquefasciatus populations were selected for 20 generations to recombinant strains of B. thuringiensis that produced either Cyt1Aa, Cry11Aa, or a 1:3 mixture of these strains. At the end of selection, the resistance ratio was 1,237 in the Cry11Aa-selected population and 242 in the Cyt1Aa-selected population. The resistance ratio, however, was only 8 in the population selected with the 1:3 ratio of Cyt1Aa and Cry11Aa strains. When the resistant mosquito strain developed by selection to the Cyt1Aa-Cry11Aa combination was assayed against Cry11Aa after 48 generations, resistance to this protein was 9.3-fold. This indicates that in the presence of Cyt1Aa, resistance to Cry11Aa evolved, but at a much lower rate than when Cyt1Aa was absent. These results indicate that Cyt1Aa is the principal factor responsible for delaying the evolution and expression of resistance to mosquitocidal Cry proteins.

* Corresponding author. Mailing address: Department of Entomology, University of California, Riverside, Riverside, CA 92521. Phone: (951) 827-5006. Fax: (951) 827-3086. E-mail: brian.federici{at}ucr.edu.

Applied and Environmental Microbiology, January 2005, p. 185-189, Vol. 71, No. 1
0099-2240/05/$08.00+0     doi:10.1128/AEM.71.1.185-189.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

  • Wirth, M. C., Yang, Y., Walton, W. E., Federici, B. A., Berry, C. (2007). Mtx Toxins Synergize Bacillus sphaericus and Cry11Aa against Susceptible and Insecticide-Resistant Culex quinquefasciatus Larvae. Appl. Environ. Microbiol. 73: 6066-6071 [Abstract] [Full Text]  
  • Manasherob, R., Itsko, M., Sela-Baranes, N., Ben-Dov, E., Berry, C., Cohen, S., Zaritsky, A. (2006). Cyt1Ca from Bacillus thuringiensis subsp. israelensis: production in Escherichia coli and comparison of its biological activities with those of other Cyt-like proteins.. Microbiology 152: 2651-2659 [Abstract] [Full Text]  
  • Perez, C., Fernandez, L. E., Sun, J., Folch, J. L., Gill, S. S., Soberon, M., Bravo, A. (2005). Bacillus thuringiensis subsp. israelensis Cyt1Aa synergizes Cry11Aa toxin by functioning as a membrane-bound receptor. Proc. Natl. Acad. Sci. USA 102: 18303-18308 [Abstract] [Full Text]  
  • Itsko, M., Manasherob, R., Zaritsky, A. (2005). Partial Restoration of Antibacterial Activity of the Protein Encoded by a Cryptic Open Reading Frame (cyt1Ca) from Bacillus thuringiensis subsp. israelensis by Site-Directed Mutagenesis. J. Bacteriol. 187: 6379-6385 [Abstract] [Full Text]  


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