Journal
PESTICIDE BIOCHEMISTRY AND PHYSIOLOGY
Volume 85, Issue 2, Pages 104-109Publisher
ACADEMIC PRESS INC ELSEVIER SCIENCE
DOI: 10.1016/j.pestbp.2005.11.003
Keywords
Helicoverpa armigera; Cry1A toxins; binding site; binding model; resistance
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Evolution of resistance by pests is the greatest threat to the continuous success of the Bacillus thuringiensis (Bt) toxins used in conventional sprays or in transgenic plants. The most common mechanism of insect resistance to Bt is reduced binding of toxins to target sites in the brush border membrane of the larval mid-gut. In this paper, binding experiments were performed with three I-125-Cry1A toxins and the brush border membrane vesicles from Cry1Ac resistant or susceptible strains of Helicoverpa armigera. The homologous competition test showed that there was no significant difference in Cry1Ac-binding affinity, but the concentration of Cry1Ac-binding sites dramatically decreased in the resistant strain (R-t decreased from 5.87 +/- 1.40 to 2.23 +/- 0.80). The heterologous competition test showed that there were three Cry1Ac-binding sites in the susceptible strain. Among them, site I bound with all three Cry1A toxins, site 2 bound with both Cry1Ab and Cry1Ac, and site 3 only bound with Cry1Ac. In the Cry1Ac resistant strain, the binding capability of site 1 with Cry1Ab decreased and site 2 did not bind with Cry1Ac. It is suggested that the absence of one binding site is responsible for H. armigera resistance to Cry1Ac. This result also showed that the resistance fitted the mode 1 pattern of Bt resistance described previously. (c) 2005 Elsevier Inc. All rights reserved.
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