Bacillus thuringiensis crystal proteins CRY1Ab and CRY1Fa share a high affinity binding site in Plutella xylostella...

The future success of Bacillus thuringiensis based insecticides depends in part on our ability to prevent insects from developing resistance against their insecticidal crystal proteins. Two recent papers indicated cross-resistance between Cry1A proteins and Cry1Fa in two different insect species (Tabashnik et al., 1994, Appl. Environ. Microbiol. 60, 4627-4629; Gould et al., 1995, J. Econ. Entomol. 88, 1545-1559). Brush border membrane vesicles were prepared from Plutella xylostella and used in binding assays with 125I-labeled trypsin-activated crystal proteins. Competition experiments showed that Cry1Fa competed with Cry1Ab for a same binding site, though the latter still bound to a different minor binding site with apparently the same affinity. Cry1Ca did not compete for Cry1Ab binding sites nor Cry1Fa for Cry1Ca binding sites. Based on these results, a modification of the receptor shared by Cry1Ab and Cry1Fa might confer multiple resistance to Cry1A and Cry1Fa proteins.