Lack of cross‐resistance to otherBacillus thuringiensiscrystal proteins in a population ofPlutella xylostellahighly resistant to cryia(b)

Competition experiments were performed with brush border membrane vesicles of diamondback moth larvae using 125I‐labelled CryIA(b) and unlabelled CryIA(a), CryIA(b) and CryIA(c). The results suggested a model with a single binding site for CryIA(b). Heterologous competition showed that CryIA(c) competed as effectively as CryIA(b) for the CryIA(b) binding site, whereas CryIA(a) competed less effectively. Toxicity tests were performed on third instar larvae with trypsin‐activated insecticidal crystal proteins (ICPs) and a commercial formulation of Bacillus thuringiensis (Bt) (Dipel). A laboratory colony was found to be susceptible to all four ICPs tested and to Dipel. CryIA(b), CryIA(c) and C…