OCCURRENCE OF A COMMON BINDING-SITE IN MAMESTRA-BRASSICAE, PHTHORIMAEA-OPERCULELLA, AND SPODOPTERA-EXIGUA FOR THE INSECTICIDAL CRYSTAL PROTEINS CRYIA FROM BACILLUS-THURINGIENSIS

Specific binding to midgut membrane proteins is required for the toxic ity of insecticidal crystal proteins (ICP) from Bacillus thuringiensis , A direct relationship between toxicity and binding has been proposed , It has been hypothesized that sharing of a single receptor by more t han one ICP could lead to the occurrence of multiple resistance in the event of an alteration in the common receptor, Binding of CryIA(a), C ryIA(b) and CryIA(c), three structurally related ICPs, has been studie d in Phthorimaea operculella, Mamestra brassicae and Spodoptera exigua using brush border membrane vesicles (BBMV) from the midgut tissue, U sing iodinated CryIA(b), the three insects showed similar results: one binding site for CryIA(b), which is shared with CryIA(a) and CryIA(c) , The binding site concentrations obtained for CryIA(b) in P, opercule lla, M, brassicae and S, exigua were 5.1, 16.3 and 2.2 pmol/mg vesicle protein, respectively, In the same way, dissociation constants were 3 .8, 5.3 and 0.7 nM, Data show that binding for an ICP does not directl y imply toxicity. The occurrence of a common receptor for the CryIA su bgroup of ICPs in P, operculella, M, brassicae and S, exigua might the oretically discourage the use of combinations of these ICPs in integra ted pest management programmes, (C) 1997 Elsevier Science Ltd.