INTERACTIONS OF BACILLUS-THURINGIENSIS CRYSTAL PROTEINS WITH THE MIDGUT EPITHELIAL-CELLS OF SPODOPTERA-FRUGIPERDA (LEPIDOPTERA, NOCTUIDAE)

Binding of different Bacillus thuringiensis insecticidal crystal prote ins (ICPs) to the midgut epithelium of Spodoptera frugiperda larvae wa s characterized by binding experiments with midgut tissue sections and isolated brush border membrane vesicles. Our results show that ICPs i nteract with the microvilli of epithelial cells of S. frugiperda in tw o different ways. The first is typical of highly toxic proteins (like CryIC and CryID); this interaction is saturable and specific, In contr ast, some nontoxic proteins (like CryIAb) interact nonspecifically wit h the microvilli, since the binding of this toxin is not affected by t he presence of high concentrations of homologous competitor. The CryIC toxin binds to two brush border proteins of 40 and 44 kDa and the Cry IAb toxin binds to a single protein of 150 kDa. Immunological detectio n of ingested B. thuringiensis ICPs on gut sections of S. frugiperda l arvae revealed that CryIC and CryID toxins bound along the epithelial brush border microvilli membrane. Binding of the nontoxic protein CryI Ab was also observed in the epithelial brush border membrane of fed la rvae, but it was extremely weak, implying that this type of interactio n occurs also in vivo although it is not related to toxicity. (C) 1996 Academic Press, Inc.