MODE OF ACTION OF BACILLUS-THURINGIENSIS TOXIN CRYIIIA - AN ANALYSIS OF TOXICITY IN LEPTINOTARSA-DECEMLINEATA (SAY) AND DIABROTICA-UNDECIMPUNCTATA-HOWARDI BARBER

Bacillus thuringiensis (Bt) strain EG2158 has vastly different levels of toxicity to Leptinotarsa decemlineata (Say) and Diabrotica undecimpunctata howardi Barber. L. decemlineata is at least 2000 fold more sensitive to EG2158 (which produces the insecticidal crystal protein CryIIIA) than D. undecimpunctata howardi. Therefore, at least one of the steps in the mode of action of CryIIIA must be altered in D. undecimpunctata howardi. Analysis of ingestion, solubilization and proteolytic digestion of CryIIIA did not demonstrate that these steps could account for the insensitivity of D. undecimpunctata howardi to CryIIIA. Instead, D. undecimpunctata howardi brush border membrane vesicles exhibited significant reduction in both reception of CryIIIA and in membrane permeability to water induced by CryIIIA. These data suggest that the relative failure of CryIIIA in D. undecimpunctata howardi is due, in part, to the poor ability of CryIIIA to bind to membrane receptors and to enhance membrane permeability.