Mechanisms of inducible resistance against Bacillus thuringiensis endotoxins in invertebrates

Abstract Resistance in insect pests against the endotoxin of Bacillus thuringiensis (Berliner) (Bt) is a major threat to the usefulness of this biopesticide, both used as traditional formulations and in transgenic crops. A crucial requirement for the development of successful resistance management strategies is a molecular understanding of the nature and inheritance of resistance mechanisms. This information can be used to design management strategies that will delay or counteract Bt resistance. The best known Bt resistance mechanism is inactivation of brush border membrane receptors. This type of resistance has a largely recessive mode of inheritance, which has enabled the design of resistance management approaches involving high dose and refuge strategies. Recent observations suggest that other resistance mechanisms are possible, including a mechanism that sequesters the toxin in the gut lumen through inducible immune reactions. The elevated immune status associated with tolerance to the toxin can be transmitted to subsequent generations by a maternal effect, which has implications for resistance management in the field. The high dose/refuge strategy may not be appropriate for the management of these alternative resistance mechanisms and other strategies have to be developed if inducible dominant resistance or tolerance mechanisms occur frequently in the field.