REVERSAL OF RESISTANCE TO BACILLUS-THURINGIENSIS IN PLUTELLA-XYLOSTELLA

Continued success of the most widely used biopesticide, Bacillus thuri ngiensis, is threatened by development of resistance in pests. Experim ents with Plutella xylostella (diamondback moth), the first insect wit h field populations resistant to B. thuringiensis, revealed factors th at promote reversal of resistance. In strains of P. xylostella with 25 - to 2800-fold resistance to B. thuringiensis compared with unselected strains, reversal of resistance occurred when exposure to B. thuringi ensis was stopped for many generations. Reversal of resistance was ass ociated with restoration of binding of B. thuringiensis toxin CryIA(c) to brush-border membrane vesicles and with increased biotic fitness. Compared with susceptible colonies, revertant colonies had a higher pr oportion of extremely resistant individuals. Revertant colonies respon ded rapidly to reselection for resistance. Understanding reversal of r esistance will help to design strategies for extending the usefulness of this environmentally benign insecticide.