Resistance to Bacillus thuringiensis in Plutella xylostella

Insecticidal crystal proteins from Bacillus thuringiensis (Bt) offer safe, specific, and effective insect control. Evolution of resistance by pests is the greatest threat to the long-term effectiveness of Bt. The first insect to evolve resistance to Bt in open field populations is the diamondback moth ( Plutella xylostella ), a global pest of vegetables. Resistance to Bt has been found in some populations of diamondback moth from Hawaii, the continental United States, and several Asian nations. Resistance to Bt in diamondback moth is inherited as an autosomal, recessive trait and is associated with reduced binding of toxin to sites on the larval midgut membrane. Resistance to CryIA toxins from Bt subsp. kurstaki caused cross-resistance to CryIF, but not to CryIB or CryIC. In laboratory populations containing susceptible and resistant individuals, fitness costs associated with resistance promoted reversal of resistance in the absence of exposure to Bt. In an isofemale line derived from an extensively selected strain, >5,000-fold resistance persisted for >20 generations without selection, which shows that at least one resistant genotype is not inherently unstable. Field-evolved resistance to Bt in diamondback moth has provided a warning and an opportunity to gain knowledge essential for sustainable use of Bt.