INSECT RESISTANCE TO BACILLUS-THURINGIENSIS - UNIFORM OR DIVERSE

Resistance to the insecticidal proteins produced by the soil bacterium Bacillus thuringiensis (Bt) has been documented in more than a dozen species of insect. Nearly all of these cases have been produced primar ily by selection in the laboratory, but one pest, the diamondback moth (Plutella xylostella), has evolved resistance in open-field populatio ns. Insect resistance to Bt has immediate and widespread significance because of increasing reliance on Bt toxins in genetically engineered crops and conventional sprays. Furthermore, intense interest in Bt pro vides an opportunity to examine the extent to which evolutionary pathw ays to resistance vary among and within species of insect. One mode of resistance to Bt is characterized by more than 500-fold resistance to at least one Cry1A toxin, recessive inheritance, little or no cross-r esistance to Cry1C, and reduced binding of at least one Cry1A toxin. A nalysis of resistance to Bt in the diamondback moth and two other spec ies of moths suggests that although this particular mode of resistance may be the most common, it is not the only means by which insects can attain resistance to Bt.