Transgenic crops producing insecticidal proteins from Bacillus thuringiensis (Bt) have been grown commercially on millions of hectares since 1996. The primary threat to the continued success of such Bt crops is evolution of resistance by pests. Although many diamondback moth populations have evolved resistance to Bt sprays, as far as we know, no pest has evolved resistance in the field to a Bt crop. However, strains of many pests have been selected for resistance to Bt toxins in the laboratory. The most common pattern of Bt resistance in field- and lab-selected Lepidoptera, called "mode 1," entails >500-fold resistance to at least one Cry1A toxin, recessive inheritance, little or no cross-resistance to Cry1C, and reduced binding at least one Cry1A toxin. Whereas some resistant strains of diamondback moth and pink bollworm thrive on Bt plants, recent results show that a Dipel-resistant strain of European corn borer did not survive on Bt corn. With the notable exception of pink bollworm, estimates from field populations of the frequency of alleles conferring resistance to Bt plants have been close to or less than 0.001. In summary, the success of Bt crops exceeds the expectations of many, but does not preclude resistance problems in the future.
Species 1: Lepidoptera Gelechiidae Pectinophora gossypiella (pink bollworm)
Species 2: Lepidoptera Plutellidae Plutella xylostella (diamondback moth)
Species 3: Lepidoptera Crambidae Ostrinia nubilalis (European corn borer)
Keywords: Resistance management, transgenic crops
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