Resistance of Western Corn Rootworm to Bt Corn: Data from the Laboratory and Field

The widespread planting of crops engineered to produce insecticidal toxins derived from the bacterium Bacillus thuringiensis (Bt) places intense selective pressure on pest populations to develop resistance.  Western corn rootworm is a key pest of corn and is managed through planting of Bt corn.   Beginning in 2009, fields were identified in Iowa, USA in which western corn rootworm imposed severe injury to Bt corn.  Subsequent laboratory analysis of these field populations revealed resistance to corn producing Bt toxins Cry3Bb1 and mCry3A, and cross-resistance between these toxins.  Experiments conducted in fields identified as harboring Cry3Bb1-resistant western corn rootworm found increased injury to Cry3Bb1 corn and increased survival of western corn rootworm on Cry3Bb1 corn, as compared with Cry34/35Ab1 corn, a type of Bt corn to which western corn rootworm remains susceptible.  Laboratory experiments with a Cry3Bb1-resistant strain of western corn rootworm indicated that resistance to Bt corn may not impose substantial fitness costs.  These data highlight the vulnerability of Bt corn to further evolution of resistance by western corn rootworm; and more broadly, point to the potential of insects to develop resistance rapidly when Bt crops do not achieve a high dose.  Efforts to preserve the efficacy of Bt corn for management of rootworm should emphasize the use Bt corn within a broader context of integrated pest management.