Field-evolved resistance to Bt maize by western corn rootworm.

Aaron J Gassmann,Ryan S Keweshan,Jennifer L Petzold-Maxwell,Mike W Dunbar,Peter Meyer

doi:10.1371/journal.pone.0022629

Abstract

BackgroundCrops engineered to produce insecticidal toxins derived from the bacterium Bacillus thuringiensis (Bt) are planted on millions of hectares annually, reducing the use of conventional insecticides and suppressing pests. However, the evolution of resistance could cut short these benefits. A primary pest targeted by Bt maize in the United States is the western corn rootworm Diabrotica virgifera virgifera (Coleoptera: Chrysomelidae).Methodology/Principal FindingsWe report that fields identified by farmers as having severe rootworm feeding injury to Bt maize contained populations of western corn rootworm that displayed significantly higher survival on Cry3Bb1 maize in laboratory bioassays than did western corn rootworm from fields not associated with such feeding injury. In all cases, fields experiencing severe rootworm feeding contained Cry3Bb1 maize. Interviews with farmers indicated that Cry3Bb1 maize had been grown in those fields for at least three consecutive years. There was a significant positive correlation between the number of years Cry3Bb1 maize had been grown in a field and the survival of rootworm populations on Cry3Bb1 maize in bioassays. However, there was no significant correlation among populations for survival on Cry34/35Ab1 maize and Cry3Bb1 maize, suggesting a lack of cross resistance between these Bt toxins.Conclusions/SignificanceThis is the first report of field-evolved resistance to a Bt toxin by the western corn rootworm and by any species of Coleoptera. Insufficient planting of refuges and non-recessive inheritance of resistance may have contributed to resistance. These results suggest that improvements in resistance management and a more integrated approach to the use of Bt crops may be necessary.

Highlights

Transgenic crops engineered to produce insecticidal toxins derived from the bacterium Bacillus thuringiensis (Bt) were planted on more than 58 million hectares worldwide in 2010 [1]
Survival was not significantly different between populations from problem fields and control fields on Cry34/35Ab1 maize (P = 0.95) or on non-Bt maize (P = 0.87). These results indicate that populations were susceptible to Cry34/35Ab1 maize, and that this Bt toxin significantly reduced survival
These data indicate that the western corn rootworm is evolving resistance to Cry3Bb1 maize in some populations in Iowa, USA

Summary

Introduction

Transgenic crops engineered to produce insecticidal toxins derived from the bacterium Bacillus thuringiensis (Bt) were planted on more than 58 million hectares worldwide in 2010 [1]. The western corn rootworm Diabrotica virgifera virgifera LeConte (Coleoptera: Chrysomelidae) is among the most serious pests of maize within the United States, with larval feeding on maize roots causing the majority of crop losses from this pest [7]. The evolution of resistance by the western corn rootworm could cut short the benefits of Bt maize. Crops engineered to produce insecticidal toxins derived from the bacterium Bacillus thuringiensis (Bt) are planted on millions of hectares annually, reducing the use of conventional insecticides and suppressing pests. A primary pest targeted by Bt maize in the United States is the western corn rootworm Diabrotica virgifera virgifera (Coleoptera: Chrysomelidae)

Methods

Results

Conclusion