Abstract
In some previously reported cases, transgenic crops producing insecticidal proteins from Bacillus thuringiensis (Bt) have suppressed insect pests not only in fields planted with such crops, but also regionally on host plants that do not produce Bt toxins. Here we used 16 years of field data to determine if Bt cotton caused this “halo effect” against pink bollworm (Pectinophora gossypiella) in six provinces of the Yangtze River Valley of China. In this region, the percentage of cotton hectares planted with Bt cotton increased from 9% in 2000 to 94% in 2009 and 2010. We found that Bt cotton significantly decreased the population density of pink bollworm on non-Bt cotton, with net decreases of 91% for eggs and 95% for larvae on non-Bt cotton after 11 years of Bt cotton use. Insecticide sprays targeting pink bollworm and cotton bollworm (Helicoverpa armigera) decreased by 69%. Previously reported evidence of the early stages of evolution of pink bollworm resistance to Bt cotton in China has raised concerns that if unchecked, such resistance could eventually diminish or eliminate the benefits of Bt cotton. The results reported here suggest that it might be possible to find a percentage of Bt cotton lower than the current level that causes sufficient regional pest suppression and reduces the risk of resistance.
Highlights
Transgenic corn and cotton producing insecticidal proteins from Bacillus thuringiensis (Bt) were planted on more than 66 million hectares worldwide in 2011 to control insect pests and reduce reliance on insecticide sprays [1,2].The primary threat to the continued success of these Bt crops is evolution of resistance by pests [3,4]
Compared with the five years before Bt cotton was grown in the Yangtze River Valley (1995– 1999), the population density of pink bollworm on non-Bt cotton decreased significantly during 11 years of Bt cotton use, with a net reduction of 91% for eggs and 95% for larvae (Fig. 3)
Because the Bt cotton percentage in the Yangtze River Valley increased from 62% in 2005 to 84% in 2006, the results here imply that the threshold for lower r is somewhere between these two values
Summary
Transgenic corn and cotton producing insecticidal proteins from Bacillus thuringiensis (Bt) were planted on more than 66 million hectares worldwide in 2011 to control insect pests and reduce reliance on insecticide sprays [1,2].The primary threat to the continued success of these Bt crops is evolution of resistance by pests [3,4]. One of the potential drawbacks of the refuge strategy is increased pest damage to non-Bt crop plants in refuges [11]. Bt crops suppress pest populations in Bt crop fields, and in nearby non-Bt crop fields [12,13,14,15,16,17,18,19] This ‘‘halo effect’’ was predicted on theoretical grounds, because females emerging from non-Bt crops lay some of their eggs on nearby Bt crops, and the larvae hatching from such eggs suffer high mortality on the Bt crops [12,13,14]. By reducing damage to non-Bt plants, the halo effect can reduce the need for insecticide sprays on non-Bt crops and encourage compliance with the refuge strategy, thereby increasing the benefits and sustainability of Bt crops [12,18]
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