RESUMO
Transgenic crops that produce insecticidal proteins from Bacillus thuringiensis (Bt) can suppress pests and reduce insecticide sprays, but their efficacy is reduced when pests evolve resistance. Although farmers plant refuges of non-Bt host plants to delay pest resistance, this tactic has not been sufficient against the western corn rootworm, Diabrotica virgifera virgifera In the United States, some populations of this devastating pest have rapidly evolved practical resistance to Cry3 toxins and Cry34/35Ab, the only Bt toxins in commercially available corn that kill rootworms. Here, we analyzed data from 2011 to 2016 on Bt corn fields producing Cry3Bb alone that were severely damaged by this pest in 25 crop-reporting districts of Illinois, Iowa, and Minnesota. The annual mean frequency of these problem fields was 29 fields (range 7 to 70) per million acres of Cry3Bb corn in 2011 to 2013, with a cost of $163 to $227 per damaged acre. The frequency of problem fields declined by 92% in 2014 to 2016 relative to 2011 to 2013 and was negatively associated with rotation of corn with soybean. The effectiveness of corn rotation for mitigating Bt resistance problems did not differ significantly between crop-reporting districts with versus without prevalent rotation-resistant rootworm populations. In some analyses, the frequency of problem fields was positively associated with planting of Cry3 corn and negatively associated with planting of Bt corn producing both a Cry3 toxin and Cry34/35Ab. The results highlight the central role of crop rotation for mitigating impacts of D. v. virgifera resistance to Bt corn.
Assuntos
Besouros/fisiologia , Produção Agrícola/métodos , Endotoxinas/farmacologia , Doenças das Plantas/parasitologia , Plantas Geneticamente Modificadas/imunologia , Zea mays/imunologia , Animais , Bacillus thuringiensis/genética , Bacillus thuringiensis/metabolismo , Besouros/efeitos dos fármacos , Produção Agrícola/economia , Endotoxinas/genética , Endotoxinas/metabolismo , Resistência a Inseticidas , Iowa , Controle Biológico de Vetores/economia , Doenças das Plantas/economia , Doenças das Plantas/imunologia , Doenças das Plantas/prevenção & controle , Plantas Geneticamente Modificadas/genética , Plantas Geneticamente Modificadas/parasitologia , Glycine max/crescimento & desenvolvimento , Zea mays/genética , Zea mays/crescimento & desenvolvimento , Zea mays/parasitologiaRESUMO
This study examines the impact of cover crop adoption on soil erosion levels in the United States (US) Midwest. Based on a novel county-level panel data set with information on soil erosion levels and remotely-sensed cover crop acreage, we estimate linear panel fixed effect econometric models and conduct a number of robustness checks to investigate the direct impact of cover crops on two major types of soil erosion (wind and water erosion). Although we find that counties with higher cover crop acreage have statistically lower soil erosion levels due to water, wind, or both, we believe that the magnitudes of the estimated effects are modest. Longer-term multi-year use of cover crops also do not seem to increase the soil erosion reducing effects of cover crops over time. Results from the empirical analysis provide further empirical evidence on the impact of cover crops on soil erosion based on data that captures farmer behavior at the county-level and covers a wider geographical region in the US. Our findings also give insights to policy makers in terms of further understanding the magnitude of the soil erosion benefits from cover crops.