The widespread adoption of genetically engineered (GE) crops has clearly led to changes in pesticide use, but the nature and extent of these impacts remain open questions. We study this issue with a unique, large, and representative sample of plot-level choices made by U.S. maize and soybean farmers from 1998 to 2011. On average, adopters of GE glyphosate-tolerant (GT) soybeans used 28% (0.30 kg/ha) more herbicide than nonadopters, adopters of GT maize used 1.2% (0.03 kg/ha) less herbicide than nonadopters, and adopters of GE insect-resistant (IR) maize used 11.2% (0.013 kg/ha) less insecticide than nonadopters. When pesticides are weighted by the environmental impact quotient, however, we find that (relative to nonadopters) GE adopters used about the same amount of soybean herbicides, 9.8% less of maize herbicides, and 10.4% less of maize insecticides. In addition, the results indicate that the difference in pesticide use between GE and non-GE adopters has changed significantly over time. For both soybean and maize, GT adopters used increasingly more herbicides relative to nonadopters, whereas adopters of IR maize used increasingly less insecticides. The estimated pattern of change in herbicide use over time is consistent with the emergence of glyphosate weed resistance.
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机译：转基因作物的广泛采用显然导致了农药使用的变化，但是这些影响的性质和程度仍然是一个悬而未决的问题。我们使用1998年至2011年美国玉米和大豆种植者在田间选择的独特，大而有代表性的样本研究了这个问题。平均而言，耐草甘膦（GT）的GE大豆的采用者平均使用了28％（0.30 kg / ha）除草剂比不采用除草剂的人多，GT玉米的采用者除草剂比不采用的人少1.2％（0.03 kg / ha），GE抗虫（IR）玉米的采用者除草剂比不采用的人少11.2％（0.013 kg / ha）。但是，当农药受到环境影响商的加权时，我们发现（相对于非采用者）GE采纳者所使用的大豆除草剂用量大致相同，玉米除草剂用量减少9.8％，玉米杀虫剂用量减少10.4％。此外，结果表明，GE使用者和非GE使用者之间农药使用的差异已随时间发生了显着变化。对于大豆和玉米，GT的采用者相对于非采用者使用的除草剂越来越多，而IR玉米的采用者使用的杀虫剂越来越少。估计除草剂使用随时间变化的模式与草甘膦杂草抗性的出现相一致。
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