摘要:Controversies over genetically engineered (henceforth GE or GMO) crops still remain because of uncertainties regarding their long term impact on pesticide use and on the environment if weeds and insects develop resistance to them. Updated USDA data on pesticide use and GMO adoption rates enable us to present a comprehensive analysis that spans 20 years –from 1986 to 2006- for two major crops that have benefited from intensive bioengineering research in the United States: corn and soybeans. After adjusting for the inherent heterogeneity across states and over time in the composition of herbicides and insecticides applied, results suggest that GE crops have lead to a decrease in the use of quality-adjusted pesticides with significant differences between herbicides and insecticides.