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Summary
This chapter examines the evolving relationship between pesticide use and the adoption of genetically engineered (GE) crops. Pesticides remain a central damage-control input in agriculture, delivering significant productivity and food-security benefits, yet their use is known to be associated with human health and environmental risks. Within this context, GE crops commercialized to date—primarily with insect-resistant (IR) and herbicide-tolerant (HT) traits—have fundamentally altered pest and weed management practices. Adoption of IR traits has provided farmers with insect control tool alternatives to insecticides, which tends to reduce pesticide treatments. By contrast, HT crops are designed to complement specific broad-spectrum herbicides (glyphosate, in most cases), while potentially substituting for other compounds. We briefly review and discuss the main empirical studies on the interaction between GE crop adoption and pesticide use, and also provide detailed descriptive evidence on the evolution of pesticide use, since the introduction of GE crops, in four main U.S. crops: corn, cotton, soybeans, and wheat. The evidence suggests that IR crop adoption has led to persistent reductions in insecticide use and, in many cases, improved yields and farm profits. These benefits extend beyond adopters through regional pest suppression, although they are increasingly challenged by the evolution of pest resistance. The impacts of HT crops on herbicide use are more complex and dynamic. Early adoption was characterized by large substitution toward glyphosate and, in some cases, reductions in overall herbicide mass and toxicity. Over time, however, widespread glyphosate resistance has induced renewed use of multiple herbicides, raising application rates, costs, and management complexity, and in some cases reversing earlier environmental gains. These dynamics underscore the limitations of simple mass-based pesticide measures and the need to rely on toxicity-weighted metrics. The chapter further reviews evidence on indirect environmental effects, human health implications—particularly surrounding glyphosate exposure—and regulatory responses. Overall, the analysis highlights that the impacts of GE crops on pesticide use and the associated externalities are inherently dynamic and context-dependent. Assessments based on aggregate trends, or slanted towards early adoption patterns, can be misleading. As novel genomic techniques emerge to promise a new generation of GE products, understanding the substitution and complementarity effects between crop protection technologies and GE crops remains central for informed policy design and welfare analysis.