Widespread use of genetically engineered Bt maize, designed to combat rootworm pests, has led to overplanting and pest resistance, jeopardizing the crop’s long-term effectiveness, according to a new study. The findings – informed by data from ten U.S. “Corn Belt” states – estimate that this overuse has cost U.S. farmers $1.6 billion in economic losses, emphasizing the need for improved seed diversity, transparency, and farmer decision-making to sustain transgenic crop benefits. “If current and future related innovations are managed as Bt maize hybrids have been,” say the authors, “we risk entering a cycle of rapid obsolescence among transgenic technologies…” Genetically engineered crops, particularly those incorporating insecticidal proteins from Bacillus thuringiensis (Bt), have significantly boosted global food production by reducing pest damage with minimal environmental impact. However, as the use of Bt crops increases, pests inevitably develop resistance, diminishing the effectiveness of the technology over time. Bt maize hybrids targeting corn rootworms have seen widespread use, but resistance began emerging in 2009, raising concerns about Bt maize’s long-term viability. The issue can be likened to the "tragedy of the commons," where individual actions based on self-interest lead to the overexploitation of a shared resource.

Leveraging 12 years of field trial data and farmers’ seed usage across 10 U.S. Corn Belt states, as well as an interdisciplinary approach distinguishing between self-interested decision-making and optical decisions that account for broader community impacts, Ziwei Ye and colleagues evaluated the economic consequences of diverging from optimal rootworm Bt maize planting levels. Ye et al. found that while pest pressure decreased as a result of pest suppression by Bt maize, increased planting of this crop has undermined its anti-rootworm effectiveness. Moreover, a cost-benefit analysis from 2014 to 2016 shows that Bt maize was often planted excessively, particularly in the eastern Corn Belt states, where pest pressure was low. This overuse led to minimal pest suppression benefits, higher costs for transgenic seed, and a significant depletion of the pest susceptibility pool, resulting in an estimated $1.6 billion in lifetime economic losses for growers in these regions. According to the authors, the findings highlight broader systemic issues driving Bt overuse. Discrepancies between planting for self-interests and the optical Bt planting levels are largely due to misperceptions about the overall costs and benefits of Bt maize. This is further complicated by bundled trait packages and market pressures from profit-driven seed companies. What’s more, farmers are often underinformed about rootworm pressures and the long-term implications of using Bt hybrids. “Addressing the challenges faced by regulators and raised by Ye et al. will require balancing short-term farmer incentives with long-term agricultural and environmental sustainability, ensuring that Bt crops remain viable tools for pest management,” write Zachary Brown and Dominic Reisig in a related Policy Forum.

Podcast: A segment of Science's weekly podcast with Christian Krupke, related to this research, will be available on the Science.org podcast landing page [www.science.org/podcasts] after the embargo lifts. Reporters are free to make use of the segments for broadcast purposes and/or quote from them – with appropriate attribution (i.e., cite "Science podcast"). Please note that the file itself should not be posted to any other Web site.