The billion-dollar blunder: How overplanting GMO corn is costing farmers and fueling pest resistance
By willowt // 2025-03-04
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  • A study in Science reveals that U.S. farmers, particularly in the eastern Corn Belt, have overplanted genetically modified (GM) Bt corn, designed to repel pests like the corn rootworm. This overuse has caused significant economic losses — estimated at $1 billion — and accelerated pest resistance, undermining the technology's effectiveness.
  • Overplanting Bt corn has driven pests to evolve resistance, creating a cycle where farmers increasingly rely on more chemicals or new genetic modifications. Corn rootworm resistance to Bt corn has been documented in at least six U.S. states, with 29 cases of resistance reported globally across 11 pest species.
  • Seed companies often bundle multiple genetic traits into single seeds, making it difficult for farmers to assess costs and necessity. Industry consolidation has reduced farmers' choices, forcing them to adopt seeds with unnecessary traits and driving up costs.
  • The study advocates for clearer labeling of seed traits, government incentives for diverse seed options and practices like crop rotation and planting non-GM "refuges" to slow pest resistance. These measures aim to promote a more sustainable and balanced agricultural system.
  • The issues with Bt corn extend beyond the U.S., as seen in Mexico’s efforts to protect native maize from GMO contamination. Mexico’s government has moved to phase out GMO corn imports and glyphosate, highlighting the cultural, ecological and food security risks posed by GM crops.
In the heart of America’s Corn Belt, a quiet crisis is unfolding. A new study published in Science reveals that U.S. farmers have overplanted genetically modified (GM) corn, leading to staggering economic losses and a troubling rise in pest resistance. The findings underscore the unintended consequences of relying too heavily on a single agricultural technology — and the urgent need for a more diversified approach to farming.

The rise and fall of Bt corn

Genetically modified Bt corn, engineered to produce toxins from the bacterium Bacillus thuringiensis, was once hailed as a revolutionary solution to pest problems. First introduced in the 1990s, Bt corn was designed to repel pests like the corn rootworm, reducing the need for chemical insecticides. By 2025, more than 85% of U.S. corn crops were Bt varieties, a testament to their initial success. But nature has a way of adapting. Over time, pests like the corn rootworm have developed resistance to the toxins in Bt corn, rendering the technology less effective. The new study, which analyzed data from 10 states between 2005 and 2016, found that farmers in the eastern Corn Belt — particularly in Indiana, Ohio and Michigan — planted far more Bt corn than necessary. In some cases, farmers planted 50% of their fields with Bt corn, despite evidence suggesting that 18% or less would have been optimal. “This study is the first to show that short-term economic gains for individual farmers are associated with planting less Bt corn targeting rootworms,” said Bruce Tabashnik, a University of Arizona professor not involved in the research. The financial toll is staggering. If farmers in these states had adhered to the optimal planting levels, they could have saved 99 million annually between 2014 and 2016. Instead, overplanting has contributed to an estimated 1 billion in losses across the Corn Belt.

The pesticide treadmill: A vicious cycle

The overuse of Bt corn has not only hurt farmers’ wallets but also accelerated the evolution of resistant pests. “When you plant more Bt corn than necessary, you move the pest toward the evolution of resistance,” said Christian Krupke, a Purdue University entomologist and the study’s corresponding author. This phenomenon, often referred to as the “pesticide treadmill,” occurs when pests develop resistance to a technology, forcing farmers to rely on even more chemicals or new genetic modifications. The study warns that the current trajectory could lead to a “biotechnology version of the pesticide treadmill,” where innovations become obsolete at an alarming rate. Already, corn rootworm resistance to Bt corn has been documented in at least six U.S. states, and 29 cases of resistance to Bt crops have been reported globally across 11 pest species in seven countries. As resistance grows, farmers are increasingly turning back to synthetic insecticides — ironically, the very chemicals Bt corn was meant to replace.

A call for transparency and diversification

The study’s authors argue that the solution lies in greater transparency and diversification. Seed companies often “stack” multiple genetic traits — such as pest resistance and herbicide tolerance — into a single seed, making it difficult for farmers to assess the cost and necessity of each trait. This lack of clarity, combined with the consolidation of the seed industry, leaves farmers with fewer choices and higher costs. “Seed companies driven by profit maximization tend to strategically combine traits and genetics,” the study states. “As seed industry consolidation continues, U.S. farmers face a narrowing list of seed vendors and may be compelled to adopt varieties with unnecessary traits.” To address these challenges, the authors propose clearer labeling of seed traits and government incentives to encourage seed companies to offer more diverse and tailored options. They also emphasize the importance of practices like crop rotation and planting “refuges” of non-GM corn to slow the evolution of pest resistance.

A global perspective: Mexico’s fight against GMO contamination

The issues surrounding Bt corn are not confined to the U.S. In Mexico, the birthplace of maize, the spread of GM corn has sparked a fierce debate over food sovereignty and cultural heritage. Corn is central to Mexican agriculture, cuisine and identity, and the government has taken bold steps to protect native varieties from GMO contamination. In 2020, then-president Andrés Manuel López Obrador announced plans to phase out GMO corn imports and the herbicide glyphosate. While the policy has faced pushback from the U.S., Mexico’s current administration remains committed to restricting GMO corn in human food products. “Corn is one of the most important crops in the world, and Mexico is its center of origin,” said a spokesperson for the Non-GMO Project. “GMO contamination is a severe threat to biodiversity, food security and cultural heritage.”

Looking ahead: A sustainable path forward

The story of Bt corn serves as a cautionary tale about the risks of over-reliance on a single technology. While GM crops have undoubtedly brought benefits, their misuse has led to significant economic and environmental costs. As the study’s authors conclude, protecting the future of agriculture will require a more balanced approach — one that prioritizes transparency, diversity and sustainability. For farmers, policymakers and consumers alike, the message is clear: Nature always finds a way, so natural approaches are better. It’s time to rethink our relationship with GM crops and embrace solutions that work with nature, not against it. Sources include: ChildrensHealthDefense.org Science.org NonGMOProject.org
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