Research shows that European corn borers in Minnesota and Wisconsin are developing resistance to Cry2Ab2, a key protein in genetically modified corn designed to protect crops from this pest. A 2026 study of 7,466 insects found that at least 15.09% of resistance genes are now present in wild populations—150 times higher than the safety threshold. This threatens the long-term effectiveness of Bt corn technology that has protected crops for nearly 30 years.
Scientists discovered that European corn borers in Minnesota and Wisconsin are developing resistance to a key type of genetically modified corn designed to protect crops from this pest. According to Gram Research analysis, researchers tested thousands of insects and found that resistance genes are becoming more common in wild populations. This is concerning because farmers rely on these special corn varieties to prevent billions of dollars in crop damage. The findings suggest that the technology farmers have used successfully for nearly 30 years may be losing its effectiveness against this particular pest, which could force changes in how farmers protect their crops.
Key Statistics
A 2026 research article analyzing 7,466 European corn borers from Minnesota and Wisconsin found that 21 of 84 tested families carried resistance genes to Cry2Ab2, with an estimated resistance allele frequency of at least 15.09%—exceeding safe thresholds by 150-fold.
According to research reviewed by Gram, resistance to Cry2Ab2 Bt protein in corn borer populations has increased from essentially zero in 1996 to at least 15.09% by 2024, demonstrating rapid adaptation to genetically modified crops in just 28 years.
A 2026 study of Midwest corn borer populations found that approximately 25% of tested families (21 out of 84) carried resistance genes to Cry2Ab2, suggesting that pyramided Bt corn may function as single-trait protection against this pest.
Research from 2024 field collections in Minnesota and Wisconsin indicates that Cry2Ab2 resistance in corn borers exceeds the 0.1% safety threshold by more than 150-fold, potentially compromising the redundant killing strategy underlying modern Bt corn technology.
The Quick Take
- What they studied: Whether corn borers in the Midwest are developing resistance to Bt corn, a genetically modified crop that produces a natural pesticide to kill this insect pest.
- Who participated: Scientists collected 84 families of European corn borers from multiple locations across Minnesota and Wisconsin in 2023 and 2024. They bred these wild insects with laboratory insects and tested 7,466 baby insects total.
- Key finding: About 25% of the tested families (21 out of 84) carried resistance genes to Cry2Ab2, the main Bt protein used in corn. The resistance gene frequency was at least 15.09%, which is significantly higher than the safety threshold of 0.1%.
- What it means for you: If you live in a farming region, this research suggests that the genetically modified corn protecting crops from corn borers may become less effective over time. Farmers may need to adopt new pest management strategies to maintain crop protection and prevent yield losses.
The Research Details
Researchers collected corn borers from farms across Minnesota and Wisconsin and brought them to the laboratory. They crossed these wild insects with insects that had never been exposed to Bt corn, creating a second generation (called F2 families). This breeding approach helps scientists detect hidden resistance genes that might not show up in the original insects.
The scientists then exposed 7,466 baby insects from these families to Cry2Ab2 protein—the same protein found in genetically modified corn. They used a special diet-overlay method where insects eat food containing the Bt protein. By counting how many insects survived this exposure, researchers could estimate how common resistance genes are in wild populations.
This approach is like a genetic detective test. If a family has resistance genes, some of the baby insects will survive the Bt protein exposure. By tracking which families had survivors, scientists can estimate how widespread resistance is becoming in nature.
This research method is important because it catches resistance before it becomes a major problem in fields. By testing wild populations now, scientists can warn farmers about emerging threats and help develop new strategies before crop damage becomes severe. The F2 screen method is considered the gold standard for detecting resistance genes early.
This study has several strengths: it tested a large number of insects (7,466), collected samples from multiple locations across two years, and used established scientific methods for detecting resistance. The research was published in a peer-reviewed journal focused on agricultural pest management. However, the study focused only on two Midwest states, so results may not apply to all corn-growing regions. The researchers also note that their estimates represent minimum resistance frequencies, meaning actual resistance could be even higher.
What the Results Show
The most striking finding is that resistance to Cry2Ab2 is already present in wild corn borer populations in Minnesota and Wisconsin. Out of 84 families tested, 21 families (about 25%) showed evidence of carrying resistance genes. This means that at least 15.09% of the genes in these populations are resistant versions—far exceeding the 0.1% threshold that scientists consider safe for maintaining Bt corn effectiveness.
To put this in perspective, when Bt corn was first introduced in 1996, resistance was essentially nonexistent in wild populations. The fact that it has reached 15% or higher in just 28 years shows how quickly insects can adapt to this technology. This is particularly concerning because the resistance appears to be spreading despite farmers following recommended practices for slowing resistance development.
The research also revealed that resistance is not limited to one location or one year. Multiple families from different collection sites showed resistance, suggesting this is a widespread problem across the region, not just an isolated incident. This geographic spread indicates that resistance genes are becoming established in the general population rather than appearing randomly.
The study found that resistance to Cry2Ab2 appears to be developing independently of resistance to other Bt proteins. This is important because farmers often plant corn with multiple Bt proteins (called pyramided Bt corn) specifically to prevent resistance. If insects can develop resistance to one protein without developing resistance to others, the backup protection may fail faster than expected. The research suggests that the redundant killing strategy—relying on multiple proteins to kill resistant insects—may not work as well as scientists hoped for this particular pest.
This research confirms concerns raised by earlier reports of practical resistance in Nova Scotia (Canada) and Connecticut (US) between 2018 and 2023. Those cases showed that corn borers could survive Bt corn in real farm fields. This new study provides the first detailed genetic evidence that resistance is spreading through wild populations in the major corn-growing region of the Midwest. The resistance frequency found here (15.09%) is much higher than what was detected in earlier studies, suggesting the problem is accelerating.
The study focused only on Minnesota and Wisconsin, so results may not apply to other corn-growing states or regions. The researchers tested only one Bt protein (Cry2Ab2) and did not examine resistance to other Bt proteins used in corn. Additionally, the study provides minimum estimates of resistance frequency—actual resistance could be higher than reported. The research also does not explain why resistance is developing so rapidly or identify the specific genetic changes causing resistance. Finally, the study was conducted in 2023-2024, so resistance frequencies may have changed since data collection.
The Bottom Line
Farmers in Minnesota and Wisconsin should consider rotating Bt corn with non-Bt corn varieties and using other pest management methods (like insecticides or biological controls) to reduce reliance on Bt technology alone. This is a high-confidence recommendation based on the high resistance frequencies detected. Farmers should also monitor their fields closely for corn borer damage and report any unusual pest pressure to agricultural extension services. Agricultural researchers should accelerate development of new pest management strategies and alternative Bt proteins that corn borers have not yet adapted to.
This research is most relevant to corn farmers in Minnesota, Wisconsin, and the broader Midwest corn belt. Agricultural extension services and pest management professionals should use this information to update their recommendations. Seed companies developing new corn varieties need to consider this resistance data when designing future products. Environmental regulators and policymakers should be aware that a major agricultural technology may be losing effectiveness. Consumers should understand that this may eventually affect corn prices and food costs, though the impact will likely be gradual.
Resistance is already affecting some farms, as evidenced by practical resistance reports in other regions. However, widespread crop damage from resistant corn borers may take 3-5 years to become obvious across the Midwest. The key window for action is now—farmers who implement resistance management strategies immediately can help slow the spread and maintain Bt corn effectiveness longer. Without intervention, scientists predict that Bt corn could become largely ineffective against corn borers within 10-15 years.
Frequently Asked Questions
Is Bt corn still effective against corn borers?
Bt corn remains effective for most corn borers, but effectiveness is declining in Minnesota and Wisconsin where resistance genes now affect at least 15% of wild populations. Farmers should combine Bt corn with other pest management methods to maintain protection.
What does Bt corn resistance mean for farmers?
Farmers may see increased corn borer damage over time, requiring additional pest management costs. They should rotate between Bt and non-Bt corn varieties, use insecticides when needed, and monitor fields closely for damage to maintain crop yields.
How did corn borers develop resistance to Bt corn so quickly?
Insects reproduce rapidly and have short lifespans, allowing beneficial mutations to spread through populations quickly. Widespread planting of the same Bt corn for 28 years created strong pressure favoring insects with resistance genes, accelerating adaptation.
Will this affect corn prices and food costs?
If Bt corn becomes less effective, farmers may spend more on pest management, potentially increasing corn prices gradually. However, new pest management strategies are being developed to prevent major crop losses and price spikes.
What should I do if I farm corn in the Midwest?
Implement crop rotation using both Bt and non-Bt corn varieties, scout fields regularly for corn borer damage, use insecticides when damage exceeds economic thresholds, and consult local agricultural extension services for updated pest management recommendations.
Want to Apply This Research?
- Track corn borer damage in your fields weekly during growing season by counting damaged plants per 100 plants. Compare damage levels year-to-year to detect if resistance is increasing in your area. Record which corn varieties you planted and their Bt protein types to identify patterns.
- Implement a crop rotation plan: alternate Bt corn with non-Bt corn varieties or other crops each season. Use the app to schedule reminders for scouting fields for corn borer damage and to log pest management actions taken (insecticide applications, biological controls, variety selection).
- Set up a multi-year tracking system comparing pest pressure across different corn varieties and management practices. Document which Bt proteins you use each year and correlate with damage levels. Share anonymized data with local agricultural extension services to help build regional resistance monitoring networks.
This article summarizes scientific research about corn borer resistance to Bt crops. It is not agricultural advice. Farmers should consult with local agricultural extension services, agronomists, and pest management professionals before making decisions about crop varieties, pest management strategies, or pesticide applications. Resistance patterns may vary by location and change over time. Always follow label instructions for any pesticides or agricultural products used.
This research translation is published by Gram Research, the science division of Gram, an AI-powered nutrition tracking app.