Corn Borer Damage Detected in Minnesota Bt Corn

First report of European corn borer infestation in Bt corn plants in the state raises concerns about potential resistance.

Apr. 15, 2026 at 8:19am

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Researchers from the University of Minnesota have reported the first documented cases of European corn borer (ECB) damage in Bt corn plants in the state. The discovery of ECB feeding in two Bt corn plants, which tested positive for the Cry1A and Cry2A proteins, suggests the pest may be developing resistance to common Bt traits used in genetically modified corn.

Why it matters

The emergence of ECB resistance to Bt corn could have major implications for Minnesota's corn growers, who have relied on the technology to effectively control this destructive pest for nearly three decades. Monitoring for resistance is crucial to develop appropriate management strategies and preserve the long-term viability of Bt corn.

The details

During a statewide survey in October 2025, researchers found ECB feeding damage in two Bt corn plants in a Minnesota field. Both plants tested positive for the Cry1A and Cry2A proteins, indicating the borer was able to survive and feed on the genetically modified corn. Additional plants in the same field showed more extensive ECB damage, but those were identified as non-Bt refuge plants. No larvae were recovered from the Bt plants, but two were found in the non-Bt plants, including one inside an ear of corn.

  • The statewide ECB survey was conducted during the first week of October 2025.
  • ECB resistance to the Cry1F Bt toxin was first confirmed in Nova Scotia, Canada in 2018.
  • ECB resistance to other Cry1 Bt toxins was confirmed in several regions of Canada between 2019-2022.
  • ECB damage on Cry1Ab, Cry1A.105 and Cry2Ab2 Bt corn was confirmed in Connecticut in 2023-2025.

The players

Fei Yang

University of Minnesota Extension corn entomologist.

Yucheng Wang

University of Minnesota Department of Entomology, Postdoc Researcher.

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What they’re saying

“Timely resistance monitoring is important for detecting and managing potentially resistant ECB. Early detection provides valuable information that is needed to devise appropriate management strategies for resistant insects.”

— Fei Yang, University of Minnesota Extension corn entomologist

What’s next

To determine if ECB is developing resistance in your area, we recommend scouting and collecting ECB larvae or eggs for Bt toxin bioassays. If you observe any ECB infestation in your corn fields, please contact Fei Yang ([email protected]). We are interested in checking the damage, testing the Bt expression, and collecting insects for testing their survival on Bt proteins.

The takeaway

The discovery of ECB feeding on Bt corn plants in Minnesota highlights the need for ongoing monitoring and resistance management strategies to ensure the long-term viability of this important pest control technology for the state's corn growers.