Potential field evolved resistance of European corn borer to Bt traits in Connecticut

In the early 1900s, the European corn borer (Ostrinia nubilalis; ECB) was introduced to North America near Boston, MA. By 1942, ECB was distributed throughout the major corn-growing regions of North America and was the most economically impactful corn-insect pest through the 20th century. Many management strategies were attempted, but few were successful until 1996 with the commercialization of genetically modified corn encoded with Bacillus thuringiensis (Bt corn).

Bt corn has been highly effective at controlling ECB. Over 20 years, no cases of ECB resistance to targeted toxins were identified; however, in 2018, evidence of resistance to Cry1F was reported in Nova Scotia and continues to persist. In 2023, as a part of a general Bt resistance monitoring project, sweet corn expressing Cry1Ab, Cry1A.105, and Cry2Ab2 and non-Bt sweet corn were planted and monitored in Connecticut. Within these plots, the first occurrence of live ECB larvae and their tunneling injury in plants expressing Cry-A corn were observed in the United States. Of the 200 non-Bt plants that were surveyed, 25% had ECB injury/tunnelling and 55 live larvae were found. Of the 300 Bt plants that were surveyed, 23% had ECB injury/tunnelling and 30 live larvae were found. The extensive tunneling and presence of larvae in Bt corn at rates comparable to non-Bt corn provides evidence of potential ECB resistance to Cry-A traits. In 2024, the sampling effort was expanded to quantify prevalence or extent of ECB resistance in Connecticut.