Corn–toxin blend found to produce more aerodynamic pest moths

A new study from North Carolina State University indicates that corn earworm pests can develop more aerodynamic, long-distance-flight wing shapes after feeding on a blend of genetically modified Bt corn and non-Bt corn. The findings raise concerns that seed blends designed to help manage resistance may, in some cases, facilitate the spread of resistance traits across cropping regions.

Researchers found that caterpillars consuming a mixed diet of toxin-producing and non-toxic corn developed moth wings that were longer, narrower and more tapered—resembling the profile of a fighter aircraft. According to the team, these wing characteristics increased stiffness and improved the insects’ ability to remain airborne in higher wind speeds.

“Insects eating a blended toxic and non-toxic corn diet were stiffer and more able to travel in higher wind speeds,” said Dominic Reisig, professor and extension specialist of entomology at NC State and co-corresponding author of the study. “These insects are able to get up into the winds and ride them longer distances.”

The study compared moths raised on four diets: pure non-Bt corn, pure Bt corn with two toxins, pure Bt corn with three toxins, and a seed blend of 80% three-toxin Bt corn and 20% non-Bt corn. Moths raised on the blended diet showed the most aerodynamic wing changes—and did so within a single generation. By contrast, insects raised on any of the three unblended diets developed less aerodynamic, more brittle wings.

Corn earworm (Helicoverpa zea) is a widespread pest in North America. While corn crop losses are generally manageable, the species also damages soybean, tomato and cotton, making its movement and resistance patterns a significant concern for farmers across multiple sectors. Because earworms emerge in high numbers from cornfields in midsummer, any shift in their flight capability directly affects how rapidly resistance traits can disperse into other crops and regions.

“It appears that resistance occurs faster when worms eat these blends, creating individual moths that have multiple resistance mutations,” Reisig said. “This is one more piece of evidence that blending Bt and non-toxic corn pollen is really dangerous for resistance.”

The research, published November 19 in Environmental Entomology, used geometric morphometric analysis and finite element modeling to assess wing structure and performance under simulated wind conditions. The authors report that the blended-diet moths exhibited wing shapes most conducive to long-distance dispersal.

The study adds to ongoing scientific debate over seed-blend refuge strategies, which mix Bt and non-Bt seed in a single bag. While blends are intended to simplify refuge compliance, some researchers argue that they may accelerate resistance development in certain pest species.

The work was supported by a Biotechnology Risk Assessment Grant from the US Department of Agriculture’s National Institute of Food and Agriculture and by the University Global Partnership Network.

Researchers say further work is under way to assess additional biological effects, including mating success, in earworm populations exposed to mixed corn diets.