Tucson Standard

A recent study published in the Proceedings of the National Academy of Sciences has uncovered a new genetic basis for resistance to transgenic crops in one of the United States' most significant crop pests, the corn earworm. Researchers from the University of Arizona's Department of Entomology have identified that field-evolved resistance in this pest is not linked to any of the 20 genes previously associated with resistance to pest-killing proteins found in genetically engineered crops.

Bruce Tabashnik, head of the Department of Entomology and senior author of the study, stated, "The corn earworm is one of the world's most challenging pests in terms of its ability to quickly evolve resistance in the field to genetically engineered crops. We identified 20 genes that harbor mutations conferring resistance to pest-killing proteins based on previous work with lab-selected strains of corn earworm as well as resistant field populations and lab strains of other lepidopteran pests." He added, "We call these 20 genes 'the usual suspects.' Contrary to our expectations, in seeking the culprit for field-evolved resistance of corn earworm, none of the usual suspects were guilty."

The research highlights that Bt crops, which produce proteins from Bacillus thuringiensis bacteria, are widely used due to their efficacy and safety. However, pests like the corn earworm have developed resistance over time. In 2024, Bt varieties accounted for a significant portion of U.S. corn and cotton planting.

Luciano Matzkin, a professor at U of A and co-author, explained that bioassays were used routinely at Texas A&M University to test insect resistance by exposing them to Bt proteins. The collaboration allowed researchers to perform genomic analyses on insects preserved from these bioassays.

Andrew Legan, a postdoctoral fellow at U of A and first author of the study noted, "We carefully examined 20 genes that affected how pests responded to Bt proteins in previous studies. Our evidence indicates changes in these genes are not causing resistance to Bt crops in wild populations of the corn earworm." He continued by saying that instead they found "resistance was associated with a cluster of genes that was duplicated in some resistant field populations."

This discovery underscores how genetic bases for resistance can vary between laboratory conditions and real-world scenarios. It also emphasizes how genomic analyses can complement bioassay results for monitoring pest resistance effectively.