Corn Earworm Building Up More Resistance To Crop Protection Efforts

To minimize damage and reduce the need for insecticide sprays, crops have been genetically engineered to produce bacterial proteins that kill key pests but are not harmful to people or wildlife. However, widespread planting of such transgenic crops has led to rapid adaptation by some pests. A new study in the Proceedings of the National Academy of Sciences reveals a novel genetic basis of resistance to transgenic crops in one of the most important crop pests in the U.S. — the corn earworm.

Researchers from the University of Arizona Department of Entomology in the College of Agriculture, Life and Environmental Sciences used genomics to investigate the genetic changes causing resistance to transgenic crops in field populations of the corn earworm, also known as cotton bollworm or Helicoverpa zea. They discovered that in this pest, field-evolved resistance was not associated with any of the 20 genes previously implicated in resistance to the pest-killing proteins in transgenic crops.

“The corn earworm is one the world’s most challenging pests in terms of its ability to quickly evolve resistance in the field to genetically engineered crops,” says senior study author Bruce Tabashnik, head of the Department of Entomology. “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. 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.”

To analyze the genetic basis of field-evolved resistance of corn earworm, the U of A researchers collaborated with colleagues at Texas A&M University who had used bioassays to evaluate resistance by testing insects derived from the field. In this partnership, the insects from bioassays conducted at Texas A&M were frozen and sent to the U of A for DNA extraction and sequencing to enable scanning the entire genome for genetic differences between the resistant and susceptible corn earworm caterpillars. Including some previously sequenced specimens, the genomic analysis included 937 corn earworms from 17 sites in seven states across the southern U.S., sampled from 2002 to 2020.

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