University of Arizona researchers discover surprising genetic causes of pest resistance in crops, challenging previous assumptions and highlighting new paths for managing agricultural pests.
In an unprecedented revelation, scientists have uncovered a novel genetic basis for resistance to genetically engineered crops in the corn earworm, one of the United States' most damaging agricultural pests. This breakthrough has significant implications for the management of biotech crops and the ongoing battle against pest resistance.
Crops genetically modified to produce pest-killing proteins, derived from the bacterium Bacillus thuringiensis (Bt), have long been heralded as a sustainable alternative to insecticides. These Bt crops are engineered to combat pests like the corn earworm (Helicoverpa zea), without harming humans or wildlife. However, the widespread adoption of Bt crops has led to rapid adaptation among pests, decreasing their effectiveness.
Researchers from the University of Arizona Department of Entomology embarked on a mission to identify the genetic changes behind field-evolved resistance in the corn earworm.
Prior studies had pinpointed 20 genes, labeled "the usual suspects," as responsible for resistance in lab-selected strains. To their surprise, these genes did not explain resistance in field populations.
"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," senior author Bruce Tabashnik, the head of the of the Department of Entomology at U of A, said in a news release. "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 uncover this mystery, U of A researchers partnered with Texas A&M University, utilizing bioassays to test corn earworm resistance.
"Bioassays are used routinely to determine if insects are resistant by exposing them to Bt proteins in the lab," co-author Luciano Matzkin, a professor of entomology at U of A, said in the news release.
Resistant and susceptible insects from these bioassays were genetically analyzed, including a substantial sample of 937 corn earworm specimens collected across 17 sites in seven southern states from 2002 to 2020.
"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," first author Andrew Legan, a postdoctoral fellow at U of A, added.
Instead, researchers found resistance linked to a duplicated cluster of genes, though the specifics of these genes' roles remain unclear.
Despite not pinpointing a single culprit, the findings underscore the complex nature of resistance and the need for integrated pest management strategies that consider both genetic and environmental factors.
Understanding the genetic factors behind resistance is crucial for developing effective monitoring tools and management strategies. By leveraging genomic analyses of resistant pests from routine bioassays, scientists aim to stay ahead in the ongoing battle against agricultural pests, ensuring the sustainability of biotech crops.
The study, set to be published on Nov. 8 in the Proceedings of the National Academy of Sciences, serves as "an important reminder that the genetic basis of resistance can differ between the field and lab," according to the researchers.
As agriculture faces evolving challenges, such discoveries pave the way for innovative and more sustainable pest management practices, safeguarding crop yields and reducing reliance on chemical insecticides.