In a growing challenge to crop protection efforts, the corn earworm, one of the most notorious pests in U.S. agriculture, is showing signs of building resistance to genetically engineered crops. A new study published in the Proceedings of the National Academy of Sciences highlights the alarming speed at which this pest is adapting, making it increasingly difficult to control and threatening the effectiveness of biotechnological advancements in farming.
Genetic Engineering to Combat Crop Pests
In an effort to reduce pesticide use and protect crops from destructive pests, genetic engineering has become a key tool for farmers. One of the most significant innovations has been the development of transgenic crops that produce bacterial proteins known as Cry proteins, which are toxic to specific insect pests like the corn earworm (also known as Helicoverpa zea or the cotton bollworm). These proteins are designed to kill the pests while posing no harm to humans, animals, or beneficial insects.
The idea behind genetically engineered crops is straightforward: by introducing a bacterial gene into the plant’s DNA, the plant can produce a protein that disrupts the pest’s digestive system, effectively killing it without the need for chemical insecticides. Over the years, this technology has been adopted widely, with crops such as cotton, corn, and soybeans being engineered to produce Cry proteins to combat pest infestations.
However, despite the benefits of these innovations, there has been growing concern about pests developing resistance to the proteins produced by transgenic crops. As crops genetically modified to resist pests have become more widespread, some pests are adapting to overcome the defenses, reducing the efficacy of these biotechnological solutions.
The Study: Uncovering a New Genetic Resistance
The recent study conducted by researchers from the University of Arizona’s Department of Entomology sheds light on the genetic basis of resistance in the corn earworm, a major pest of U.S. corn and cotton crops. For years, scientists have identified a set of genes, known as “the usual suspects,” that were linked to resistance in laboratory strains of the corn earworm and other related pests. These genes had been implicated in enabling pests to resist Cry proteins, providing the foundation for ongoing research into pest control strategies.
However, this new study reveals that field-evolved resistance to transgenic crops in the corn earworm is not tied to any of the 20 genes previously associated with resistance. This unexpected discovery challenges long-held assumptions about how pests are evolving in response to genetic engineering and opens new avenues for understanding the genetic mechanisms at play.
Bruce Tabashnik, the senior author of the study and head of the Department of Entomology at the University of Arizona, explained the significance of the findings. “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,” he said. “While we had previously identified 20 genes that were believed to harbor mutations conferring resistance, none of these ‘usual suspects’ were found to be the culprits in the field populations we examined.”
Uncovering Resistance: The Role of Genomics
To understand the genetic basis for the corn earworm’s resistance, the University of Arizona team collaborated with researchers at Texas A&M University. The Texas A&M team had conducted bioassays to evaluate resistance in field-derived corn earworms. These insects were collected from various sites across the southern United States and tested for their ability to survive on transgenic crops that produced Cry proteins.
Once the bioassays were completed, the researchers at Texas A&M froze the insects and sent them to the University of Arizona for further analysis. The University of Arizona team performed DNA extractions and sequencing to scan the entire genome of the corn earworm caterpillars. By comparing the genetic makeup of resistant and susceptible populations, they hoped to identify the genetic differences responsible for the pests’ increasing resistance.
The genomic analysis included a total of 937 corn earworms sampled from 17 different locations across seven states in the southern U.S. These specimens were collected over an 18-year period, from 2002 to 2020. The extensive sample size and long-term data collection allowed the researchers to track how resistance had evolved over time and pinpoint the genetic changes that contributed to the corn earworm’s adaptation.
Unexpected Findings: No Link to Known Resistance Genes
The results of the genomic analysis were surprising. Contrary to the team’s expectations, none of the 20 genes previously identified as “usual suspects” in laboratory studies showed a link to the field-evolved resistance observed in these corn earworms. This indicates that the mechanisms driving resistance in real-world populations are likely more complex than previously thought.
“The corn earworm is demonstrating an ability to evolve resistance in the field at a faster pace than we can fully understand,” said Tabashnik. “The results from this study indicate that we need to think beyond the established set of genes and explore new possibilities for how resistance might be developing.”
The researchers are now focused on identifying other genetic factors that might be contributing to resistance. This will likely involve more in-depth genomic analyses to identify potential mutations and new genes involved in the adaptation process. Understanding the full genetic landscape of resistance will be key to developing more effective strategies for managing pests like the corn earworm in the future.
The Growing Challenge of Pest Resistance
The rapid evolution of resistance in pests like the corn earworm highlights the ongoing challenges faced by farmers who rely on genetically engineered crops to control pest populations. While transgenic crops have undoubtedly reduced the need for chemical insecticides and improved crop yields, the resistance problem underscores the need for more sustainable and integrated pest management approaches.
As pests like the corn earworm evolve resistance, it becomes increasingly important to implement strategies that combine genetic engineering with other control methods, such as crop rotation, natural predators, and the use of chemical insecticides in a more targeted and sustainable manner. The goal is to reduce the selective pressure on pests and slow down the development of resistance over time.
“We’re not saying that genetically engineered crops are the problem,” said Tabashnik. “They are a valuable tool in pest management. But they need to be part of a broader, integrated strategy that includes other approaches to minimize the risk of resistance.”
A Call for Continued Research and Innovation
The findings of this study serve as a reminder of the complexity of pest resistance and the need for ongoing research to stay ahead of evolving threats. As agricultural practices continue to evolve, so too must the strategies used to combat pests. The corn earworm is just one example of how quickly pests can adapt, and it underscores the importance of investing in new technologies, strategies, and approaches to ensure the long-term viability of transgenic crops and other crop protection methods.
The researchers at the University of Arizona are continuing their work to unravel the genetic underpinnings of resistance in the corn earworm and other pests. Their goal is to provide farmers with better tools to manage pest populations and ensure food security in the face of rapidly evolving challenges.
Conclusion: The Future of Crop Protection
As the resistance of pests like the corn earworm continues to grow, it is clear that the battle between biotechnology and nature is far from over. The findings from the University of Arizona’s study offer valuable insights into the genetic factors driving resistance and serve as a call to action for further research and innovation in the field of crop protection.
While genetically engineered crops remain a critical tool in modern agriculture, the need for integrated pest management strategies that combine genetic, chemical, and ecological approaches has never been more pressing. By staying vigilant and proactive, scientists and farmers can work together to ensure that crop protection efforts remain effective in the face of evolving resistance.
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