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An in-depth examination of data spanning over a decade and involving ten states in the U.S. Corn Belt reveals that economic challenges face farmers due to the excessive use of genetically modified corn engineered to address rootworm infestations.
The analysis, spearheaded by Christian Krupke, an entomologist at Purdue University, highlighted increased rootworm pest prevalence particularly in western Corn Belt states, including Illinois, Iowa, Minnesota, Nebraska, North Dakota, South Dakota, and Wisconsin, where continuous corn planting is a common practice. In contrast, farmers in eastern Corn Belt states like Indiana, Michigan, and Ohio engage in crop rotation, which decreases reliance on genetically modified seeds or insecticides. Despite these regional differences, the employment of transgenic corn hybrids aimed at combating rootworms has been relatively uniform throughout the entire Corn Belt, prompting this study to investigate the resulting implications.
Krupke, who is a Dean’s Fellow and professor of entomology, collaborated with 19 co-authors from various universities across the U.S., China, and Canada to publish their findings in the prestigious journal Science. The retrospective analysis reveals a significant shift in the pest management landscape across many essential corn-growing regions in the U.S. since 2004, the year when transgenic corn hybrids initially gained widespread adoption targeting corn rootworms. The findings indicate that pest pressures notably decreased in extensive areas following the introduction of these hybrids, which diminished the necessity for broad use of rootworm-specific traits.
“This study underscores the importance of long-term, applied research datasets sourced from public sector fieldwork,” remarked Krupke. He pointed out that the limited duration and ever-changing focus of research funding make it increasingly rare to access such comprehensive biological data. “These datasets are invaluable for informing policy decisions,” he stated.
The first genetically engineered corn hybrid with a trait fatal to corn rootworms, derived from the bacterium Bacillus thuringiensis (Bt), was launched in 2003, leading to widespread adoption of these “Bt corn” hybrids by farmers. Research conducted in the years since has reported the emergence of Bt-resistant rootworms beginning in 2009, casting uncertainty on the longevity of the Bt traits.
The study arose from the insights gathered by a group of corn entomologists who convene annually to evaluate pest impacts on corn production. Krupke observed a divergence in pest reports for corn rootworms between eastern and western regions of the Corn Belt.
“Though we each operated in different areas of the country, we employed similar management strategies,” Krupke explained. “Despite the shifting dynamics, we continued to treat the pest with Bt hybrids as if rootworm damage was a significant factor affecting yields in states like Indiana, which had not been accurate for some time.”
The research indicated that between 2014 and 2016, yield losses attributed to rootworm damage amounted to an average of 47.5 bushels per acre in the western states but dropped to 8.5 bushels per acre in the eastern regions.
The analysis assessed two primary costs associated with using Bt hybrids: the significant technology fee that farmers must pay for the seed, and the diminishing susceptibility of pests to the Bt toxin.
“Visualize a Bt hybrid as a declining resource, akin to a debit card; with each application, you chip away at the susceptibility,” Krupke noted. “This means it becomes less effective with each use.”
Farmers frequently choose superior hybrid seed genetics to optimize their yields, which often come bundled with a range of desirable traits, including various Bt toxins, regardless of necessity.
Christina DiFonzo, a field crops entomologist at Michigan State University, likened the bundling of seed traits to the past offerings from cable TV. Consumers used to pay for a multitude of channels, but only wished for a select few. The evolution of streaming services has altered that paradigm. “Farmers would certainly appreciate a similar ‘pick list’ for seed options that would bolster insect resistance management,” she proposed.
However, the challenge with insect-resistant corn is the ongoing collateral cost incurred alongside direct monetary expenses. “While financial resources can be replenished, the loss of pest susceptibility to the technology is an irreversible process,” DiFonzo cautioned.
Such insights should inform the development of future transgenic technologies for in-plant protection, advised the study’s lead author, Ziwei Ye, an assistant professor at Renmin University of China’s School of Agricultural Economics and Rural Development. She cautioned against reverting to traditional insecticides, such as organophosphates and pyrethroids, for rootworm management.
“The BT technology has provided significant benefits, contributing to the protection of beneficial organisms and soil ecosystems while also enhancing drought resilience,” Ye emphasized. “These attributes are increasingly recognized as essential in meeting the food demands of an expanding global population in the face of climate change.”
Both Bt and antibiotics exemplify the concept of the “biological commons.” Farmers may see value in using them as a protective measure, even when pest threats seem limited. However, widespread long-term usage can lead to resistance, ultimately undermining the technology’s effectiveness for everyone.
“While using Bt may appear beneficial to individual farmers, it accelerates the technology’s decline for all,” noted study co-author David Hennessy, the Cargill Professor in Economic Systems at Iowa State University. “Most individuals fail to consider the cumulative harm caused to others through the development of resistance to the toxin.”
Consequently, many farmers have tended to overutilize Bt seeds aimed at rootworms for their financial gain, particularly in the eastern Corn Belt.
“In numerous instances, they overapply this input not only for individual advantage but also at the expense of broader agricultural health,” Hennessy observed. Encouraging farmers to weigh the financial implications of using the rootworm Bt trait more critically could contribute to preserving the technology’s efficacy.
Looking ahead, Krupke affirmed that the adoption of transgenic technologies like Bt maize as key pest management tools is likely to persist, owing to their ease of use for farmers and the reduction in insecticide application they facilitate.
“Maintaining the functionality and existence of this and similar technologies for the long term is in everyone’s best interest,” he concluded.
This research received support from the State Agricultural Experiment Station (SAES) through the Hatch Multistate Research Fund, provided by the National Institute for Food and Agriculture (NIFA Project NC246: Ecology and Management of Arthropods in Corn), as well as the National Natural Science Foundation of China.
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