Corn earworm (Helicoverpa zea) is a major pest of corn and other crops. In the past 20 years, as usage of Bt corn has risen, H. zea has steadily developed greater resistance to the insecticidal properties of the genetically modified corn, and a new study points to climate change as a factor accelerating the pest’s development of resistance. (Photo credit: Frank Peairs, Colorado State University, Bugwood.org)

Add “crop pests developing resistance to control methods faster” to the list concerning potential effects of global warming.

Entomologists at the Environmental Protection Agency (EPA) and the University of Maryland have collaborated on an analysis of two decades’ worth of agricultural and pest management data from the state of Maryland to explore the interplay of rising temperatures and increased usage of genetically modified corn. Their results, published this week in Royal Society Open Science, suggest that warmer temperatures can accelerate resistance development in pest insects.

Specifically, they analyzed the usage of Bt corn—which is engineered to contain a protein from the bacterium Bacillus thuringiensis that is toxic to many insects but harmless to humans—populations of corn earworm (Helicoverpa zea), and historical temperatures during growing seasons between 1996 and 2016. They found that higher-than-normal temperatures and high Bt corn acreage correlated with increases in damage to corn ears, kernel consumption of Bt corn, and the proportion of late instars of H. zea recorded.

“Broadly, our study highlights the challenges for pest management options, such as Bt biotechnology, in the context of climate change,” says P. Dilip Venugopal, Ph.D., science and technology policy fellow for the American Association for the Advancement of Science, currently hosted by the EPA, and co-author of the study. “The risk of Bt-resistant corn earworm spreading and its associated damages across many crops is high because, one, corn earworm overwintering range may expand further north from the present—40 degrees North latitude, around Maryland—due to climate change, and, two, the evolutionary selection pressure for resistance development exerted by extensive Bt acreage in Mid-Atlantic, North Central, and northern Great Plains regions.”

Venugopal and co-author Galen Dively, Ph.D., professor emeritus and integrated pest management consultant at the University of Maryland, emphasize that the relationship between temperature, Bt-corn usage, and the corn earworm’s development of resistance to Bt corn, is correlative, and the specific mechanics of the interactions are complex. However, they point to several possible factors at play. Higher temperatures, when coupled with high usage of Bt corn, may: degrade Bt proteins in crops; accelerate insect development, allowing H. zea to proceed through more generations each season; allow more H. zea to survive overwintering; and lead to northward expansion of resistant insects.

Roughly 80 percent of corn planted in the United States in recent years has been Bt corn, meaning measures to monitor and slow the development of resistance among corn pests is crucial—and the potential compounding effect of climate change only makes it more urgent.

“Corn earworm sampling for monitoring and testing for resistance is currently concentrated in the southern U.S. regions, where both Bt corn and Bt cotton are grown. We need expanded resistance monitoring in all high-corn production areas,” says Venugopal. The authors also emphasize the need to incorporate the evolutionary processes affected by climate change into resistance management programs.