ISU research: Monarch butterflies may benefit from habitat near crops, despite risks

More monarch butterfly habitat may be added alongside crops in Iowa and across the nation, thanks to a yearslong Iowa State University research project.

North American monarch populations have declined between 80 percent and 99 percent over the last three decades, making the species a candidate for being protected under the federal Endangered Species Act. Threats to the butterflies include loss of habitat, changing weather conditions, insecticides and herbicides.

Iowa, along with much of the northern U.S., marks a summer getaway where monarchs come to breed. Their reproductive performance there is crucial to establishing the following year’s population. The Iowa Monarch Conservation Consortium aims to establish at least 788,000 acres of new habitat and at least 122 million milkweed plants — which monarch larvae depend on — by 2038 to help support populations.

“Iowa and neighboring states are in the bull's-eye, if you will, for the need for modern conservation,” said project lead Steve Bradbury, an ISU professor of natural resource ecology and management.

But how much new habitat is needed? And where do you put it?

Those are questions Bradbury’s multidisciplinary team of researchers pursued over seven years of research and incremental scientific articles, culminating in an overview article published this month in the peer-reviewed journal BioScience.

Since agricultural landscapes are so dominant in the Midwest, monarch habitat conservation hinges on its integration near fields and pastures. But those land uses are also accompanied by pesticides and herbicides — substances that can harm butterfly populations. The U.S. Department of Agriculture recommends limiting any new monarch habitat within 100 feet of treated crop fields.

That constraint severely limits the amount of land available for monarch habitats in the Midwest, which is home to more than 127 million acres of agricultural land. The ISU research team modeled that 38 percent of non-crop land cover and 84 percent of road rights of way in Story County, Iowa, would be ineligible for possible butterfly habitats by the USDA standards.

“That's a lot of space in the landscape that, in theory, couldn't be habitat establishments under the assumption that the pesticide exposure would seriously undercut conservation efforts,” Bradbury said. “But we're also realizing that blocking off that much of the landscape and not encouraging habitat establishment … could also undercut our conservation efforts.”

The ISU research team decided to study the trade-offs of weaving monarch habitat around agricultural lands using a combination of models, laboratory research and field observations. They recreated how monarchs move through landscapes; they investigated the impacts of dozens of chemical compounds; they simulated butterfly egg success rates. Altogether, the project was the first to assess how land use and pesticide use could influence monarch populations at a landscape scale.

The researchers found that some herbicides and pesticides of concern, like neonicotinoids, won’t severely harm nearby habitat patches through runoff. Monarch caterpillars can be impacted by spray drift, though, when applied chemicals waft in the air and move to different areas.

But that drift doesn’t impact all four directions at once — which creates possibilities for conservation, Bradbury said.

For instance, if a field was surrounded by monarch habitat and spray drift occurred, only one side could experience negative impacts. The other three could be relatively unscathed. On the other hand, if there was no habitat surrounding the field, there would be no monarchs benefiting.

“The big take home message was, ‘Get habitat in the ground anywhere you can, even if it's close to fields getting treated with pesticides,’” Bradbury said, noting that proper integrated pest management is important. “Even if those fields are getting treated every year — which would be unlikely — you’re still getting a higher production of monarchs than if you put those no-plant zones around the field.”

More findings, implications

The team uncovered more details about monarch ecology and behavior through the project.

Female monarchs are extremely mobile, flitting from place to place to lay her eggs. Using radio telemetry — a method using radio signals to measure distance — the researchers uncovered that monarch females periodically take large flights up to 1.5 miles. This marked the first empirical evidence of a widespread speculation, Bradbury said.

The scientists also deemed seven acres as the “sweet spot” for monarch habitat patch size, suggesting 160 feet to 300 feet between patches based on monarch flight routines. They also found that the butterflies tend to fly into the wind, potentially to sense smelling cues from plants upwind.

More research is needed to better understand how habitat patch characteristics correlate to butterfly success, Bradbury said. Additional research may also be needed as more herbicides, pesticides and fungicides are created and applied to fields.

Bradbury said he hopes his research goes beyond recovering the continental monarch population and aids efforts for increasing other biodiversity in agricultural landscapes. His team’s efforts could be replicated in other areas of the country with monarch populations.

The findings could also impact federal recommendations for monarch conservation. The U.S. Fish and Wildlife Service is scheduled to reevaluate the status of the monarch in 2024 to see if it should be placed on the federal Endangered Species List.

“It'll be interesting to see how the Fish and Wildlife Service, USDA and the Environmental Protection Agency use our information,” Bradbury said.

Brittney J. Miller is the Energy & Environment Reporter for The Gazette and a corps member with Report for America, a national service program that places journalists in local newsrooms to report on under-covered issues.

Comments: (319) 398-8370; brittney.miller@thegazette.com