Planting milkweeds and other wildflowers is essential to support monarch butterfly population growth. A recently published journal article focusing on new monarch habitat placement provides an overview of 20 Iowa State University research studies. Photo by Jacqueline Pohl. (larger image)
AMES, Iowa – When the Iowa Monarch Conservation Consortium was formed seven years ago, Iowa State University researchers faced two big questions about restoring milkweed and other wildflowers necessary for the survival of the iconic butterfly: how can the habitat be restored and where should it be located?
The “how to” of restoring habitat is described in the Consortium’s Prairie Planting Guidelines. “Where” is the subject of a new peer-reviewed journal article that provides an overview of 20 ISU studies as well as the work of other monarch researchers. The paper, published in Bioscience earlier this month, synthesizes years of research including field observations, laboratory experiments and simulation modeling. The findings are largely optimistic.
Mobility helps
The researchers found that establishing new habitat at the rates called for in Iowa’s conservation plan would increase monarch population size by 10 to 25 percent per generation, depending on different use scenarios. pesticides and the amount and location of habitat creation.
“Basically, we’ve concluded that planting habitat anywhere you can in the agricultural landscapes of the Upper Midwest will support the growth of monarch breeding generations, even if some of that habitat is near fields of crop treated with insecticides,” said Professor Steven Bradbury. of Ecology and Natural Resource Management at Iowa State.
The highest range of estimated population growth assumes using integrated pest management practices and applying insecticides only when pests can cause economically significant crop damage, Bradbury said.
Establishing habitat adjacent to crop fields where insecticides are used is expected to produce more monarchs than if prairie restoration is limited to sites away from the fields. A 100- to 125-foot buffer between treated fields and habitat patches would eliminate swathes of conserveable land, Bradbury said, for example, up to 80 percent of available non-crop land in Story County. Giving up that much space would make it difficult to add the 1.3-1.6 billion new milkweed stems needed in the Upper Midwest to support a sustainable monarch population.
Insecticide spray drift from treated crops can pose risks to monarch caterpillars, which live exclusively on morning glory plants. However, the impact on the general population is mitigated because females are highly mobile within their summer breeding grounds, Bradbury said.
“The females move a lot around the landscape. They don’t put all their eggs in one basket,” he said.
While some monarchs downwind of treated fields may have high mortality rates, other eggs are laid in areas of habitat that are not exposed to the insecticides, Bradbury said. And milkweed plants near treated fields can still support the next generation of adults.
Using radio transmitters to track female monarchs gave researchers better insight into their non-migratory flight patterns. Monarchs ride wind currents to travel up to tens of miles a day as they migrate to and from the mountainous oyamel fir forests in Mexico, where they spend the winter. But breeding females also fly between habitat areas when they’re not migrating, in flights that can exceed a mile, the researchers found.
“They don’t migrate when they take these big flight steps, but they seem to activate migration-like behavior,” Bradbury said. “The general idea was that breeding females moved a lot to lay their eggs, but there had been no empirical study quantifying their non-migratory movement patterns.”
This mobility is part of the reason modeling shows that monarch numbers will still increase if the added habitat is fragmented. However, research suggests that new habitat plots of at least 6.2 acres located in close proximity, 160 to 330 feet apart, will provide the most support.
what lies ahead
Research and outreach is ongoing for the consortium, a diverse partnership of more than 45 organizations that includes the state of Iowa, the Iowa Department of Agriculture and Land Stewardship, the Iowa Department of Natural Resources Iowa, federal agencies, agriculture and conservation associations, and agri-food and utility companies. . But now is a good time to summarize the group’s research because it has reached a natural point to gather the best information available, Bradbury said.
“Sometimes in a novel there are a series of chapters that are part of the first part. Our analogy is that we have reached the end of the first part,” he said.
There’s also a practical consideration, he said. The U.S. Fish and Wildlife Service will reconsider in 2024 whether the monarch should be protected under the Endangered Species Act, and fact-finding for the decision will likely begin in 2023. It’s time ideal for sharing an overview of new research on the monarch.
Future tasks for the researchers include collecting additional field data on spawning patterns and integrating ISU’s regional modeling with continental-scale models to predict how restored habitat in the Upper Midwest will affect the size of the wintering population in Mexico.
The research methods used by the Iowa State team could also be replicated in other areas where summer-breeding monarchs reside. Although about half of the population that migrates to Mexico comes from the Upper Midwest, other breeding destinations for monarchs, such as New England and southern Ontario, have different climates and landscapes.
Interdisciplinary and multi-layered research doesn’t just benefit monarchs. Bradbury said it has offered numerous opportunities for undergraduate and graduate students to work on projects with a wide variety of stakeholders.
“This is a strength for a researcher. Working with landowners can help refine research questions and ensure results that help advance useful conservation practices,” he said.
The collaborative nature of the consortium also serves as a model for the coexistence of conservation and agricultural production in Iowa, Bradbury said.
“Conserving the monarch is common ground that brings people together, and these are relationships we can use to address other challenges we face,” he said.
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