John Pleasants: Solutions for loss of Monarch butterfly populations

Picture by: Kim Smith
Picture by: Kim Smith


I would like to expand upon Dennis Keeney’s fine column of Sept. 21 on the plight of the monarch butterfly.

I have worked on these butterflies for 15 years, and Mr. Keeney cites my research in his article. He notes that the population crashed in 2012 and 2013 because of bad weather, but by that time, the population had already declined by 65 percent since 1999.

Our data show that this decline was primarily due to the loss of milkweeds in the Midwest, the primary breeding area for monarchs.

Between 1999 and 2012, almost 99 percent of milkweeds in Midwest agricultural fields disappeared due to the use of Roundup herbicide (glyphosate) in conjunction with Roundup Ready corn and soybeans.

I have estimated that this amounts to a loss of more than 700 million milkweed plants. In addition, the conversion of grassland and CRP (Conservation Reserve Program) land to cropland in recent years has increased the total number of milkweeds lost to about 1 billion.

This constitutes a 64 percent decline in milkweeds in the Midwest.

The number of milkweeds sets an upper limit on the size of the monarch population; weather can determine if this limit is reached.

Because of the loss of milkweeds only a small population can now be supported.

This makes the population more vulnerable to weather events like those in the breeding range in 2012 and 2013 and on the overwintering site in Mexico in 2002 when a winter storm killed 500 million butterflies, 75 percent of the population (for comparison, last year’s overwintering population totaled only 33 million).

There are solutions. Clearly, we have to plant milkweed to replace some portion of those that were lost.

The two habitats that have the most potential for milkweed augmentation are roadsides and CRP land, which together harbor the majority of milkweeds that remain today.

To increase milkweeds in roadsides we can ramp up the ongoing efforts by programs such as the IRVM (Integrated Roadside Vegetation Management) to plant native vegetation along roadsides.

Roadside managers could also be made aware of the negative impact that spraying and mowing roadsides have on milkweeds and monarchs. CRP land is an especially promising habitat for milkweed augmentation; there are 5 million acres of CRP land in the Midwest suitable for milkweed.

Farmers are compensated for setting this land aside from crop production but must plant cover species to prevent erosion.

Milkweed seed could easily be added to the seed mix used for this purpose.

There already exist special CRP programs that involve creating pollinator-supportive habitat.

These could be expanded. To induce farmers to add milkweed to their CRP land we need financial incentives and readily available milkweed seed and propagation expertise.

I am currently working with fellow biologists, representatives of the farming community, industry and federal agencies on these initiatives.

I want to also recognize the contribution of individuals who plant milkweed in their yards.

If we are successful in all of these efforts we may be able to marvel for years to come on the migration of monarch butterflies.

John M. Pleasants is an adjunct assistant professor in the Department of Ecology, Evolution and Organismal Biology at Iowa State University.


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