Warmer temperatures make milkweed toxic for monarchs


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A monarch caterpillar scoots across a common milkweed leaf. (USFWSmidwest/flickr)

Jenna Ladd | April 6, 2018

A recent study published in the journal Ecology uncovered an unexpected consequence of climate change for monarch butterflies.

Researchers from Louisiana State University and University of Michigan set out to understand how warmer temperatures affect the relationship between monarch butterflies and milkweed plants. The insects, whose population has declined by more than 80 percent in the last decade, lay their eggs exclusively on milkweed plants. After the larvae hatch, they feed on certain species of milkweed, which provide protection to the butterflies. Milkweed plants produce chemicals called cardenolides in their leaf tissues, which are poisonous to most of the monarch’s predators. When monarchs consume the perfect amount of these chemicals as larvae, it sends a signal to larger predators to stay away from them.

However, scientists found that as regional temperatures rise, some species of milkweed plants produce more cardenolides. This poses a threat to the monarchs’ survival. One of the researchers, Dr. Bret Elderd, an associate professor at Louisiana State University, explained, “It’s a Goldilocks situation for monarch butterflies. Too few of these chemicals in the milkweed, and the plant won’t protect monarch caterpillars from being eating. But too high of a concentration of these chemicals can also hurt the monarchs, slowing caterpillar development and decreasing survival.”

One species of milkweed by the Latin name of A. curassavica has naturally high levels of cardenolides in its leaves and is especially sensitive to rising temperatures. Landscapers and environmentalists alike have been planting more of the nonnative plant to save the monarchs, but scientists warn that this plan may have backfired. They are working to spread the word that the native variety of milkweed, A. incarnata, has naturally lower levels of cardeolides and is much less likely to become toxic to monarchs as the climate warms.

The study reads, “It has become increasingly recognized that species interactions, especially interactions between tightly-linked species, need to be considered when trying to understand the full impacts of climate change on ecological dynamics.”

The full report can be found here.

Group hopes to use RAGBRAI to restore Iowa’s Monarch populations


Nick Fetty | July 23, 2015

The Register’s Annual Great Bike Ride Across Iowa (RAGBRAI) kicked off this week and one CGRER member is hoping to use the event as a opportunity restore Monarch butterfly populations in the Hawkeye State.

CGRER founding member David Osterberg and University of Iowa College of Public Health research support specialist Nancy Wyland organized an event last week inviting people to help make milkweed  “seed bombs.” These bombs consist of soil, compost, and milkweed seeds rolled into a ball – roughly the size of a golf ball – which will be distributed to RAGBRAI riders as they make their way through Mount Vernon Friday afternoon.

Riders are encouraged to toss these seed bombs in ditches along roads in Linn and Johnson County to bring back milkweed plants with the hope of restoring Iowa’s Monarch butterfly population. Estimates show a 90 percent decline in Monarch populations over the past 20 years.

Osterberg and his group helped create roughly 600 seed bombs as part of a larger effort spearheaded by Monarchs in Eastern Iowa, a group that aims to store Monarch populations in Eastern Iowa. Last year the group raised and released approximately 1400 butterflies.

Among the riders participating in this effort is Kelly “Milkweed” Guilbeau. The Grinnell resident, who sports a butterfly costume during the ride, first began tossing out seed bombs last year. Guilbeau also manages a blog which focuses on Monarch butterflies.

This year marks the 43rd anniversary of RAGBRAI with approximately 20,000 participants on this year’s ride.

On the Radio: Genetically modified crops affect monarch butterfly populations


Photo by Dave Govoni, Flickr.

Listen to this week’s radio segment here or read the transcript below. This week’s episode discusses the effects genetically modified crops on monarch butterflies.

Monarch butterfly populations are declining.  Some research suggests that genetically modified crops may be partially responsible.

This is the Iowa Environmental Focus.

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