Scientists find migrating monarch butterflies benefit from bract milkweed

Newswise — ITHACA, N.Y. – Researchers at Cornell University have identified a species of milkweed that holds promise for planting on roadsides to improve conservation habitat for migrating monarch butterflies.

Scientists surveyed the poorly studied bract milkweed to document where it grows, which organisms make use of the plant, seed production, and concentrations of toxins. The study’s findings verify that the species is a good candidate for planting within roadside or rights-of-way conservation projects.

Entomologists have been alarmed by a global drop in insect numbers. Migrating monarchs have not been spared, with loss of habitat and host plants – such as milkweeds for larvae to grow along migratory routes – as potential reasons for the drop in monarch numbers.  

As a result, some management projects are replacing invasive grasses previously planted along roadsides and pipelines with native species that feed and provide habitat to insects.

“With over 130 species of milkweed in North America, we are just beginning to understand the biology of the majority of species, which are typically rare or more restricted in their range than the common milkweed, which dominates the Northeast,” said Anurag Agrawal, professor of environmental studies at Cornell and the paper’s senior author.

For the study, researchers drove and walked 3,000 miles along pipelines and roadsides within the Chihuahuan Desert in North America and adjoining ecoregions to survey and locate bract milkweed populations.

Due to the timing of the surveys, they did not find monarchs on the plants, but Agrawal has done studies to show that monarchs feed and develop successfully on bract milkweed.

Bract milkweed flowers have nectar that supports pollinators, including native bee species, blue and gossamer-winged butterflies, and predatory insects that help control crop pests.

Milkweed’s toxins can cause illness or even kill livestock, so ranchers often remove it from their lands and oppose planting it near their fields. The researchers found that bract milkweed contains high levels of toxins in the wild, yet it only spreads into disturbed and mowed areas.

“During the surveys, I kept finding it on roadsides and the population stretched along disturbed areas, but they did not at any point ever cross fence lines into undisturbed or less managed areas,” said postdoctoral researcher Shaun McCoshum. “That’s an exciting aspect of this milkweed for roadside restoration purposes, especially for concerned landowners.”   

Seed companies may now use this information to produce seeds targeted for areas within the plant’s range to establish it for conservation purposes and to prevent soil erosion.

For additional information, see this Cornell Chronicle story.

Cornell University has dedicated television and audio studios available for media interviews supporting full HD, ISDN and web-based platforms.

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