Monarch butterflies have no choice in the matter: their existence is completely dependent on milkweed. And in recent years, the decline of milkweed in fields and gardens has brought a correlated decline in the monarch population.
But researchers behind a new joint project between the David Suzuki Foundation and the University of Guelph hope to restore the plant and create a safe-haven corridor in southern Ontario for the migratory insect.
"If we don't have milkweed, we don't have monarchs," said Tyler Flockhart, a postdoctoral researcher at the University of Guelph. Milkweed is the only plant the butterfly eats and the only plant on which it will lay eggs, Flockhart explained in an interview with Craig Norris on The Morning Edition.
Flockhart identifies two main causes for the plant's decline. The first is "changes in biotechnology: the use of genetically-modified corn and soybean that removes milkweed very efficiently from those crops. The other is urban development, which removes the natural plants and replaces them with concrete and gardens that are comprised largely of ornamental plants."
"It's also a toxic plant," he added, "and a really aggressive grower. And that's why it's come into conflict with farmers. Livestock will eat it and it will reduce crop yields, so that's why it's been targeted for a long time to remove it from agricultural fields."
The decline in milkweed has dramatically reduced the number of butterflies, Flockhart said. So the first step is to "get more milkweed into the ground, really, really quickly."
According to Flockhart, the easiest way to do this is to plant milkweed on land currently reserved for special purposes.
He said the project aims to create "linear corridors" by planting milkweed along roadsides, power line towers and pipeline pathways. The challenge, he said, is that these areas have been managed a certain way—clear-cutting and reducing native plants—for a very long time.
Monarchs are not the only ones who would benefit from milkweed corridors. Flockhart said other pollinators, such as hummingbirds, bees and wasps, also enjoy milkweed. These insects and birds are really important in food production and biodiversity, he added, "and these populations are in mass decline. It's quite alarming."
Flockhart envisions expanding the program to include other native flowering plants in the same areas, to benefit other pollinating insects.
The second step, he said, is to encourage home gardeners to plant milkweed instead of ornamental plants. "It smells good," he said, "and it attracts a huge number of butterflies and bees."
"It's important this fall when you're out at your local nursery—it's important to say to them you want to have milkweed in the spring," he said, so that they'll order the seeds and have them in stock for the planting season.
In 2014, the Ontario government removed milkweed from its "noxious plant" list, which meant public gardeners and private industry were no longer compelled to remove it on sight or forbidden from planting it. The change in classification was meant to address concerns over the decline of the monarch butterfly population and to encourage biodiversity with indigenous plants.
In 2014, Henry Denotter, an oilseeds farmer and then-president of the Ontario Soil and Crop Improvement Association supported the move. He observed that if farmers had a crop-related issue with the plant they were permitted to remove it from fields but were encouraged to leave it along fence lines and rough areas.