It’s going to take the cooperation of three countries to ensure the survival of one butterfly species, and it needs to happen fast.

Declining for the past couple of decades, the monarch butterfly population fell to its lowest numbers this past winter since records started being kept in 1993. The main cause: loss of milkweed, its only source of food.

According to a new study led by Tyler Flockhart, a postdoctoral researcher at the University of Guelph, the spread of genetically-modified crops are an indirect killer.

Each autumn, monarch butterflies travel up to 4,000 kilometres from Eastern North America to Mexico, where they spend the winter hibernating in a small area of mountain fir trees. With its high rates of deforestation, this region has been the main focus for monarch conservation efforts thus far. However, this new report suggests redirecting the focus to America’s Corn Belt, an area in the Midwest, which has experienced the loss of about 1.5 billion milkweed plants due to genetically-modified crop planting, a farming practice that took off in the mid-nineties.

When genetically-modified crops with chemical resistance are planted, fields are doused in herbicides that get rid of any wild plants that grow in between rows, including milkweed. In the past, herbicides were applied early on in the season when milkweed seeds were still safely underground. But genetically-modified crop fields are sprayed later when the milkweed has vulnerably grown past the surface.

Other factors adding to the plant’s loss include reforestation in open areas where milkweed previously grew, urbanization and being listed in many jurisdictions as a noxious plant, leading to its removal because it’s poisonous to humans and grazing animals.

The study predicts that if the milkweed loss continues, monarch populations will fall another 14 per cent, leading to a five per cent chance of near-extinction over the next century.

One suggestion in counteracting this loss is delisting milkweed as a noxious plant in the United States. “It can be decided relatively quickly and it makes sense,” Flockhart says.

In Ontario, for example, milkweed was listed as a noxious plant for around 60 years, and all it took was a period of public consultation to change that this past May.

Planting milkweed on roadsides is another suggestion. These pieces of land are already held in the public trust, which would avoid private property issues and allow great conditions for the plants to grow. “They germinate better in disturbed soils,” Flockhart says.

Incorporating milkweed into city gardens can also be helpful. “Urban green roofs are popping up all over the place,” Flockhart says. “It’s the perfect opportunity.”

But those ideas would only replace the milkweed loss on an annual basis. Addressing the massive decline that has occurred the past few years requires a much larger, necessary discussion between Canada, the United States and Mexico.

“One of the neat things about migratory animals is that they require cooperation amongst different countries to make sure they persist,” Flockhart says.

The three leaders of these countries have all agreed on the importance of monarch conservation and indicated a plan needs to be made.

“It’s going to take all three in order to keep this migratory population viable.”