TOLUCA, MEXICO—Chalk one up for the lowly monarch butterfly.

It’s won some love in high places: at this week’s summit meeting of the leaders of Mexico, the United States and Canada.

The monarch, which has seen its numbers plunge in recent years, arose as a topic when Mexican President Enrique Pena Nieto hosted U.S. President Barack Obama and Prime Minister Stephen Harper for a meeting Wednesday to review the North American Free Trade Agreement, which created the world’s largest trade zone 20 years ago.

“We have agreed to conserve the monarch butterfly as an emblematic species of North America which unites our three countries,” Pena Nieto told business leaders who’d gathered for the one-day summit in the industrial city of Toluca, about 65 kilometres west of Mexico City.

In a final statement, amid weighty pronouncements on energy, immigration, border security and job creation, the monarch butterfly earned its place.

“Our governments will establish a working group to ensure the conservation of the monarch butterfly, a species that symbolizes our association,” the statement said.

The extraordinary 4,800-kilometre migration of tens of millions of monarch butterflies each year from the grasslands of Canada and the United States to the volcanic mountain slopes of central Mexico, where they completely cover fir trees, has awed human beings for centuries.

But the population of monarchs hibernating in Mexico from December to March has plummeted from a high of 1.1 billion in 1996 to a pitiful 33 million this year. That was enough to cover less than a hectare of forest in December, surveys show, down from 18 hectares two decades ago.

Experts once thought the drop was largely due to extreme climate conditions. But many now think there’s another factor: the butterfly is starving to death.

The relentless spraying of herbicides in North America is wiping out once-plentiful milkweed, the only plant that monarch caterpillars can eat. Small-scale illegal logging also is destroying the fir forest canopy in Mexico that the butterflies use as their wintering grounds.

More than 100 scientists, Nobel Prize winners and environmentalists had written to Pena Nieto, Harper and Obama before the summit, calling on them to establish a “milkweed corridor” through the three countries.

The petitioners called for the massive planting of milkweed along roadsides and toxin-free buffer zones in Canada and the United States.

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