The monarch butterfly — an orange and black icon that is Minnesota's state insect — is facing dire population declines that have resulted in the smallest wintertime habitat since surveys began in 1993, an international team of conservation scientists warned Wednesday.

Monarch butterflies migrate nearly 2,500 miles from Minnesota and southern Canada to central Mexico, where they spend the winter — the second-longest migration of all known insects.

But in recent years, severe weather changes resulting from global warming, deforestation from illegal logging in Mexico and natural enemies of the butterfly have resulted in periodic population declines.

This year, conservationists say the area where the butterflies winter in Mexico was reduced by 44 percent, to just 1.7 acres.

Karen Oberhauser, a University of Minnesota entomologist who's spent 30 years studying the butterflies, says the expansion of genetically modified crops in the Corn Belt is the primary culprit behind precipitous monarch declines over the past three years. These crops allow farmers to use herbicides later in the growth cycle, which has led to vast reductions in native milkweed and nectar plants that the butterflies rely on during the breeding cycle.

The monarch's decline may be an indicator of larger ecological problems, she said.

"What is happening to monarchs is also happening to many other uncounted organisms — organisms whose loss would be equally tragic," Oberhauser said.

There is considerable overlap, for example, in the habitats of monarchs and pollinators like bees, she said. The monarchs provide an easy way for scientists to study population changes because they gather in discrete locations every winter, "and because thousands of volunteers count them," Oberhauser said.

The latest results from the annual monarch survey were released Wednesday at a news conference in Mexico organized by the World Wildlife Fund and Telcel, the leading provider of wireless phones in Mexico.

It's uncertain how low the migrating monarch population can go before it suffers a fatal collapse.

"We're never going to recover what we had because we've lost too much habitat," Oberhauser said. "And the habitat that's been lost to GM crops is never going to come back."

But she estimated that migratory monarchs in North America would be sustainable if conservation efforts could restore their spring and summer breeding grounds to the point where their wintertime habitat would occupy between 7.5 and 10 acres.

Phil Schappert, an ecologist in Halifax, Nova Scotia, who's written extensively about monarch butterflies, credited Mexico with great strides in the past several decades to protect the butterflies.

"It is past time for Canada and the United States to enact measures to protect the breeding range of the monarch, or the spiral of decline will continue," he said in prepared remarks.

Conservation efforts

On Wednesday, the participating scientists called on public officials in Canada, the United States and Mexico to cooperate on conservation efforts and develop an action plan when they meet Feb. 19 in Mexico for the North American Leaders' Summit.

Most of the questions at Wednesday's news conference focused on events in the United States, Oberhauser said. For decades the focus has been Mexico's conservation efforts, partly because the butterflies nest in 11 relatively small, well-defined preserves. Their huge range in the United States makes conservation efforts difficult.

U.S. farmers grow corn that has been engineered to be toxic to lepidoptera, a moth called the European corn borer. Pollen from this corn is toxic, and conservationists fear that it may blow onto milkweed plants that monarch butterflies rely on. Corn also has been engineered to resist herbicides like Roundup, which kills milkweed.

Oberhauser said monarchs can adapt to disturbed habitats as long as milkweed and nectar plants are present. She said a number of state and federal agencies, universities and nongovernmental organizations are working together in what's called the Monarch Joint Venture to replace lost habitats. Individuals can help, she said, by planting locally sourced, native milkweed and nectar plants, and by spreading the word. It's important to use local plants, she said, because some varieties, especially those planted year-round in some southern states, have led to disturbances in the migratory patterns.

Individuals also can help by asking property managers and local governments to avoid mowing milkweed plants when monarch eggs and caterpillars might be present, and by avoiding the use of insecticides.

Monarch butterflies are also found in California, Hawaii, Australia, New Zealand and southern Spain and Portugal, among other places. So the butterfly is not threatened with extinction, Oberhauser said. "It's the migratory phenomenon" that's in jeopardy.

Dan Browning • 612-673-4493