Monarch butterflies face bleak future, Iowa State University study finds

Monarch butterflies could face quasi-extinction in the next 20 years, according to Iowa State University researcher John Pleasants.

There is, he said, an 11 to 57 percent chance that the monarch population will fall so far that its migratory patterns will collapse.

'We're not saying it's going to zero, but to a level that it will be hard for them to recover from,” said Pleasants, an adjunct assistant professor of ecology, evolution and organismal biology at ISU.

Pleasants and colleagues reported that conclusion last month in a study by the U.S. Geological Survey and the Scripps Institution of Oceanography at the University of California, San Diego. It was published in the journal Scientific Reports.

The eastern migratory monarch population declined 84 percent between 1996 and 2014, according to Pleasants, who said a 2015 rebound caused by favorable weather in the breeding range had been partially offset by a winter storm March 8 and 9 at the winter colony in Mexico.

Pleasants said the 2015 rebound did not ease researchers' belief that the butterflies are in trouble.

'We need to significantly raise the milkweed ceiling for that to happen,” he said.

Weather and milkweed - the only plant on which the butterflies lay their eggs and the only plant their larva will eat - are the two main factors limiting monarch populations.

'We can't control the weather, so we have to put more milkweed on the landscape,” Pleasants said.

Widespread use of the herbicide glyphosate (most commonly applied as Monsanto's Roundup) has eliminated about 1 billion milkweed plants from North American crop fields - roughly half the milkweed available to the butterflies when their decline began 20 years ago, he said. (A Cedar Rapids consortium is also working to address the shortage of milkweed. Read about their story here: https://www.thegazette.com/news/consortium-tries-to-save-the-monarch-butterfly/)

This year's overwintering population in central Mexico covered about 10 acres, up dramatically from its low point of about 1.7 acres two winters earlier. From 1994 to 2006, butterfly coverage averaged 18.5 acres, but the average has shrunk to about 7 acres in the years since.

Pleasants said it would take about 2 billion additional milkweed plants on the landscape to support the 15-acre goal proclaimed in last year's national pollinator strategy. Doing so, he said, would cut the probability of quasi-extinction in half.

Pleasants said the study did not factor in increased milkweed levels. It factored weather patterns and natural variations in the monarch populations into the simulations and calculated the probability of the population sinking to levels that could lead to quasi-extinction.

'No one is saying we should go back to an era without Roundup. There is no way to go back,” Pleasants said.

That being the case, 'we need an all-hands-on-deck effort” to increase milkweed production on land other than crop fields, he said.

The two types of landscape holding the most promise, he said, are the nation's 24 million acres of Conservation Reserve Program grasslands and roadside ditches.

'Every little bit counts, including people growing milkweed in their lawns and gardens,” he said.

Doing so, he said, will enhance appreciation of the insect's perilous life cycle, in which only a few out of 100 monarch eggs ever become butterflies.

'It's hard being a butterfly. They need all the help they can get,” Pleasants said.