Missing All the Monarch Butterflies?

They face a new pesticide threat on the horizon

Monarch butterfly on showy milkweed. (Credit: Tom Koerner/USFWS. (CC BY 2.0))

Reprint of op-ed in The Kansas City Star

As a kid growing up in Leawood, Kansas in the 1990s it was hard to imagine a day when the annual migration of monarchs across the Great Plains might disappear forever.

Some summer days it seemed like the orange and black butterflies were everywhere, darting through the steamy midday air and fluttering around my mom’s milkweed-bordered rose garden like oversized confetti.

These days when I return every summer to visit family and friends, I rarely see any monarchs.

So for me, it hit home when Mexican officials announced on March 5 that the number of overwintering monarchs had dropped by an estimated 14 percent from last year. That’s bad news for a butterfly population that has declined by 80 percent in just two decades.

The ongoing decline foreshadows an ever-darkening picture for monarchs heading into a growing season where farmers are projected to use tens of millions of additional pounds of the drift-prone pesticide dicamba. In 2017 alone, dicamba sprayed on crops genetically altered to resist it spurred thousands of reports of drift damage to more than 3 million acres of nearby crops and untold stretches of forests and natural areas.

And based on pesticide-makers’ own projections, the potential for dicamba damage is about to increase 100-fold as U.S. farmers ramp up use of dicamba over the next two years across 60 million acres — an area larger than Minnesota.

The projected explosion in dicamba use is troubling for monarchs because the pesticide is very toxic to milkweed, the only food of the monarch caterpillar.

As described in an analysis I released earlier this month, peer-reviewed research shows that just 1 percent of the minimum recommended dicamba application rate can drastically reduce the size of milkweed and severely wither the leaves the caterpillars need to survive.

Dicamba may even cause greater harm to milkweed than the pesticide glyphosate, which has played a significant role in reducing milkweed across the heart of the monarch’s annual migratory path.

Worse yet, as demonstrated by an interactive mapping tool on the Center for Biological Diversity’s website, the timing and geographical distribution of dicamba use coincides precisely with the presence of monarch eggs and larva on milkweed.

Dicamba also harms other flowering plants that provide nectar for adult butterflies as they travel south back to Mexico for the winter.

Monarch populations have already lost an estimated 165 million acres of breeding habitat across the United States to herbicide spraying and development. Yet when the Environmental Protection Agency approved new dicamba products in 2016, it did not even analyze risks to monarchs.

Although pesticide companies insist their new dicamba products are less prone to drifting, research by independent scientists at several universities indicates the new products are just as drift-prone as older formulations. To limit off-target damage from dicamba several states, including Missouri, have set seasonal deadlines after which the weed-killer cannot be sprayed.

Dicamba use on crops genetically engineered to withstand it was supposed to be the solution to the development of glyphosate-resistant superweeds across millions of U.S. acres.

Now, recent surveys make clear the false hope of the nation’s pesticide dependence: Some weeds are already evolving resistance to dicamba.

By the time glyphosate’s harm to monarchs was discovered, the pesticide was already firmly entrenched. With dicamba we have a unique opportunity to limit the worst damage before it happens.

But that will require that those who care about the future of monarchs and the environment let the EPA know it should refuse to re-approve dicamba in November.

Otherwise, we risk making the monarch a dark symbol of our failure to acknowledge the unacceptable costs of continuing to dump hundreds of millions of pounds of pesticides across the U.S. every year.

Kansas native Nathan Donley is a former cancer researcher who is now a senior scientist at the Center for Biological Diversity.