Controversial pesticides threaten not just bees, but butterflies, too

Most of the furor surrounding neonicotinoids, the world’s most widely-used pesticides, focuses on the harms they cause to bees. Yet these chemicals may also pose a threat—presently little-appreciated but possibly grave—to butterflies.

In a study published in the journal Biology Letters, researchers led by biologist Matthew Forister of the University of Nevada tracked butterfly populations across four decades in three Northern California counties. Butterflies there face many challenges, including climate change, drought, and habitat loss to agriculture and urban sprawl. Yet even with those factors accounted for, neonicotinoids seem to pose a unique threat: the researchers found that declines in butterfly health and reproductive success accelerated dramatically after the pesticides entered widespread use in the mid-1990s.

There are caveats to the study, stress the researchers. “The evidence is correlational,” cautions study co-author Art Shapiro, an ecologist at the University of California, Davis, who started monitoring the region’s butterflies in 1972. “That’s not the same thing as proving causation.”

If not definitive, though, the findings do dovetail with similar results from a long-term, large-scale study of butterfly populations in Great Britain. They also fit with what’s known about the toxicity of neonicotinoids to insects and the chemicals’ ubiquitous environmental presence due to runoff from agricultural fields and urban landscaping. There might not be fire, but there’s certainly a lot of smoke.

Public concern about neonicotinoids and bees has prompted the Environmental Protection Agency to review their safety, and some municipalities have restricted their use. While awaiting further research and regulation, one wonders: what might become of a world with fewer butterflies?

“We don’t know,” says Shapiro. “For this area, at least, the sky has not fallen.” Then again, it’s only been an ecological eyeblink since the butterfly declines started. The effects may take many more decades to become obvious. Perhaps there would be fewer of the plants that butterflies pollinate, and fewer of the animals who feed on them. If nothing else, there would be a lot less beauty in the world. —Brandon Keim | 17 August 2016

Source: Forister et al. Increasing neonicotinoid use and the declining butterfly fauna of lowland California. Biology Letters, 2016. doi: 10.1098/rsbl.2016.0475

Image: A Mylitta crescent butterfly. Credit: Peter Pearsall/U.S. Fish and Wildlife Service