Monarch butterflies are a beloved species, and butterflies are important pollinators that help drive food production. But these vital species have been in decline for more than a century. Now, a new analysis shows that in recent years, the biggest factor in the decline of butterflies has been an unexpected insecticide, The New York Times reports.
What's happening?
The study specifically examined butterfly populations in the Midwest from 1998 to 2014. It tested many different variables, including six groups of pesticides, the world's rising temperature caused by air pollution, and changes in land use.
According to the Times, the study found that the top factor in butterfly declines over this 17-year period was the quick spread of insecticides called neonicotinoids. Originally created to deal with insects like aphids, this class of pesticides was introduced to the Midwest in 2003 and quickly adopted throughout the region. It caused a whopping 8% decline in butterfly populations compared to what they would have been without these pesticides.
"It's a story about unintended consequences," said study co-author Scott Swinton, a professor of agricultural economics at Michigan State University, according to the Times. "In developing technologies that were very effective at controlling soybean aphid and certain other agricultural pests, non-target species that we care about, butterflies in particular, have been harmed."
Why is this study important?
Neonicotinoids have been mostly banned in Europe since 2018 due to their impact on another group of pollinators: bees. Without pollinators, both natural environments and agriculture suffer. Pollinators carry pollen from one plant to another, fertilizing them and leading to the correct development of the fruits and seeds we rely on.
The study authors were clear that neonicotinoids weren't the only problem — just the one with the biggest impact during the study period, the Times reveals. Earlier, habitat loss had already taken a toll, and so had another pesticide: an herbicide called glyphosate, commonly known as Roundup, which kills the milkweed monarch butterflies need to survive. By the study period, that damage was already done.
The Times reports that Leslie Ries, another co-author and a professor of ecology at Georgetown University, thought more recent data might also tell a different story. "The last 10 years have been the hottest 10 years on record," she said. "So what is the impact in the last 10 years? We need to keep studying that, but it's hard to study it in total when we don't have neonicotinoid data."
What's being done about butterfly declines?
Data about the problem will help officials move forward with protective actions, like declaring monarch butterflies an endangered species.
Meanwhile, one company is releasing a system that will let farmers use less pesticide.
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