Almost half the species of butterflies in the Midwest have declined in population in the last three decades, according to a recent study.
A Michigan State University Ph.D. candidate and her colleagues went through 31 years of data from butterfly counts in Michigan, Ohio, Indiana, Illinois, Iowa, and parts of Wisconsin, Minnesota, and Missouri.
Wendy Leuenberger is the lead author of a report published in the Proceedings of the National Academy of Sciences.
None of the butterfly species increased in population. Of the 136 species counted, 59 — more than 40% — declined in number.
Looking for butterflies in 1992 was a different experience compared to 2023 she noted.
Leuenberger said climate change and land-use are contributing factors. But there are also questions about a class of insecticides.
“We do think that there is more to look at with the pesticides.”
That’s because a class of insecticides called neonicotinoids started being used in the same timeline as the years studied.
Professor Elise Zipkin is director of MSU’s Ecology, Evolution, and Behavior Program and the senior author of the report.
She said some crop seeds are treated with neonicotinoids. “The seeds will be coated and then they’re put into the ground. And then it leaches into the soil so all other plants are affected,” said Zipkin.
The insecticides have also been linked to the decline in bees.
The U.S. Environmental Protection Agency has been looking at the concerns, but has not stopped the agricultural industry from using the neonicotinoids. It has made suggestions about ensuring the chemicals are used only on their intended targets.
Another factor specifically regarding the monarch butterfly decline is the eradication of milkweed on which it feeds.
The monarch butterfly has plummeted to 20 percent of what it was in the early 1990s. During the 1980s and onward, farmers cleared out fence rows, sprayed herbicides along ditches, or simply mowed them down in an attempt to get a few more acres into crop production. Much of the milkweed was lost.
Monarchs were also affected due to the use of genetically altered Bt corn. The corn pollen could get on the milkweed and the insecticide within the pollen could harm the butterflies.
