LANSING, Mich. (Michigan News Source) — Insecticides, particularly neonicotinoid-treated seeds, have emerged as the primary culprit behind the decline in butterfly populations and species diversity across the Midwest, a new study from Michigan State University reveals. In particular, the study shows an 8% reduction in butterfly species diversity—a long-term effect of these agricultural chemicals.

The MSU research team, led by ecologist Nick Haddad, analyzed 17 years of data from 81 counties spanning five states. They examined agricultural practices, including the use of herbicides and insecticides, and their impact on butterfly populations. The study is groundbreaking, as it is the first to evaluate the long-term effects of various pesticides—especially those attached to plants through coated seeds—on butterfly diversity, according to MLive.

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“As the best-known insect group, butterflies are key indicators of broader insect decline, and the implications of our findings for conservation will extend to the entire insect world,” said Haddad told Mlive.

The study’s comprehensive approach revealed that insecticides, rather than herbicides, were primarily linked to the decline in monarch butterfly populations, a species of particular concern in recent years.

Ashley Cole-Wick, a wild butterfly expert with the Michigan Natural Features Inventory, explained the complexity of the issue.

“It’s almost impossible for a farmer to find corn seed that isn’t coated, pre-coated in insecticides like neonicotinoids,” Cole-Wick said, as reported by Mlive. 

Insecticides, particularly neonicotinoids, disrupt the nervous systems of insects, leading to paralysis and death. These chemicals are often applied as seed coatings, and while they are intended to protect crops from pests, they can leach into the soil and water, affecting non-target species like butterflies. 

While neonicotinoids were initially seen as a breakthrough in the 1990s for targeting specific pests with minimal harm to humans and animals, their persistence in the environment has led to unintended consequences, including the decline of beneficial insects like butterflies and bees.

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Moreover, the loss of habitat due to agricultural expansion and urban development reduces the availability of nectar sources and breeding grounds for butterflies. 

Despite the grim findings, efforts are underway to mitigate the impact of insecticides on butterfly populations. 

Laurie Juday, known as the “butterfly lady” of Northern Michigan, has been actively involved in raising and releasing monarch butterflies, according to MLive. She encourages gardeners to create “waystations”—gardens that provide milkweed, nectar sources, and water—to support butterfly populations.