Insecticide use is the single largest factor contributing to a decline in total butterfly abundance and species diversity in the Midwest, according to a newly released study published by the journal PLOS ONE from Michigan State University.

This study builds upon research performed by Braeden Van Deynze with Scott Swinton, a University Distinguished Professor in the Department of Agricultural, Food and Resource Economics. Van Deynze earned his doctorate from MSU in 2019 and is currently a natural resource economist for the Washington Department of Fish and Wildlife.

“What drives butterfly decline is a hard nut to crack, due to rapid changes in chemical and genetic technologies alongside changes in climate and butterfly habitat,” says Swinton. “Our team was able to link 17 years of farm-level data on crops and inputs with detailed county-level data on butterfly abundance by species. This research is the first to evaluate the long-term effects on butterflies of herbicides, sprayed insecticides and systemic insecticides, while controlling for climate and land use change.”

While habitat loss, climate change and pesticides have all been implicated as potential causes for the declining insect abundances being observed globally, this work was the first comprehensive long-term study to evaluate their relative effects. Using 17 years of land use, climate, multiple classes of pesticides and butterfly survey data across 81 counties in five states, the researchers found that shifts in insecticide use toward neonicotinoid-treated seeds are associated with an 8% decline in butterfly species diversity across the American Midwest.

These findings include the decline of the migratory monarch butterfly, which has been a prominent concern. Specifically, it is noted that insecticides rather than herbicides are the strongest pesticide factor associated with monarch declines.

This research is particularly impactful as butterflies play an essential role in pollination and serve as key markers of environmental health. Understanding the primary factors contributing to their decline will help researchers working to protect these species, benefiting our environment and the sustainability of food systems.

“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 ecologist Nick Haddad from the MSU W.K. Kellogg Biological Station and the Department of Integrative Biology.

The paper notes the complexity of these many contributing factors and how difficult they can be to separate and measure in the field. The study calls for more publicly available, reliable, comprehensive and consistently reported pesticide use data, particularly for neonicotinoid seed treatments, to fully understand the drivers of butterfly decline.

In addition to Van Deynze, Swinton and Haddad, co-authors for this paper include David Hennessy from Iowa State University and Leslie Ries from Georgetown University.

Read the full paper on PLOS ONE.