Widespread annual occurrence of pesticides within designated critical habitats for endangered prairie butterflies

Abstract

Insect declines have become pronounced in prairie ecosystems, particularly in areas of agricultural intensification. Non-target pesticide exposure has been raised as a key concern for prairie remnant health. Over seven years, we screened grass and soil samples for the presence and quantities of hundreds of pesticides from five prairies in Minnesota and South Dakota that are designated as Critical Habitat for two globally endangered butterflies: Poweshiek skipperling and Dakota skipper. We documented dozens of pesticides across all sites and years on their larval host grasses. Interiors of prairies were not less likely to have detectable pesticides than along prairie-agriculture edges. Broad-spectrum organophosphate and pyrethroid insecticides were common in late season. Chlorpyrifos quantities were higher at sites where both endangered species have been extirpated. Neonicotinoid insecticides, which have been frequently attributed to declines in insect pollinators, did not present a significant exposure signal in these prairie habitats. Few pesticides were detected in soil or early season grass samples. The prevalence and quantities of pesticides we observed are likely underestimates, and additional research is needed on the landscape of risk at small and large scales. Implications for Conservation: Protected prairies are not immune to the risk of pesticide exposure, which may impact efforts to re-establish lost populations of imperiled prairie insects, including endangered butterflies.