Widespread annual occurrence of pesticides within designated Critical Habitats for Endangered prairie butterflies

Abstract

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. We do not understand the extent of that exposure risk, particularly across seasons and multi-year timeframes. Over nine years, we analyzed grass and soil samples for the presence of hundreds of pesticides from five prairies in Minnesota and South Dakota that are designated as Critical Habitat for two endangered butterflies: Poweshiek skipperling and Dakota skipper. We found 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 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. Few pesticides were detected in soil or early season grass samples. The risk associated with the prevalence and quantities of pesticides we observed likely underestimates the overall risk. Implications for Conservation: Our work demonstrates protected prairies are not immune to the risk of pesticide exposure, and that this may impact planned efforts to re-establish lost populations of imperiled prairie insect species, including endangered butterflies.