Milkweed plants bought at nurseries may expose monarch caterpillars to harmful pesticide residues

The decline of monarch butterflies in both the eastern and western United States has garnered widespread public interest. Planting milkweeds, their larval host plants, been promoted as one action individuals can take, but little is known with respect to potential pesticide contamination store-bought milkweeds. In this study, we collected leaf samples from 235 milkweed plants purchased at 33 retail nurseries across US screen for pesticides. Across all samples, detected 61 different pesticides an average 12.2 (±5.0) compounds per plant. While only 9 these have experimentally tested on caterpillars, 38 % contained a above concentration shown sub-lethal effect monarchs. We modest predictive ability retailer size species; labels advertising value wildlife did not fewer concentrations negative These results demonstrate extensiveness exposure within nursery milkweeds impacts monarchs other insects exposed plants.