Milkweed, only food source for monarch caterpillars, ubiquitously contaminated

New evidence identifies 64 pesticide residues in milkweed, the main food for monarch butterflies in the west. Milkweed samples from all of the locations studied in California’s Central Valley were contaminated with pesticides, sometimes at levels harmful to monarchs and other insects. 32% of the samples contained pesticide levels known to be lethal to monarchs, according to a study released today in Frontiers in Ecology and Evolution.