Two species of nymphalid butterflies, the monarch (Danaus plexippus), and painted lady (Vanessa cardui), were exposed to plants treated with 1X and 2X soil applications of Marathon (1% imidacloprid). Residue analysis quantified the presence of imidacloprid in nectar of a single flower: 3 ppb in controls, 29 ppb in 1X, and 54 ppb in 2X plants. Adult survivorship or fecundity was not reduced, but larval survivorship was reduced on imidacloprid-treated Asclepias curassavica. It is important to understand if greenhouse grown plants that are treated with imidacloprid for pests contain residues that affect foraging adult butterflies and caterpillars.