Monarch caterpillar performance (leaf mass consumed, caterpillar mass, and consumption efficiency (caterpillar mass/leaf mass consumed) on milkweed leaf discs painted with fungicide doses (ppb).

In controlled trials we test the effects of two abundant residues (fungicides) on the growth and feeding of monarch butterfly caterpillars (which feed on milkweed host plants). In particular, we tested the hypothesis that exposure to pesticides may be most impactful on poor quality host plants.