I examined the impact of Tetraopes tetraophthalmus (Forster) on its host plant, Asclepias syriaca L., through a series of field observations and experiments. Adult beetles feed on milkweed flowers and foliage while larval beetles feed on the rhizomes of milkweed. Strong negative effects of beetle herbivory on milkweed growth, but not sexual reproduction, were found in experiments comparing growth for milkweed patches from which adult beetles were removed to controls with an unmanipulated abundance of beetles. Experiments using potted milkweed revealed a strong negative effect of beetle larvae on the growth of milkweed roots and rhizomes. Under natural field conditions, I could detect no effect of adult beetle density on the growth or sexual reproduction of milkweed. Overall, it appears that below ground herbivory by beetle larvae negatively impacts milkweed growth, but detection of these effects under natural conditions are confounded with a number of factors.