Larvae of the buckeye butterfly, Junonia coenia (Nymphalidae) feed primarily on plants in four families: Scrophulariaceae, Plantaginaceae, Verbenaceae, and Acanthaceae. These families have in common the secondary compounds, iridoid glycosides. Growth and survival on the artificial diet with iridoid glycosides was comparable to that on plants. Choice tests using artificial diets showed that larvae: chose diets with iridoid glycosides over a diet without; showed no preference between the crude extract and pure iridoid glycoside; and preferred the diet with ground leaves of the host plant, Plantago lanceolata , over the diet with pure iridoid glycosides. The artificial diet that larvae had been reared on prior to these tests had no effect on subsequent larval preferences in the choice tests.