Effects of dietary conditioning on feeding behavior on cotton ofHeliothis zea(Boddie) third and fifth instars were examined in a greenhouse study. Larvae were conditioned from hatching to third or fifth instars on field-grown cotton flower buds or an artificial wheat-germ diet. Larvae reared on flower buds fed more, rested less, and locomoted less than larvae reared on the artificial diet. Bud-fed larvae generally preferred feeding on flower buds, whereas larvae reared on the artificial diet preferred feeding on blooms. These data show that feeding responses of later instars on a single cotton cultivar are dependent on dietary conditioning, and that dietary conditioning can affect results of studies involving bollworm feeding behavior.