The feeding behavior ofPlodia interpunctella(Hübner) larvae was analyzed by using separate bioassays for stimuli eliciting short-range orientation responses and for stimuli involved in the maintenance of feeding. Nonpolar and polar extracts of wheat, corn (maize), and peanuts elicited both orientation and feeding responses in this polyphagous insect. When the role of carbohydrates in larval feeding behavior was studied, sucrose, fructose, glucose, maltose, fucose, and melibiose were powerful feeding stimulants. Also, tests with combinations of active and inactive sugars demonstrated that the total concentration of sugar directly influenced larval feeding. Thus, behaviorally inactive sugars could affect feeding behavior positively in a synergistic manner or by increasing the total concentration. Amino acids had little effect on feeding, even when used in combination with sucrose. Fatty acids and sterols had no effect by themselves, but when linoleic, oleic, and palmitic acids were used in combination with subthreshold levels of sucrose, a definite synergistic feeding effect occurred.