The red flour beetle, Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae), is a worldwide pest of stored grains. Using “Y”-tube olfactometry we studied the response of T. castaneum to odors from simulated wheat infestations containing conspecifics, and infestations containing the lesser grain borer, Rhyzopertha dominica (F.) (Coleoptera: Bostrichidae), and the granary weevil Sitophilus granarius (L.) (Coleoptera: Curculionidae). Tribolium castaneum larvae were significantly attracted to odors from all three test species. Tribolium castaneum adults were attracted to grains infested by R. dominica and flour infested by T. castaneum but repelled from grains infested by S. granarius. Further behavioral analysis with pheromones showed that T. castaneum were significantly attracted to their aggregation pheromone, dimethyldecanal (DMD), but not to the R. dominica aggregation pheromone, a mixture of dominicalure 1 and 2. Female T. castaneum adults were attracted to ∼50-fold less DMD than larvae and 100-fold less than male adults, suggesting they are more sensitive to DMD. This study improves our understanding of T. castaneum behaviors to infested grain volatile compounds and pheromones, and may help develop new control methods for grain pest species.