The morphology and distribution of sensilla on the antennal flagella of male and female adults of Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae), were investigated by using scanning and transmission electron microscopy (SEM and TEM). Behavioral responses of male and female adults were measured with 12 host-plant and leaf-volatile stimuli. No sexual dimorphism was observed in the distribution and types of sensilla. Two types of sensilla, trichodea and basiconica, were observed on the antennae. Sensilla trichodea were distributed on all antennal segments but were most abundant on the last 3 segments. In contrast, sensilla basiconica were found exclusively on the last 3 segments of the antenna. TEM cross sections showed sensilla trichodea to have a thick cuticular wall and regular point-shaped pores around the cuticular wall. Sensilla basiconica possessed a thin wall and continuous pores and dendrites. The pores on the walls of the sensilla indicate that they play a role in sensing chemical stimuli and in olfactory functions. Female and male adults of T. castaneum showed broad overlap in their behavioral responses to various odors. Preference for some volatiles was noted, but after removal of the 3 terminal antennal segments, there was no significant preference for any compound that had been previously attractive to the beetles when tested with the complete antennae.