In insect olfactory receptor neurons, rapid and transient increases in inositol triphosphate (IP₃) and Ca²⁺ are detected upon stimulation with pheromone or nonpheromonal odorants. This suggests that heterotrimeric guanine nucleotide binding proteins (G proteins) may transduce some odorant responses in insects. We obtained cDNA clones encoding three classes of G protein α subunits, Bm G_o, Bm G_q, and Bm G_s, from the antennae of the adult male silkmoth (Bombyx mori). RT‐PCR experiments showed that the mRNA of these G protein α subunits was also present in the various tissues of adult and larval insects. We used immunocytochemistry to localize these G protein α subunits in adult male and female antennae. In the adult male antennae, anti‐G_o antiserum stained the nerve bundles. In contrast, anti‐G_q and anti‐G_s antisera stained the inner and outer dendritic segments of the putative olfactory receptor neuron. The localizations of Bm G_o, Bm G_q, and Bm G_s in the female antennae were the same as in the male antennae. The localizations of Bm G_q and Bm G_s suggest that each subunit mediates a subset of the odorant response. J. Comp. Neurol. 485:143–152, 2005. © 2005 Wiley‐Liss, Inc.