Sex pheromone investigations of the domesticated silkmoth, Bombyx mori (Lepidoptera: Bombycidae), helped elucidate the molecular and physiological fundamentals of chemical communication in moths, yet little is known about pheromone evolution in bombycid species. Therefore, we reexamined the sex pheromone communication in the wild silkmoth, Bombyx mandarina, which is considered ancestral to B. mori. Our investigations revealed that (a) B. mandarina females produce (E,Z)-10,12-hexadecadienol (bombykol), but not (E,Z)-10,12-hexadecadienal (bombykal) or (E,Z)-10,12-hexadecadienyl acetate (bombykyl acetate), which are pheromone components in other bombycid moths; (b) antennae of male B. mandarina respond strongly to bombykol as well as to bombykal and bombykyl acetate; and (c) bombykal and bombykyl acetate strongly inhibit attraction of B. mandarina males to bombykol in the field. The present study clarifies the evolution of pheromone communication in bombycid moths.