Pheromonal activities of the bombykol isomer, (10E,12E)-10,12-hexadecadien-1-ol, in the pheromone gland of the silkmoth Bombyx mori.

Bombykol (EZ) is the single component of the female sex pheromone in the silkmoth Bombyx mori. EZ alone evokes full courtship behaviors from conspecific males; however, its geometric isomer (EE) was consistently detected in the pheromone glands (PG) of 16 B. mori strains and a field population of the wild silkmoth Bombyx mandarina, which also uses EZ as the single pheromone component. We investigated the pheromonal activities of EE using a commercial hybrid strain of B. mori, Kinshu × Showa. The behavioral assay demonstrated that a 10-10-fold higher dose of EE than EZ was able to elicit behavioral responses from males. To elucidate whether the trace contaminant of EZ in the EE standard is responsible for these responses, we examined the responses of male antennae to EE using a gas chromatograph-electroantennographic detector system (GC-EAD). The EE, at high doses elicited marginal responses from the male antennae. We next examined antennal and behavioral responses of B. mori whose BmOR1 gene, which is responsible for the reception of bombykol, was knocked out. The knockout of BmOR1 resulted in the complete loss of antennal and behavioral responses to EE and EZ, demonstrating that if EE itself is active, it induces these responses via the incidental stimulation of BmOR1, not via the stimulation of EE-specific receptors. The existence of EE in the PG of B. mori and B. mandarina is discussed from the viewpoints of pheromone biosynthesis and the evolution of pheromone communication systems.