A sex pheromone isomer modulates pheromone receptor sensitivity in Bombyx mori

Bombykol, (E,Z)-10,12-hexadecadien-1-ol, is a sole sex pheromone component essential for mating in the silkmoth Bombyx mori. The bombykol isomer EE-kol is consistently present across all silkmoth strains tested, but its role in sex pheromone communication remains unclear. Previous studies have indicated that BmOR1 is involved in EE-kol detection. Here, we reevaluated the function using the Xenopus oocyte expression system and two-electrode voltage clamp recording method. EE-kol elicited inward currents in BmOR1-expressing oocytes only at very high concentrations and with a markedly smaller response than to bombykol. EE-kol co-application reduced the bombykol-induced currents in a dose-dependent manner at higher bombykol concentrations, whereas plant-derived alcohols did not cause significant suppression. At the antennal level, EE-kol evoked a weaker response than bombykol, and the bombykol-EE-kol mixture shifted the dose-response curve rightward, with little change in the maximal response. These results support the conclusion that EE-kol acts as a partial agonist of BmOR1 and competitively suppresses the bombykol-induced response. These findings raise the possibility that a well-conserved pheromone isomer may modulate sex pheromone receptor sensitivity in the silkmoth.