Unusual response characteristics of pheromone-specific olfactory receptor neurons in the Asian corn borer moth, Ostrinia furnacalis

Male moth pheromone-detecting receptor neurons are known to be highly specific and very sensitive. We investigated physiological and behavioral responses to female sex pheromone components in male Ostrinia furnacalis moths (Lepidoptera: Crambidae). Using recordings from a cut-sensillum technique, trichoid sensilla could be grouped into four physiological types (1-4), according to the response of receptor neurons to the two major pheromone components, (E)-12- and (Z)-12-tetradecenyl acetate (E12- and Z12-14: OAc). These types could subsequently be characterized as four subtypes (A-D) depending on neural responses to pheromone components from various sister species of O. furnacalis, (Z)-9-, (E)-11- and (Z)-11- tetradecenyl acetate. The peripheral pheromone detection system of O. furnacalis is different to that of other moths. A large majority of the neurons investigated responded to both of the two principal pheromone components. Dose-response and cross-adaptation studies showed that olfactory receptor neurons with large amplitude action potentials responded equally well to E12- and Z12-14: OAc in sensillum types 1-3. Field experiments showed that O. furnacalis males are sensitive to ratios of E12- and Z12-14: OAc and that (Z)-9- tetradecenyl acetate acts as a behavioral antagonist. O. furnacalis males thus display an unusual coding system for odors involved in sexual communication, mainly built on less specific neurons, but still have the ability to detect and respond to the correct female blend. We hypothesize that the pheromone detection system of O. furnacalis consists of two parts, where one is devoted to high sensitivity to Delta 12 isomers of tetradecenyl acetate, E12- and Z12-14: OAc and the other to highly specific responses to the E12- or Z12-14: OAc. The unusual feature is thus that a large part of the system is devoted to sensitivity and only a minor part to selectivity. This could be explained by the fact that no other moth species are known to use E12- and/or Z12-14: OAc and that no strong selective pressure to increase selectivity between the isomers has been determined.