Single-cell electrophysiological recordings were obtained from olfactory receptor neurons in sensilla trichodea on male antennae of the heliothine species Heliothis subflexa and the closely related congener H. virescens. A large percentage of sensilla (72% and 81%, respectively, of all sensilla sampled) contained a single odor-responsive receptor neuron tuned to the major pheromone component of both species, Z-11-hexadecenal. A second population of sensilla on H. subflexa antennae (18%) housed receptor neurons that were tuned to Z-9-hexadecenal but also responded with less sensitivity to Z-9-tetradecenal. A similar population of sensilla (4%) on H. virescens male antennae housed receptor neurons that were shown to be tuned specifically only to Z-9-tetradecenal, with no response to even high dosages of Z-9-hexadecenal. A third population of sensilla (comprising 8% and 16% of the sensilla sampled in H. subflexa and H. virescens, respectively) housed two olfactory receptor neurons, one of which was tuned to Z-11-hexadecenyl acetate and the other tuned to Z-11-hexadecenol. In H. subflexa the Z-11-hexadecenyl acetate-tuned neuron also responded to Z-9-tetradecenal with nearly equivalent sensitivity. The behavioral requirements of males of these two species for distinct pheromonal blends was, therefore, reflected by the subtle differences in the tuning properties of antennal olfactory receptor neurons.

Abstract. In genetic studies on the sex pheromone communication system of two races of European corn borer, which use opposite pheromone blends of the E and Z compounds, it was found that antennal olfactory cell response amplitudes to the two compounds were controlled by an autosomal factor, whereas behavioral responses to the blends were controlled by a sex-linked locus. Because of the difference in genetic controls, it was postulated that some unusual males would be produced in F2 crosses between these two races. These unusual males would have antennal olfactory cells that respond as the Z-race males, but would respond behaviorally to the E blend. The present studies combined behavioral studies in a flight tunnel and single cell electrophysiological studies to show that these unusual males do indeed exist. These findings show that the spike amplitude of peripheral olfactory cells is not important in regulating species-or race-specific pheromone responses, as compared to some central nervous system factor assesses the spike frequencies from different pheromone-component-specific cells on the antenna. This factor seems to be essential in governing the pheromone-blend specific behavioral responses of male moths.

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We used single sensillum recordings to define male Helicoverpa zea olfactory receptor neuron physiology followed by cobalt staining to trace the axons to destination glomeruli of the antennal lobe. Receptor neurons in type A sensilla that respond to the major pheromone component, (Z)-11-hexadecenal, projected axons to the cumulus of the macroglomerular complex (MGC). In approximately 40% of these sensilla a second receptor neuron was stained that projected consistently to a specific glomerulus residing in a previously unrecognized glomerular complex with six other glomeruli stationed immediately posterior to the MGC. Cobalt staining corroborated by calcium imaging showed that receptor neurons in type C sensilla sensitive to (Z)-9-hexadecenal projected to the dorsomedial posterior glomerulus of the MGC, whereas the co-compartmentalized antagonist-sensitive neurons projected to the dorsomedial anterior glomerulus. We also discovered that the olfactory receptor neurons in type B sensilla exhibit the same axonal projections as those in type C sensilla. Thus, it seems that type B sensilla are anatomically type C with regard to the projection destinations of the two receptor neurons, but physiologically one of the receptor neurons is now unresponsive to everything except (Z)-9-tetradecenal, and the other responds to none of the pheromone-related odorants tested.