Abstract
The remarkable responsiveness of male moths to female released pheromones is based on the extremely sensitive and selective reaction of highly specialized sensory cells in the male antennae. These cells are supposed to be equipped with male-specific receptors for pheromonal compounds, however, the nature of these receptors is still elusive. By using a combination of genomic sequence analysis and cDNA-library screening, we have cloned various cDNAs of the tobacco budworm Heliothis virescens encoding candidate olfactory receptors. A comparison of all identified receptor types not only highlighted their overall high degree of sequence diversity but also led to the identification of a small group of receptors sharing >40% identity. In RT-PCR analysis it was found that distinct members of this group were expressed exclusively in the antennae of male moths. In situ hybridization experiments revealed that the male-specific expression of these receptor types was confined to antennal cells located beneath sensillar hair structures (sensilla triochoidea), which have been shown to contain pheromone-sensitive neurons. Moreover, two-color double in situ-hybridization approaches uncovered that cells expressing one of these receptor types were surrounded by cells expressing pheromone-binding proteins, as expected for a pheromone-sensitive sensillum. These findings suggest that receptors like Heliothis receptor 14-16 (HR14-HR16) may render antennal cells responsive to pheromones.