Olfactory receptor neurons specific to chiral sex pheromone components in male and female Anomala cuprea beetles (Coleoptera : Scarabaeidae)

Chemical communication in scarab beetles involves female-released long-dist ance sex pheromone. Electrophysiological recordings using tungsten microele ctrodes demonstrated two types of olfactory receptor neurons in the scarab beetle Anomala cuprea, each specific for one of the two pheromone component s (R)-buibuilactone and (R)-japonilure, respectively. No neurons were found that responded specifically to enantiomers of the pheromone compounds, i.e . (S)-buibuilactone and (S)-japonilure. Pheromone receptor neurons are pres ent in high numbers on both the male and the female antenna, with a lower s ensitivity in the females. As in bark beetles and moths, the pheromone rece ptor neurons in A. cuprea are very sensitive and selective. The difference in response thresholds between (R)- and (S)-enantiomers is almost three ord ers of magnitude. Pheromone receptor neurons are found in sensilla placodea located in a defined area on each lamella in the antennal club. (R)-buibui lactone and (R)-japonilure neurons are always found in different sensilla. Both types of sensilla contain two neurons, with the pheromone-sensitive ne uron displaying a high spike amplitude and the second neuron, not respondin g to any of the tested compounds, always with a lower spike amplitude.