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

Abstract

Chemical communication in scarab beetles involves female-released long-distance sex pheromones. Electrophysiological recordings using tungsten microelectrodes demonstrated two types of olfactory receptor neurons in the scarab beetle Anomala cuprea, each specific for one of the two pheromone components (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 present in high numbers on both the male and the female antenna, with a lower sensitivity in the females. As in bark beetles and moths, the pheromone receptor neurons in A. cuprea are very sensitive and selective. The difference in response thresholds between (R)- and (S)-enantiomers is almost three orders of magnitude. Pheromone receptor neurons are found in sensilla placodea located in a defined area on each lamella in the antennal club. (R)-buibuilactone and (R)-japonilure neurons are always found in different sensilla. Both types of sensilla contain two neurons, with the pheromone-sensitive neuron displaying a high spike amplitude and the second neuron, not responding to any of the tested compounds, always with a lower spike amplitude.