Enantiomeric Anosmia in Scarab Beetles

Abstract

The sex pheromone for Anomala octiescostata has been previously identified as a 4:1 mixture of (R)-buibuilactone and (R)-japonilure. Field experiments showed that although not active per se, the secondary component increased the activity of major component, buibuilactone. The enantiomers of these semiochemicals, i.e., (S)-buibuilactone and (S)-japonilure are neither attractants nor behavioral antagonists to the pheromone system of A. octiescostata. Chiral GC-EAD experiments demonstrated that, in marked contrast to the Japanese beetle and Osaka beetle, which can detect a stereoisomer not produced by their conspecific females, the male antennae of A. octiescostata lack olfactory receptor neurons (ORNs) tuned to (S)-buibuilactone. The same enantiomeric anosmia (inability to smell a compound) was also observed in Anomala cuprea male antennae. Both in a Y-olfactometer and field experiments, it was clarified that (S)-buibuilactone was not a behavioral antagonist for A. cuprea. Contrary to male antennae of both A. octiescostata and A. cuprea, which lack ORNs tuned to the nonnatural (S)-buibuilactone, fragrance evaluation by skilled perfumers revealed that the human nose can discriminate (both in intensity and quality) enantiomerically pure samples of (R)- and (S)-buibuilactone and japonilure.