Molecular Basis of Pheromone Reception and Signal Inactivation in Moths and Beetles

Abstract

Insects perceive semiochemicals with remarkable selectivity and sensitivity. The process starts with detection of odorants by specialized sensilla such as sensilla trichodea in moths and sensilla placodea in scarab beetles. These sensilla house odorant receptor neurons (ORNs) whose odorant receptors (ORs) are compartmentalized by an aqueous solution (sensillar lymph). Odorant- and pheromone-binding proteins (OBPs and PBPs) serve as liaison between the external environment and the ORs. Recent studies are unveiling the functions of PBPs, their structural features, in particular, binding specificity determinants, and details of the protection and release of pheromones. By contrast, the basis of pheromone signal inactivation is terra incognita; two hypotheses are yet to be tested: enzymatic degradation and molecular trapping. Esterases and other insect antennae-specific pheromone-degrading enzymes have been reported, but to date they have never been fully characterized. Antennae-specific esterase(s) from the Japanese beetle have a significant preference for the pheromone, (R)-japonilure, with slower degradation of the behavioral antagonist, (S)-japonilure. These findings led to the hypothesis that kinetics of pheromone inactivation plays a significant part in the chiral discrimination by the Japanese beetle.