Molecules and macromolecules involved in chemical communication of scarab beetles
Chemical communication involves the production and release of specific chemicals (pheromones and other semiochemicals) by the emitter, and the detection and olfactory processing of these signals leading to appropriate behavioral responses in the receiver. In contrast to most of the scarab species investigated to date, the Japanese and Osaka beetles have the ability to detect the allospecific pheromone, which plays a pivotal role in the isolation mechanism between these two species. Each species produces a single enantiomer of japonilure [(Z)-5-(dec1-enyl)oxacyclopentan-2-one], but they have evolved the ability to detect both enantiomers, one as an attractant and the other as a behavioral antagonist (stop signal). There is growing evidence in the literature that the inordinate sensitivity and selectivity of the insect olfactory system is achieved by a combination of various olfactory-specific proteins, namely, odorant-binding proteins (OBPs), odorant receptors (ORs), and odorant-degrading enzymes. The relationship between the pheromone structures and the primary sequences of the proteins suggest that OBPs play a part in the selectivity of the olfactory system in scarab beetles by "filtering" chemical signals during the early olfactory processing (perireceptor events). Nevertheless, it is unlikely that pheromone-binding proteins are "chiral filters" as the Japanese and Osaka beetles each possess only one single binding protein. Upon interaction with negatively charged membranes, OBPs undergo conformational changes that may lead to the release of the ligands.