Pure Appl. Chem., Vol. 73, No. 3, pp. 613–616, 2001. © 2001 IUPAC 613 Molecules and macromolecules involved in chemical communication of scarab beetles* Walter Soares Leal Department of Entomology, University of California, Davis, CA 95616 USA Abstract: Chemical communication involves the production and release of specific chemicals (pheromones and other semiochemicals) by the emitter, and the detection and olfactory pro- cessing of these signals leading to appropriate behavioral responses in the receiver. In con- trast 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 japonil- ure [(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, name- ly, 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. PHEROMONE CHEMISTRY Recent studies have led to the identification of the sex pheromones of various species in the subfamily Rutelinae and Melolonthinae [1]. In general, the pheromones of the former are fatty acid-derived com- pounds [2], whereas the latter utilizes phenolic, terpenoid, and amino acid-derived compounds. Two interesting exceptions to this general rule are the pheromones of Heptophylla picea and Phyllopertha diversa. Although belonging to the Melolonthinae, H. picea utilizes (R,Z)-7,15-hexadecadien-4-olide [3], most likely biosynthesized from stearic acid. On the other hand, P. diversa (Rutelinae) produces an intriguing alkaloid pheromone, which also has medicinal properties [4]. Utilizing pheromone blends that consist of just a few semiochemicals or even a single constituent, closely related species have attained isolated chemical communication channels and reproductive iso- lation [5,6]. Species that have the same pheromone system are isolated either temporarily or geograph- ically. Interestingly, Anomala osakana and Popillia japonica utilize enantiomers of a chiral pheromone (japonilure), with one stereoisomer being an attractant and the other a behavioral antagonist. P. japon- ica and A. osakana produce (R)- and (S)-japonilure, respectively [7,8]. The pheromone of one species is a behavioral antagonist for the other. It seems that this agonist–anatagonist activities of the enan- tiomeric pheromones have evolved as part of the isolation mechanism between these two species that *Lecture presented at the 22 nd IUPAC International Symposium on the Chemistry of Natural Products, São Carlos, Brazil, 3–8 September 2000. Other presentations are published in this issue, pp. 549–626.