Molecules and macromolecules involved in chemical communication of scarab beetles

Abstract

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. PHEROMONE CHEMISTRYRecent 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 compounds [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 isolation [5,6]. Species that have the same pheromone system are isolated either temporarily or geographically. 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. japonica 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 enantiomeric pheromones have evolved as part of the isolation mechanism...

Revisiting trends in morphology of antennal sensilla in scarabaeoid beetles

“…Also, among other Pleurosticts (i.e., the paraphyletic "Melolonthinae", Cetoniinae, and Rutelinae), there are some quite speciespoor lineages and slowly diverging lineages with "modern" sensilla (Table 1). Hence, we see the here presented hypotheses and results as a starting point to refine our phylogenetical understanding of the Scarabaeoidea but most of all to open up for a molecular characterization of antennal sensilla functionality, regarding pheromones and odor binding proteins of sensilla (e.g., Leal 2001;Nikonov et al 2002;González-González et al 2019) to improve our understanding of their chemical communication, ecology and evolution.…”

Insect host location: a volatile situation

“…31 Por lo general, en insectos, la percepción del olfato se realiza a través de sensilias especializadas con receptores olfatorios (ORs) en las antenas. 187 En la ecología química existen distintos tipos de bioensayos que favorecen la identificación como semioquímicos de compuestos orgánicos volátiles identificados en los sistemas de estudio. Entre estos se encuentran aproximaciones electrofisiológicas tales como las técnicas de electroantenografía (EAG) que pueden ser independientes o acopladas como detectores a técnicas de separación por cromatografía de gases (GC-EAD).…”

NMR structure reveals intramolecular regulation mechanism for pheromone binding and release

“…This and the observation that a number of OBPs, including BmPBP, do not bind ligands below pH 5.0 (8,9) suggests that pH variation of the folded conformation might play a physiological role in olfaction (10,11). In this context, it is intriguing that near-UV circular dichroism measurements revealed that BmPBP undergoes a conformational transition when mixed with model membranes (12).…”