Male-Produced Sex Pheromone of the Carrion Beetles, Oxelytrum discicolle and its Attraction to Food Sources

Abstract

Carrion beetles are part of the great diversity of insects collected on cadavers. In Brazil, beetles of the genus Oxelytrum have great forensic importance in post mortem interval (PMI) estimation. We investigated the system of chemical communication in the attraction of these necrophagous beetles. Gas chromatographic analysis (GC) of female and male aeration extracts revealed the presence of two male-specific compounds, produced in a ratio of 94:6. Bioassays showed that the combination of male produced volatiles and the odor of a food source (carcass volatiles) were attractive to females. Mass and infrared spectral analyses of the male-specific compounds suggested that they were both unsaturated hydrocarbons. Several micro-derivatizations were carried out with the natural products, and the target structures were identified as (Z)-1,8-heptadecadiene (major) and 1-heptadecene (minor). The structure of the minor component was assigned by co-injection with a commercial standard. A seven-step synthesis was developed to synthesize (Z)-1,8-heptadiene, which co-eluted with the major natural product on three different GC stationary phases. Y-tube olfactometer assays showed that the mixture of synthetic standards in the naturally occurring proportion was slightly attractive to females. The results contribute both to the understanding of the chemical ecology of O. discicolle and to its potential to improve the accuracy of PMI estimation.

Diel Activity and Effect of Carcass Decomposition on the Attractiveness to the Forensically Important SpeciesOxelytrum Discicolle(Coleoptera: Silphidae)†

“…The slightly greater number of female specimens collected in the preference experiment indicates a selection for more decomposed bodies as substrates for food and egg‐laying. However, it is important to consider the biochemical cues involved, as males of O. discicolle tend to arrive early and release a pheromone to attract female partners for mating . This early pattern of arrival is not manifested in the overall abundance throughout the decomposition which suggests that the proportion of females shows a tendency to increase with time.…”

“…The use of carrion as food and as a site for mating or oviposition by beetles does not occur randomly; on the contrary, behavioral and physiological processes determine the selection of the appropriate resource, mediated by visual and, particularly, olfactory cues . Beetles locate and colonize carcasses if the physical and chemical properties of the substrate indicate suitable conditions for the survival and development of their offspring . In that context, beetles will respond differently to carcasses and cadavers at different stages of decomposition.…”

Identification and synthesis of the male produced volatiles of the carrion beetle, Oxelytrum erythrurum (Coleoptera: Silphidae)

“…In O. discicolle, females are not attracted to the male pheromone alone, but only in the presence of a carcass, apparently revealing an association of reproduction and oviposition site. 8 So, we expect that the two compounds herein identified are the male produced sex pheromone of O. erytrhurum. Thus, studying the chemical ecology of necrophagous species creates an important chemotaxonomic identification tool, which could be easier than comparing the external morphology of closely related species, such as O. discicolle and O. erythrurum.…”

“…3 Despite a few existing papers addressing their occurrence 5,6 and feeding habits, 7 only recently has the chemical ecology of O. discicolle been studied, revealing the existence of a male produced sex pheromone composed by a major and a minor component, (Z)-1,8-heptadecadiene and 1-heptadecene, respectively. 8 Because of the taxonomic proximity and the similarities concerning the feeding habits and the habitat of O. discicolle and O. erythrurum, the objective of this study was to identify and synthetize the chemical compounds produced by O. erythrurum using the same methodology applied by Fockink et al 8 for O. discicolle.…”

“…2-(9-bromononyloxy)-tetraydro-2H-pyran (5) was prepared from 1,9-nonanediol (3), which suffered a monobromination 20 and was subsequently protected with DHP. 21 The ether (5) was alkylated with the anion generated with n-BuLi from 1-decyne (6), providing the intermediate 7, 22 which was de-protected to yield the alcohol (8). 23 The stereoselective reduction of the alcohol (8) with H 2 over Pd/CaCO 3 (Lindlar's reagent) resulted in the alcohol (9).…”