Characterizing human odorant signals: insights from insect semiochemistry and in silico modelling

Interactions relating to human chemical signalling, although widely acknowledged, are relatively poorly characterized chemically, except for human axillary odour. However, the extensive chemical ecology of insects, involving countless pheromone and other semiochemical identifications, may offer insights into overcoming problems of characterizing human-derived semiochemicals more widely. Current techniques for acquiring insect semiochemicals are discussed, particularly in relation to the need for samples to relate, as closely as possible, to the ecological situation in which they are naturally deployed. Analysis is facilitated by chromatography coupled to electrophysiological preparations from the olfactory organs of insects in vivo . This is not feasible with human olfaction, but there are now potential approaches using molecular genetically reconstructed olfactory preparations already in use with insect systems. There are specific insights of value for characterizing human semiochemicals from advanced studies on semiochemicals of haematophagous insects, which include those involving human hosts, in addition to wider studies on farm and companion animals. The characterization of the precise molecular properties recognized in olfaction could lead to new advances in analogue design and a range of novel semiochemicals for human benefit. There are insights from successful synthetic biology studies on insect semiochemicals using novel biosynthetic precursors. Already, wider opportunities in olfaction emerging from in silico studies, involving a range of theoretical and computational approaches to molecular design and understanding olfactory systems at the molecular level, are showing promise for studying human semiochemistry. This article is part of the Theo Murphy meeting issue ‘ Olfactory communication in humans ’.

Influence of Adsorbent Nature on the Dynamic Headspace Study of Insect Semiochemicals

In chemical ecology studies (insect–insect, insect–plant relationships), it is important to choose the appropriate sampling methods and the correct optimization of sampling by using dynamic systems. In the present work, different adsorbents were evaluated in a dynamic system that presents a stream of purified air flowing through an aeration chamber containing a mixture of volatile organic compounds, mainly insect semiochemicals such as α-pinene, sulcatone, β-linalool, menthone, isomenthone, methyl salicylate, grandlure I, grandlure II, grandlure III, grandlure IV, eugenol, and α-ionone. Traditional adsorbents such as Tenax TA, Porapak Q, Hayesep Q, and activated charcoal were evaluated; further, alternatives such as Porapak Rxn RP, HLB, SCX, and silica gel, among others were proposed owing to their lower cost. The results demonstrated that Porapak Q and Porapak Rxn RP, despite their different chemical composition, were able to produce similar ratios of compounds to that of the reference solution and, moreover, with the highest recovery yields. However, it is important to emphasize the adsorption selectivity provided by SCX for eugenol and α-ionone. When Porapak Rxn RP was used in the analysis of Eucalyptus globulus volatiles, excellent results were obtained, and these agree with reported data from a hydrodistillation method.

Morphology and Release Profile of Microcapsules Encapsulated Alpha-Pinene by Complex Coacervation

The chitosan-gum arabic microcapsules prepared by complex coacervation were chosen as carrier for a model insect semiochemicals, α-pinene, owing non-toxicity of the polymers and mild conditions of the method. The coated colloids were characterized using scanning electron microscopy (SEM). The release of α-pinene from microspheres was studied in simulated conditions. The results showed that α-pinene-loaded microspheres which were obtained by association had a mean diameter of 5±0.5µm. The encapsulation efficiency and the encapsulation yield of the α-pinene-loaded microspheres were about 51.70±2.5% and 42.11±2.3%, respectively. The release experiments revealed that polyelectrolytes prolonged the release time of the encapsulated α-pinene. The release rate of α-pinene from the microspheres was proportional to the release time.