In recent years, there has been a great deal of research on olfaction in organisms at the molecular level, and a database of responses to various odorants has been compiled. Insects, in particular, have an excellent ability to detect odorants, and their olfactory mechanisms have been remarkably elucidated based on genetic engineering methods. Therefore, we are focusing on the olfactory system of insects and investigating the use of insect olfactory receptors and organisms for the application of odorant sensors. In this article, we describe the use of the insect olfactory receptor expression system in heterologous cells and the production of transgenic silkmoths for development of odorant biosensors.

Insect olfactory receptors have both excellent sensitivity and selectivity. Such an olfactory receptor is expected to be utilized as an odorant sensor by incorporating it into electronic devices. We have developed a biohybrid odor sensor that consists of a mosquito olfactory receptor reconstituted in a lipid bilayer membrane formed by the droplet contact method. When using the olfactory receptors as a sensor, the poor solubility of odorants in water becomes a serious problem. In this paper, we describe the device that effectively introduce odorants into aqueous droplets, and present an odorant sensing robot and a breath diagnosis system.

Studies on the sex pheromones of insects have been motivated by the expectation of possible application in pest management. At the first stage of the study, sex pheromones of moth species were explored extensively partly because many important crop pests belong to lepidoptera. In this article, mechanisms that underlie the production of species-specific sex pheromones in moths are explained in detail with reference to their biosynthetic routes and enzymes involved therein. I then refer to the recent attempts to produce insect sex pheromones in plants and yeasts. Lastly, recent progress in studies on sex pheromones of some non-lepidopterous insects, mealybugs, aphids, and longhorn beetles, will also be briefly reviewed.

Ants, which are eusocial insects, exhibit disciplined behavior based on a nest (colony) consisting of a small number of reproductive and a large number of worker ants in a common body odor. In particular, one of the most important rules for the behavior of elder workers having foraging task out of the nest is the identification rule for recognizing the nest mates as “friends” and the non-nestmate as “enemies”. Focusing on the hydrocarbon sensillum having a novel micro-network among receptor neurons responsible for a robust friend and enemy discrimination, we explain the mechanism to establish this rule through the molecule(s), cell(s), and individual(s) levels. We also introduce the possibility of using the code of conduct for identifying enemies to prevent the invasion and expansion of alien ant species that threaten the biodiversity of native ecosystems.

Fruit fly species in the family Tephritidae include many serious pests. Their life cycle is affected by various semiochemicals. Among them, plant volatiles have remarkable effects on their reproductive and host-finding behaviors. Therefore, the characterization of olfactory receptors that respond to plant volatiles is important to gain insights into the chemosensory mechanisms underlying the adaptation to surrounding environments via chemoreception at the molecular level. Since next-generation sequencers are available, a large number of chemosensory-related genes have been identified in tephritid fruit flies. Characterization of orphan chemosensory receptors is the first step in the elucidation of chemosensory mechanisms. Here, I review the recent progression of functional analyses of olfactory receptors identified from tephritid fruit flies, focusing on our studies on olfactory receptors that respond to plant volatiles.

Inhalation of the aroma of second flush Darjeeling tea elevated peripheral skin temperature and miosis rate more significantly compared to inhalation of Assam tea and Uva tea aromas, suggesting that Darjeeling tea has a strong sedative effect due to inhibition of sympathetic nerve activity correspondingly making parasympathetic nerve activity dominant. On the supposition that aroma components specific to Darjeeling tea were contributing to the overall sedative effect, analysis of the aroma components was performed and the characteristic aroma compounds, Geraniol, Hotrienol, 2,5-Dimethyl-4-hydroxy-3(2H)-furanone, 2-Phenylethyl alcohol were identified and selected. When each of these four aroma compounds was inhaled at equivalent concentrations while drinking tea, only Hotrienol showed a significant increase in miosis rate. Further, we studied the dose-dependency and found there was a significant increase in miosis rate with a low Hotrienol concentration of not more than 5ppm. Peripheral skin temperature also increased after inhalation of Hotrienol. Collectively, these findings indicate that Hotrienol is the most important compound contributing to the sedative effect of second flush Darjeeling tea aroma.

Recognition-basis odor concentration measurement method (RO cm method), which is superior to odor intensity reduction measurement method (OIRM method) in objectivity, was proposed to measure sensory deodorizing effect. This study, in order to evaluate the usefulness of the RO cm method, the comparison of deodorization effect of several deodorants was confirmed, and the usefulness as an evaluation method of the deodorization effect was evaluated in comparison with the OIRM method. As the result, the RO cm method allowed the identification of odor index difference of half of odor index even in the presence of fragrance, which is equivalent to the odor intensity difference of 1.

In the RO cm method, the significant difference was shown on the difference between 2 fragrances in which the OIRM method could not show the difference of the sensory deodorizing effect. This result agrees with the evaluation result got from the general consumer answer.