Manuel Zarzo

The sense of smell: molecular basis of odorant recognition

Most animal species rely on odorant compounds to locate food, predators, or toxins. The sense of smell is also involved in animal communication, and revealing the underlying mechanisms will therefore facilitate a deeper understanding of animal behaviour. Since the 1940s different theories have speculated on the fundamental basis of olfaction. It was assumed that odorant molecules were recognized by selective protein receptors in the nose, triggering a nervous signal processed by the brain. The discovery of these receptors in the early 1990s allowed great progress in understanding the physiological and biochemical principles of olfaction. An overview of the different mechanisms involved in the coding of odour character as well as odour intensity is presented here, focusing on the biochemical basis of odorant recognition. Despite the enormous progress achieved in recent years, details of odorant‐receptor interaction at the molecular level and the mechanisms of olfactory receptor activation are poorly understood. The likely role of metal ions in odorant recognition is discussed, and also the perireceptor events involved in odorant transport and biotransformation, with a view to providing a comprehensive overview of mammalian olfaction to guide future computational structural models and the design of functional experiments. Recent studies have analysed the olfactory genome of several species, providing information about the evolution of olfaction. The role of the olfactory system in animal communication is also described.

Understanding the underlying dimensions in perfumers’ odor perception space as a basis for developing meaningful odor maps

Various low-dimensional perceptual maps of fragrances have been proposed in the literature, as well as sensory maps for the odor descriptors most frequently applied in perfumery. To reach a consensus, however, seems difficult, if at all possible. In the present study, we applied principal components analysis to two databases. The first contains numeric odor profiles of 309 compounds based on 30 descriptors. The loading plot corresponding to the relevant components was strikingly similar to the odor effects diagram proposed by P. Jellinek (1951), primarily on the basis of his long experience as a perfumer. We obtained similar results in our analysis of the second database, which comprises 66 descriptors and contains the semantic descriptions of 119 perfume materials. On the basis of the results of both analyses, a commercial map of fragrances is discussed. Our findings suggest that it is possible to develop standard sensory maps of perfumery odor descriptors, if a consensus is first reached regarding which odorants best represent particular odor qualities.

Hedonic Judgments of Chemical Compounds Are Correlated with Molecular Size

Different psychophysical works have reported that, when a wide range of odors is assessed, the hedonic dimension is the most salient. Hence, pleasantness is the most basic attribute of odor perception. Recent studies suggest that the molecular size of a given odorant is positively correlated with its hedonic character. This correlation was confirmed in the present study, but further basic molecular features affecting pleasantness were identified by means of multiple linear regression for the compounds contained in five chemical sets. For three of them, hedonic judgments are available in the literature. For a further two chemical sets, hedonic scores were estimated from odor character descriptions based on numerical profiles. Generally speaking, fairly similar equations were obtained for the prediction of hedonic judgments in the five chemical sets, with R2 values ranging from 0.46 to 0.71. The results suggest that larger molecules containing oxygen are more likely to be perceived as pleasant, while the opposite applies to carboxylic acids and sulfur compounds.

Long-Term Monitoring of Fresco Paintings in the Cathedral of Valencia (Spain) Through Humidity and Temperature Sensors in Various Locations for Preventive Conservation

We describe the performance of a microclimate monitoring system that was implemented for the preventive conservation of the Renaissance frescoes in the apse vault of the Cathedral of Valencia, that were restored in 2006. This system comprises 29 relative humidity (RH) and temperature sensors: 10 of them inserted into the plaster layer supporting the fresco paintings, 10 sensors in the walls close to the frescoes and nine sensors measuring the indoor microclimate at different points of the vault. Principal component analysis was applied to RH data recorded in 2007. The analysis was repeated with data collected in 2008 and 2010. The resulting loading plots revealed that the similarities and dissimilarities among sensors were approximately maintained along the three years. A physical interpretation was provided for the first and second principal components. Interestingly, sensors recording the highest RH values correspond to zones where humidity problems are causing formation of efflorescence. Recorded data of RH and temperature are discussed according to Italian Standard UNI 10829 (1999).

Mediterranean fruit fly suppression using chemosterilants for area-wide integrated pest management.

BACKGROUND The chemosterilisation technique has been demonstrated to reduce the population and fruit damage of the Mediterranean fruit fly, Ceratitis capitata (Wiedemann), in citrus orchards. Field trials showed efficacy by reducing the fruit fly population, which was progressively achieved by continuous application of lufenuron to several generations. Different authors have suggested that field trials should be carried out in isolated or wide areas in order to reduce fruit fly intrusion and obtain best results. To this end, a wide-area trial over 3600 hectares has been under investigation in Valencia (Spain) since 2002 to validate the chemosterilisation technique against the fruit fly. The whole area was treated with 24 traps ha(-1), using more than 86,000 traps in the field trial. RESULTS A continuous decrease in fruit fly population was observed over the 4 years under trial. Moreover, results showed a significant reduction in persimmon damage in the chemosterilant treatment area compared with a malathion aerial treatment area. In the case of citrus damage, no significant differences were obtained between malathion and chemosterilant treatments. CONCLUSION The chemosterilant method reduces Mediterranean fruit fly populations, and therefore it is a candidate treatment to replace aerial treatments with insecticides in order to suppress this pest. In addition, the efficacy of chemosterilant treatment is increasing year after year. The possibility of using this technique combined with other control methods is discussed.

Microclimate monitoring of Ariadne’s house (Pompeii, Italy) for preventive conservation of fresco paintings

BackgroundAriadne’s house, located at the city center of ancient Pompeii, is of great archaeological value due to the fresco paintings decorating several rooms. In order to assess the risks for long-term conservation affecting the valuable mural paintings, 26 temperature data-loggers and 26 relative humidity data-loggers were located in four rooms of the house for the monitoring of ambient conditions.ResultsData recorded during 372 days were analyzed by means of graphical descriptive methods and analysis of variance (ANOVA). Results revealed an effect of the roof type and number of walls of the room. Excessive temperatures were observed during the summer in rooms covered with transparent roofs, and corrective actions were taken. Moreover, higher humidity values were recorded by sensors on the floor level.ConclusionsThe present work provides guidelines about the type, number, calibration and position of thermohygrometric sensors recommended for the microclimate monitoring of mural paintings in outdoor or semi-confined environments.

Study on the optimum pheromone release rate for attraction of Chilo suppressalis (Lepidoptera: Pyralidae).

ABSTRACT Traditional chemical control against Chilo suppressalis Walker is currently being replaced in Spain by new methods based on pheromones. A key step to improve the efficacy of these methods is the determination of the optimum pheromone release rate, which is still uncertain for this pest. In this work, the pheromone release profile and the field performance of a new mesoporous dispenser was compared with a standard commercial dispenser. For this purpose, pheromone loads were extracted from field-aged dispensers and quantified by gas chromatography with flame ionization detector. In addition, a field trial was carried out with traps baited with one, two, or three mesoporous dispensers per trap, as well as with traps containing one standard dispenser. We found that the highest number of field catches did not correspond to the highest pheromone emission rate, which suggests a repellent effect of the insect if the emission is excessive. The results suggest that the attractant activity was maximized by emitting ∼34 µg/d. The efficacy of the mesoporous dispenser and its possible improvements are discussed.

Solid phase microextraction of volatile emissions of Ceratitis capitata (Wiedemann) (Diptera: Tephritidae): influence of fly sex, age, and mating status.

Considerable efforts have been devoted to understanding the courtship behavior and pheromone communication of medflies; however, the sex pheromone composition is still a controversial subject. The discovery of new components affecting medfly behavior would be of interest for medfly control methods based on semiochemicals. This work describes volatile compounds emitted by Ceratitis capitata collected using solid phase microextraction. The volatile study was conducted according to an experimental design with three factors (sex, age, and mating status) assumed to be relevant for better understanding the chemical communication. Emission data were treated by means of principal component analysis, a statistical methodology not previously applied to the study of volatiles emitted by fruit flies. The characterization of emission patterns could be useful for the selection of compounds to be further investigated in biological assays to improve knowledge of the key semiochemicals involved in medfly behavior.

Dispersal ability of Ceratitis capitata (Diptera: Tephritidae): edge effect in area-wide treatments

Bait stations are widely used to control Ceratitis capitata, even though the effect of intrusion from untreated areas decreases the efficacy of the technique. In this work, the edge effect of outer fruit fly populations from untreated areas and backyard orchards has been studied. For this purpose, a field trial was carried out during four years in a wide area of 10 000 ha located in Valencia (Spain). The main growing species were Prunus persica, Prunus domestica, Citrus sinensis, Citrus reticulata and Diospyros kaki. An area of 3,600 ha was treated with chemosterilant bait stations. Fruit fly populations were monitored during the 4 years of study inside and outside the treated area using Tephri‐traps baited with trimedlure. A grid of 180 traps was placed in the field with an intertrap distance of 450 m. Multiple linear regression was applied to model population levels as a function of distance to untreated areas and backyards. The distance at which outer medfly populations influenced the treated wide‐area population was about 1.3 km. This value reflects the distance at which a given fruit fly population is influenced by outer populations and suggests that C. capitata is able to move more than 1 km seeking for hosts. Thus, buffer areas in area‐wide integrated pest management of Mediterranean fruit fly should be at least 1.3 km wide.

Effect of Functional Group and Carbon Chain Length on the Odor Detection Threshold of Aliphatic Compounds

Odor detection thresholds (ODTs) are used for assessing outdoor and indoor air quality. They are obtained experimentally by olfactometry and psychophysical methods, and large compilations are available in the literature. A non-linear regression equation was fitted to describe the ODT variability of 114 aliphatic compounds based on the alkyl chain length for different homologous series (carboxylic acids, aldehydes, 2-ketones, esters, 1-alcohols, amines, thiols, thioethers and hydrocarbons). The resulting equation reveals an effect of the functional group, molecular size and also an interaction between both factors. Although the mechanistic interpretation of results is uncertain, the relatively high goodness-of-fit (R2 = 0.90) suggests that ODT values of aliphatic compounds can be predicted rather accurately, which is not the case for rigid molecules. This equation may serve as a basis for the development of more complex ODT models taking into account diverse structural features of odorants. The variability of power-law exponents was also investigated for the homologous series.