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Natural odor ligands for olfactory receptor neurons of the female mosquito Aedes aegypti: Use of gas chromatography-linked single sensillum recordings
Abstract
Female Aedes aegypti are vectors of dengue and yellow fever. Odor volatiles are the predominant cues that drive the host-seeking behavior of Ae. aegypti. Odorant molecules are detected and discriminated by olfactory receptor neurons (ORNs) housed in sensory hairs, sensilla, located on the antennae and maxillary palps. In a previous study, we used odor volatiles that are behaviorally and/or electrophysiologically active for Ae. aegypti and other mosquito species to show that antennal ORNs of female Ae. aegypti are divided into functionally different classes. In the present study, we have, for the first time, conducted gas chromatography-coupled single sensillum recordings (GC-SSR) from antennal trichoid and intermediate sensilla of female Ae. aegypti in order to screen for additional putative host attractants and repellents. We used headspace collections from biologically relevant sources, such as different human body parts (including feet, trunk regions and armpit), as well as a plant species used as a mosquito repellent, Nepeta faassenii. We found that a number of ORN types strongly responded to one or more of the biological extracts. GC-SSR recordings revealed several active components, which were subsequently identified through GC-linked mass spectrometry (GC-MS). Electrophysiologically active volatiles from human skin included heptanal, octanal, nonanal and decanal.
... The EAD method has achieved considerable success, including the detection of responses to (a) heptanal, octanal, nonanal and isobutyric acid in the sucking bug, Triatoma infestans (Guerenstein and Guerin 2001), (b) several compounds, particularly the 2-ketones and lactone in tsetse flies (Gikonyo et al. 2002), (c) heptanal, octanal, nonanal and decanal in mosquitoes (Ghaninia et al. 2008), (d) C7-C10 aldehydes and sulcatone in bed bugs (Harraca et al. 2012), advanced decay of rats in the fringed larder beetle, Dermestes frischii (Martin et al. 2020), and (e) 1-octen-3-ol, dimethyldisulfide (DMDS), 2-phenylethanol, dimethyl trisulfide (DMTS), butyric acid, and indole in L. cuprina (Park and Cork 1999;Yan et al. 2018). ...
... Finally, it is important to recognise that laboratory behavioural assays need to be supported by field testing to ensure that hypotheses developed with laboratory-reared insects in a controlled environment translate to the real world. It is well documented that semio-chemicals from livestock pelage can evoke antennal responses in a variety of insect pests (Guerenstein and Guerin 2001;Gikonyo et al. 2002;Ghaninia et al. 2008;Syed and Leal 2009;Harraca et al. 2012), yet, rarely seem to illicit positive behavioural responses in the field. Thus, in wild L. cuprina under field conditions, the antenna and behavioural responses could differ among individual semio-chemicals, or mixes of semio-chemicals. ...
... Moreover, as mentioned above, we need to remember that semio-chemicals that come strongly to the fore under laboratory testing might not be important under field conditions. For example, octanal and nonanal, both of which have been identified previously in extracts of livestock pelage and are known to evoke antennal responses in a variety of insect pests (Guerenstein and Guerin 2001;Gikonyo et al. 2002;Ghaninia et al. 2008;Syed and Leal 2009;Harraca et al. 2012), rarely seem to illicit positive behavioural responses in the field. ...
Breech flystrike is a painful, debilitating and potentially lethal disease caused by the larvae of the blowfly, Lucilia cuprina, and, despite many years of research, it remains a serious financial and animal-welfare issue for the Merino sheep industry in Australia. The common methods of prevention, namely insecticides, crutching and 'mulesing', are problematical, so alternative approaches are needed. Breeding for resistance to breech strike is a fundamentally attractive proposition, but the trait itself is difficult and expensive to quantify in large numbers of sheep in extensive production systems. Several indirect traits are correlated with susceptibility to flystrike, but a large proportion of the variation in susceptibility remains unexplained. The common thread through those indirect traits is odour, so we turned to the biology of insect olfaction and its role in fly-sheep interactions. L. cuprina uses odours to detect and locate potential hosts over long distances, to guide orientation and landing behaviour, and to select egg-laying sites. Preliminary studies demonstrated the importance of confining our work to gravid female L. cuprina, and also validated the use of flies reared in the laboratory for experimentation. Using laboratory-reared flies and a combination of gas chromatography-mass spectrometry with electroantennographic detection, we identified odouriferous compounds from sheep that the antenna of L. cuprina can detect. To determine whether the identified compounds were attractive or repulsive, we needed to use a behaviour test. In preliminary studies, we compared four behaviour bioassays (Y-tube, landing time, visiting frequency, and trap) and found the trap to be the most effective. We observed that L. cuprina was attracted by several compounds in Merino wool, including octanal, nonanal and dimethyl trisulfide. We also found that the wool levels of octanal and nonanal are heritable in Merino sheep, suggesting that these compounds might be useful as traits in selection for flystrike resistance. Another possibility is that these olfactory-active compounds might guide efforts to modify the genome of sheep, or perhaps even L. cuprina. Success in these endeavours could save as much as A$200 m per year for the Australian Merino-based industries, while also improving the image of wool in world markets.
... However, the entomological surveillance phase is the most complex in the process of control of the transmission of Trypanosoma cruzi, the causal agent of Chagas disease, and therefore more powerful tools for early detection of the presence of triatomines in dwellings are required to achieve effective control 5,25 because it is practically impossible to interrupt the transmission of T. cruzi due to the variety of existing zoonotic cycles and the large number of vectors that transmit this parasite. 26 The importance of aldehydes in the sensory ecology of hematophagous arthropods, such as ticks, 27 triatomines, 1 mosquitoes, 28,29 and flies, 30 has been widely described. Our research group previously conducted field studies on the effectiveness of long-chain aldehydes as attractants for T. infestans. ...
To assess the attracting capacity of aliphatic and aromatic aldehydes to Triatoma infestans , the Chagas disease vector, laboratory tests were conducted using individual compounds and mixtures to evaluate their potential use in baited traps for intradomicile population dynamics analysis. Commercial samples of hexanal, nonanal, and benzaldehyde were used at 95% purity. The experiments were performed at 25°C and 65% relative humidity using two procedures: a glass arena with filter papers impregnated with 1, 5, and 10 μL of the tested compounds and a double-choice olfactometer. Attraction was scored positively if the insect remained more than 30 seconds on one of the surfaces. The results of the study showed that hexanal was attractive to females at higher concentrations (5–10 μL; P < 0.0001), and IV instar nymphs were only attracted at the highest concentration (10 μL; P < 0.01). Nonanal was attractive to IV instar nymphs at 1 and 5 μL ( P < 0.0001), whereas males and females were more attracted at 1 μL ( P < 0.01 and P < 0.05, respectively). Benzaldehyde showed significant differences with respect to controls, attracting females at low concentrations (1 μL; P < 0.0001) and IV instar nymphs at 5 and 10 μL ( P < 0.0001 and P < 0.001, respectively). In the olfactometer, the 60:40 hexanal/nonanal mixture was the most effective. In conclusion, this study demonstrated that the aliphatic and aromatic aldehydes studied here, both individually and in mixtures, could be used as effective attractants for T. infestans in intradomicile-baited traps. These results suggest that mixtures of these compounds could be implemented in field trials for Chagas disease surveillance.
... It has been reported that volatile organic compounds (VOCs) measured in skin gas, as well as in exhaled breath, may be markers of liver disease [14] and diabetes [15]. In addition, the content of skin gas may be related to biological phenotypes that cannot been detected using the exhaled breath, such as age [16], severe burn status [17], and attractiveness to mosquitoes [18]. This is because the composition of skin gas differs from that of exhaled breath [19]. ...
Background and aim
Numerous women of reproductive age experience physical or mental discomfort during their natural menstrual cycle due to paramenstrual symptoms, such as premenstrual syndrome (PMS). To date, there is no established biomarker for the diagnosis of PMS. This study investigated the relationship between skin gas composition and menstruation cycles, and evaluated the possibility of skin gas composition as a biomarker of paramenstrual symptoms.
Methods
We conducted an exploratory pilot study. Healthy Japanese women (aged 20–29 years) underwent blood and skin gas analyses on 1 day corresponding to menstruation, preovulatory, middle luteal, and late luteal phases. Skin gas was collected from the cubital fossa and armpit using a Passive Flux Sampler; samples were analyzed for 65 volatile organic compounds (VOCs) by gas chromatography-mass spectrometry (GC-MS). Non-parametric statistical analysis was performed to identify VOCs related to the menstrual cycle, levels of female hormones, and severity of PMS.
Results
Fourteen women participated; of those, 12 completed the study. Regarding the relationship with the menstrual cycles, seven and four VOCs were significantly and marginally changed, respectively, at the cubital fossa during menstruation. Of those 11 compounds, 10 were also correlated with the levels of serum female hormones. At the armpit, five and three compounds were significantly and marginally changed, respectively, during menstruation. Of those eight compounds, five were also correlated with the levels of serum female hormones. In the study of PMS severity, analysis of the changes in VOCs suggested that ketones and fatty acids are increased during menstruation in the severe PMS group versus the mild PMS group.
Conclusions
The results of this study suggest that certain VOCs emitted in skin gas related to the menstrual cycle, levels of female hormones, and severity of PMS. These findings may advance the metabolic understanding and development of diagnostic biomarkers for menstruation-related symptoms.
... Moreover, the types and the proportions of components vary considerably between different host species 8,58 and among different members of the same host species 59,60 . These components, even individually, can be detected by the mosquito olfactory system, as confirmed by the measurements of receptor responses 9,10,59,[61][62][63][64][65][66][67] . The individual components can also generate specific behavioral preferences in mosquitoes [68][69][70][71][72] . ...
Among the cues that a mosquito uses to find a host for blood-feeding, the smell of the host plays an important role. Previous studies have shown that host odors contain hundreds of chemical odorants, which are detected by different receptors on the peripheral sensory organs of mosquitoes. But how individual odorants are encoded by downstream neurons in the mosquito brain is not known. We developed an in vivo preparation for patch-clamp electrophysiology to record from projection neurons and local neurons in the antennal lobe of Aedes aegypti . Combining intracellular recordings with dye-fills, morphological reconstructions, and immunohistochemistry, we identify different sub-classes of antennal lobe neurons and their putative interactions. Our recordings show that an odorant can activate multiple neurons innervating different glomeruli, and that the stimulus identity and its behavioral preference are represented in the population activity of the projection neurons. Our results provide a detailed description of the second-order olfactory neurons in the central nervous system of mosquitoes and lay a foundation for understanding the neural basis of their olfactory behaviors.
... . Female mosquitoes spread the disease- 18 causing pathogens while feeding on human blood, which they require to complete their 19 reproductive cycle (Ariani et al., 2015;Dimond et al., 1955;Kogan, 1990). Mosquitoes 20 rely on various sensory stimuli, including visual, thermal, and olfactory cues, and 21 humidity, to find a suitable host for blood-feeding (Cardé, Odors are detected by olfactory receptor neurons (ORNs) housed in hair-like structures 30 called sensilla (Davis & Sokolove, 1976; Ghaninia et al., 2007Ghaninia et al., , 2008; Kellogg, 1970). Three 31 gustatory receptors -Gr1, Gr2, and Gr3 -are the sole detectors of CO2 in Aedes aegypti 32 (Jones et al., 2007;McMeniman et al., 2014). ...
Carbon dioxide (CO2) is one of the prominent sensory cues used by mosquitoes to find hosts for blood-feeding. CO2 is detected on the maxillary palps by capitate peg sensory neurons, whose axons project to the antennal lobe in the brain. Behavioral studies have shown that mosquitoes prefer non-homogenous plumes of CO2 over homogenous plumes and CO2 greatly enhances the attractiveness of lactic acid, a skin volatile. However, the neural mechanisms underlying these behavioral preferences are not known. Using in vivo intracellular recordings from projection neurons and local neurons in the antennal lobe, along with single sensillum recordings from the maxillary palps, we checked the representations of CO2 in the first two layers of the Aedes aegypti olfactory system. We found that the preference to non-homogeneous plumes of CO2 and its synergistic attraction with lactic acid are encoded in the PN population responses. Our results provide a foundation for understanding CO2-mediated host-attraction in mosquitoes.
... However, the distribution of this sensillum type on the antenna varies greatly across insect families. Most of the work on the GP has been done in D. melanogaster showing that it is tuned to carboxylic acids and amines, expresses olfactory receptors of the ionotropic receptor family but also plays a role in other sensory modalities (Meijerink et al., 2001;Yao et al., 2005;Ghaninia et al., 2008). ...
Many long-legged Medetera flies are natural enemies of bark beetle pests, which they detect using olfactory cues, likely through olfactory sensilla on the antennae and maxillary palps. Morphological characterisation of olfactory sensilla among insects can provide a basis for future taxonomic, phylogenetic or electrophysiological studies. Scanning electron microscopy was used to describe the morphology of olfactory organs and sensillar equipment of Medetera signaticornis and M. infumata. Three different olfactory sensillum types were found in both fly species, sensilla trichodea, s. basiconica and grooved pegs. Based on size and wall structure, s. trichodea and s. basiconica were categorised into different subtypes. Sharp-tipped curved s. trichodea, and small, large and thin s. basiconica were found on the antennal postpedicel of M. signaticornis adults, while grooved s. basiconica were found in M. infumata. The density of sharp-tipped long s. trichodea was significantly higher in males compared to females, and in M. signaticornis compared to M. infumata. Long-grooved s. basiconica were found grouped in a small pit on the maxillary palps of both species. Comparison of our results with the limited available ecological data suggests that differences in numbers of specific sensillum types may reflect adaptations related to olfactory-driven behaviours such as host seeking.
Aromatherapy is a medical practice that uses aromatic compounds or essential oils to influence mood and health. Essential oils used in aromatherapy are created from a wide variety of medicinal plants, flowers, herbs, roots, and trees that are found all over the world and have significant, well-documented benefits on enhancing physical, emotional, and spiritual wellbeing.
This book is a comprehensive reference on aromatic compounds present in essential oils and their therapeutic use. Starting from fundamentals of essential oil biosynthesis the book guides the reader through their basic biochemistry, toxicology, profiling, blending and clinical applications. The concluding chapters also present focused information about the therapeutic effects of essential oils on specific physiological systems, plant sources, skin treatment and cancer therapeutics.
The combination of basic and applied knowledge will provide readers with all the necessary information for understanding how to develop preclinical formulations and standard clinical therapies with essential oils. This is an essential reference for anyone interested in aromatherapy and the science of essential oils.
Adult mosquitoes require regular sugar meals, including nectar, to survive in natural habitats. Both males and females locate potential sugar sources using sensory proteins called odorant receptors (ORs) activated by plant volatiles to orient toward flowers or honeydew. The yellow fever mosquito, Aedes aegypti (Linnaeus, 1762), possesses a large gene family of ORs, many of which are likely to detect floral odors. In this study, we have uncovered ligand-receptor pairings for a suite of Aedes aegypti ORs using a panel of environmentally relevant, plant-derived volatile chemicals and a heterologous expression system. Our results support the hypothesis that these odors mediate sensory responses to floral odors in the mosquito’s central nervous system, thereby influencing appetitive or aversive behaviors. Further, these ORs are well conserved in other mosquitoes, suggesting they function similarly in diverse species. This information can be used to assess mosquito foraging behavior and develop novel control strategies, especially those that incorporate mosquito bait-and-kill technologies.
After mating, female mosquitoes need a blood meal to promote the reproductive process. When mosquitoes bite infected people and animals, they become infected with germs such as viruses and parasites. Mosquitoes rely on many cues for host selection and localization, among which the trace chemical cues emitted by the host into the environment are considered to be the most important, and the sense of smell is the main way to perceive these trace chemical cues. However, the current understanding of the olfactory mechanism is not enough to meet the needs of mosquito control. Unlike previous studies that focused on the olfactory receptor recognition spectrum to reveal the olfactory mechanism of mosquito host localization. In this paper, based on the observation that mosquitoes with incomplete antennae still can locate the host and complete blood feeding in the laboratory, we proposed that there may be some protection or compensation mechanism in the 13 segments of antennae flagella, and only when the antennae are missing to a certain threshold will it affect the mosquito's ability to locate the host. Through rational-designed behavioral experiments, we found that the 6th and 7th flagellomeres on the Aedes albopictus antenna are important in the olfactory detection of host searching. This study preliminarily screened antennal segments important for host localization of Ae. albopictus, and provided a reference for subsequent cell biology and molecular biology studies on these segments. Meanwhile, the morphology and distribution of sensilla on each antenna flagellomere were also analyzed and discussed in this paper.
Volatile organic compounds (VOCs) are gaseous chemicals found in ambient air and exhaled breath. In particular, highly reactive aldehydes are frequently found in polluted air and have been linked to various diseases. Thus, extensive studies have been carried out to elucidate disease-specific aldehydes released from the body to develop potential biomarkers for diagnostic purposes. Mammals possess innate sensory systems, such as receptors and ion channels, to detect these VOCs and maintain physiological homeostasis. Recently, electronic biosensors such as the electronic nose have been developed for disease diagnosis. This review aims to present an overview of natural sensory receptors that can detect reactive aldehydes, as well as electronic noses that have the potential to diagnose certain diseases. In this regard, this review focuses on eight aldehydes that are well-defined as biomarkers in human health and disease. It offers insights into the biological aspects and technological advances in detecting aldehyde-containing VOCs. Therefore, this review will aid in understanding the role of aldehyde-containing VOCs in human health and disease and the technological advances for improved diagnosis.
Chris Peterson and Joel Coats from the Department of Entomology at Iowa State University, USA, review the history of insect repellents from the 1920s down to recent work on plant-derived repellents.
Lactic acid, carbon dioxide and human sweat stimuli were presented singly and in combination to female Aedes aegypti (Linnaeus) within a wind-tunnel system. The take-off, flight, landing and probing responses of the mosquitoes were recorded using direct observation and video techniques. The analyses determined the nature of the response to different stimuli and the concentration ranges within which specific behaviours occurred. A threshold carbon dioxide concentration for taking-off of approximately 0.03% above ambient was detected. Lactic acid and human sweat samples did not elicit take-off when presented alone, however, when they were combined with elevated carbon dioxide, take-off rate was enhanced in most of the combinations tested. Flight activity was positively correlated with carbon dioxide level and some evidence for synergism with lactic acid was found within a narrow window of blend concentrations. The factors eliciting landing were more subtle. There was a positive correlation between landing rate and carbon dioxide concentration. At the lowest carbon dioxide concentration tested, landing occurred only in the presence of lactic acid. Within a window of low to intermediate concentrations, landing rate was enhanced by this combination. At the highest carbon dioxide concentration, landing was however inhibited by the presence of lactic acid. The sweat extract elicited landings in the absence of elevated carbon dioxide. This indicated the presence of chemical stimuli, other than lactic acid, active in the short range. Probing occurred only at low carbon dioxide concentrations and there was no probing when lactic acid alone was tested. There was however probing in the presence of combined stimuli, the level of response seemed to be positively correlated with the ratio of carbon dioxide and lactic acid concentrations.
The responses of female Aedes aegypti (Linnaeus) to a variety of stimuli were studied using an olfactometer bioassay. Mosquitoes responded significantly to convection currents produced by a human hand. The addition of water vapour to convection currents enhanced significantly the mosquitoes' response. Lactic acid, either alone or in combination with water vapour or/and convection currents however, did not increase the response level. Sweat extract elicited higher response than convection currents, water vapour and lactic acid. Human hands elicited significantly higher responses than any other stimuli. The presence of active chemicals other than lactic acid in human odour extract is discussed.
Behavioural responses of Aedes aegypti mosquitoes to ammonia were investigated in a modified Y-tube olfactometer. Ammonia was attractive in concentrations from 17 ppb to 17 ppm in air when presented together with lactic acid. Aqueous solutions of ammonia salts in concentrations comparable to those found in human sweat also increased the attractiveness of lactic acid. The role of lactic acid as an essential synergist for ammonia became further apparent by the fact that ammonia alone or in combination with carbon dioxide was not effective, even though the synergistic effect of carbon dioxide and lactic acid was corroborated. An extract from human skin residues, which attracts ~80% of the tested mosquitoes, contains both lactic acid and ammonia. The combination of these compounds, however, attracts no more than 45%, indicating that other components on human skin also play a role in host finding. Preparative liquid chromatography of the skin extract yielded three behaviourally active fractions which work together synergistically. Fraction III contains lactic acid as the effective principle; the compositions of the other two have not been clarified yet. The attractiveness of fraction I was augmented considerably when ammonia was added, whereas the effect of fraction II was not influenced by ammonia. These results suggests that ammonia is part of the effective principle of fraction II and contributes to the attractive effect of host odours.
In a behavioural study we have investigated the role of lactic acid for the host preferences of yellow fever mosquitoes (Aedes aegypti) by comparing the attractiveness of rubbings from the hands of different human individuals and extracts obtained from skin rubbings from different mammals (Bos primigenius f. taurus, Capra aegagrus f. hircus, Felis silvestris f. catus and Homo sapiens). Certain human individuals were consistently more attractive to mosquitoes than others. Addition of lactic acid markedly increased the degree of attractiveness of formerly less attractive human odour samples and they were preferred over those which were originally the most attractive. There was almost no response to animal odour samples. In contrast to human samples, which contain a high amount of lactate, this compound could not be detected in samples from animals. When skin emanations from animals were combined with lactic acid, however, as many mosquitoes responded to odour samples of B. primigenius f. taurus and C. aegagrus f. hircus as did to human odours. All these data demonstrate that olfactory-based host preference of the anthropophilic mosquito A. aegypti is to a large extent due to differences in the amount of lactic acid in the odour samples.
Extracellular recordings of the spike discharge patterns of single chemoreceptor neurons in the antennae of male Aedes aegypti mosquitos were obtained and compared with similar recordings made from homologous sensilla on the antennae of female A. aegypti. In both male and female mosquitos, the grooved-peg sensilla were associated with two types of neurons sensitive to lactic acid—one excited by lactic acid and the other one inhibited by lactic acid. The short, blunt-tipped sensilla trichodea Type II (A2-II) of the male mosquito house chemosensory neurons sensitive to volatile chemical substances associated with sources of plant nectar, whereas in the female this information is provided by the long, sharp-tipped sensilla trichodea and the female A2-II sensilla respond to oviposition-site attractants.
Catnip (nepetalactone) is closely related chemically to certain cyclopentanoid monoterpenes recently isolated from insects,
and it shares with some of these terpenes an ability to repel insects. It is suggested that the adaptive function of catnip
is to protect the plants that produce it against phytophagous insects.
All-night catches in 32 radially arranged ramp traps were compared for evidence of wind-influenced flight orientation and to investigate the range at which various Florida mosquitoes respond to air-borne host stimuli. Culex nigripalpus displayed strong upwind orientation both with and without animal bait, while the flight pattern of Culex pilosus was scarcely influenced by wind direction. Species showing a positive response to the multiple hosts exposed appeared to begin orienting toward the bait about 15 m away and the response increased the nearer they approached, i.e., at 10 and 5 m.
The attractiveness, to mosquitoes, of human subjects breathing normally and wearing a breathing apparatus which removed 95·5% of expired carbon dioxide were compared in the field. Significantly fewer mosquitoes approached the subject with a reduced carbon-dioxide output. Species differences were apparent in the degree of reduction of mosquitoes at the bait, as measured by the ratio of numbers attracted to subjects without and with the breathing apparatus. From the results of trials in the Gambia, West Africa, this ratio gave values of 0·67 for Mansonioides spp., 0·46 for Anopheles gambiae Giles/A. melas Theo. and 0·19 for Culex thalassius Theo., while complementary work in southern England gave a value of 0·34 for Aedes cantans (Mg.)/Ae. annulipes (Mg.). A reduced carbon-dioxide output had no effect on the proportion of mosquitoes attempting to feed once within close range of the host. These findings confirm that carbon dioxide is a long- or medium-range attractant.(Received May 08 1970)