Repellent Odors Research Articles

Termites can learn

It is generally believed that termites can’t learn and are not “intelligent”. This study aimed to test whether termites could have any form of memory. A Y-shaped test device with one release chamber and two identical test chambers was designed and constructed by 3D printing. A colony of damp wood termites was harvested from the wild. Worker termites were randomly selected for experiment. Repellent odors that could mimic the alarm pheromone for termites were first identified. Among all substances tested, a tea tree oil and lemon juice were found to contain repellent odors for the tested termites, as they significantly reduced the time that termites spent in the chamber treated with these substances. As control, a trail pheromone was found to be attractive. Subsequently, a second cohort of termites were operant conditioned by punishment using both tea tree oil and lemon juice, and then tested for their ability to remember the path that could lead to the repellant odors. The test device was thoroughly cleaned between trials. It was found that conditioned termites displayed a reduced tendency to choose the path that led to expectant punishment as compared with naïve termites. Thus, it is concluded that damp wood termites are capable of learning and forming “fear memory”, indicative of “intelligence” in termites. This result challenges established presumption about termites’ intelligence.

Cattle-Derived Unsaturated Aldehydes Repel Biting Midges and Mosquitoes

Host-derived repellents offer a novel way to reduce disease vector–host interactions, particularly for vectors and nuisance pests where commercial repellents are not available, e.g., Culicoides biting midges. By revising the criteria previously used to identify bioactive volatile organic compounds for Culicoides nubeculosus, we identify (E)-2-hexenal, (E)-2-heptenal, (E)-2-octenal, and (E)-2-nonenal to be differentially present in the headspace odour of cattle hair and to elicit antennal responses in this research model species. A blend of these unsaturated aldehydes elicited an aversive response in C. nubeculosus, as well as a repellent response in three disease vector mosquito species, Aedes aegypti, Culex quinquefasciatus and Anopheles coluzzii, a response that was stronger than that to the commercially available repellents tested (DEET, IR3535, PMD, icaridin, and d-allethrin). Culicoides nubeculosus was behaviourally indifferent to these commercially available repellents tested, except d-allethrin to which it was attracted. The identification of a host-derived repellent odour blend, which reduces the interaction between biting midges extends the array of tools to be used in integrated vector management of these and other disease vectors.

Cellular and Molecular Targets of Waterbuck Repellent Blend Odors in Antennae of Glossina fuscipes fuscipes Newstead, 1910.

Insects that transmit many of the world’s deadliest animal diseases, for instance trypanosomosis, find their suitable hosts and avoid non-preferred hosts mostly through olfactory cues. The waterbuck repellent blend (WRB) comprising geranylacetone, guaiacol, pentanoic acid, and δ-octalactone derived from waterbuck skin odor is a repellent to some savannah-adapted tsetse flies and reduces trap catches of riverine species. However, the cellular and molecular mechanisms associated with detection and coding of the repellent odors remain to be elucidated. Here, we demonstrated that WRB inhibited blood feeding in both Glossina pallidipes Austen, 1903 and Glossina fuscipes fuscipes Newstead, 1910. Using the DREAM (Deorphanization of Receptors based on Expression Alterations in odorant receptor mRNA levels) technique, combined with ortholog comparison and molecular docking, we predicted the putative odorant receptors (ORs) for the WRB in G. f. fuscipes, a non-model insect. We show that exposure of G. f. fuscipes in vivo to WRB odorant resulted in up- and downregulation of mRNA transcript of several ORs. The WRB component with strong feeding inhibition altered mRNA transcript differently as compared to an attractant odor, showing these two odors of opposing valence already segregate at the cellular and molecular levels. Furthermore, molecular dynamics simulations demonstrated that the predicted ligand–OR binding pockets consisted mostly of hydrophobic residues with a few hydrogen bonds but a stable interaction. Finally, our electrophysiological response showed the olfactory sensory neurons of G. f. fuscipes tuned to the tsetse repellent components in different sensitivity and selectivity.

Scaling the interactive effects of attractive and repellent odours for insect search behaviour

Insects searching for resources are exposed to a complexity of mixed odours, often involving both attractant and repellent substances. Understanding how insects respond to this complexity of cues is crucial for understanding consumer-resource interactions, but also to develop novel tools to control harmful pests. To advance our understanding of insect responses to combinations of attractive and repellent odours, we formulated three qualitative hypotheses; the response-ratio hypothesis, the repellent-threshold hypothesis and the odour-modulation hypothesis. The hypotheses were tested by exposing Drosophila melanogaster in a wind tunnel to combinations of vinegar as attractant and four known repellents; benzaldehyde, 1-octen-3-ol, geosmin and phenol. The responses to benzaldehyde, 1-octen-3-ol and geosmin provided support for the response-ratio hypothesis, which assumes that the behavioural response depends on the ratio between attractants and repellents. The response to phenol, rather supported the repellent-threshold hypothesis, where aversion only occurs above a threshold concentration of the repellent due to overshadowing of the attractant. We hypothesize that the different responses may be connected to the localization of receptors, as receptors detecting phenol are located on the maxillary palps whereas receptors detecting the other odorants are located on the antennae.

Commonly Used Insect Repellents Hide Human Odors from Anopheles Mosquitoes.

The mode of action for most mosquito repellents is unknown. This is primarily due to the difficulty in monitoring how the mosquito olfactory system responds to repellent odors. Here, we used the Q-system of binary expression to enable activity-dependent Ca2+ imaging in olfactory neurons of the African malaria mosquito Anopheles coluzzii. This system allows neuronal responses to common insect repellents to be directly visualized in living mosquitoes from all olfactory organs, including the antenna. The synthetic repellents N,N-diethyl-meta-toluamide (DEET) and IR3535 did not activate Anopheles odorant receptor co-receptor (Orco)-expressing olfactory receptor neurons (ORNs) at any concentration, and picaridin weakly activated ORNs only at high concentrations. In contrast, natural repellents (i.e. lemongrass oil and eugenol) strongly activated small numbers of ORNs in the Anopheles mosquito antennae at low concentrations. We determined that DEET, IR3535, and picaridin decrease the response of Orco-expressing ORNs when these repellents are physically mixed with activating human-derived odorants. We present evidence that synthetic repellents may primarily exert their olfactory mode of action by decreasing the amount of volatile odorants reaching ORNs. These results suggest that synthetic repellents disruptively change the chemical profile of host scent signatures on the skin surface, rendering humans invisible to Anopheles mosquitoes.

The taste system in fishes and the effects of environmental variables

The adaptability of the taste system in fish has led to a large variety in taste bud morphology, abundance and distribution, as well as in taste physiology characteristics in closely related species with different modes of life and feeding ecology. However, the modifications evoked in the sense of taste, or gustation, particularly during ontogeny when fishes are subject to different environmental variables, remain poorly studied. This review paper focusses on current knowledge to show how plastic and resistant the taste system in fishes is to various external factors, linked to other sensory inputs and shifts in physiological state of individuals. Ambient water temperature is fundamental to many aspects of fish biology and taste preferences are stable to many substances, however, the taste-cell turnover rate strongly depends on water temperature. Taste preferences are stable within water salinity, which gives rise to the possibility that the taste system in anadromous and catadromous fishes will only change minimally after their migration to a new environment. Food-taste selectivity is linked to fish diet and to individual feeding experience as well as the motivation to feed evoked by attractive (water extracts of food) and repellent (alarm pheromone) odours. In contrast, starvation leads to loss of aversion to many deterrent substances, which explains the consumption by starving fishes of new objects, previously refused or just occasionally consumed. Food hardness can significantly modify the final feeding decision to swallow or to reject a grasped and highly palatable food item. Heavy metals, detergents, aromatic hydrocarbons and other water contaminants have the strongest and quickest negative effects on structure and function of taste system in fish and depress taste perception and ability of fishes to respond adequately to taste stimuli after short exposures. Owing to phenotypic plasticity, the taste system can proliferate and partially restore the ability of fishes to respond to food odour after a complete loss of olfaction. In general, the taste system, especially its functionality, is regarded as stable over the life of a fish despite any alteration in their environment and such resistance is vital for maintaining physiological homeostasis.

Multiple modalities in insect warning displays have additive effects against wild avian predators

Allocation to different components of defence has been suggested as an explanation for the existence of multiple aposematic morphs in a single population. We tested whether there are trade-offs between warning colouration and chemical defence or whether these have an additive effect when combined, using blue tits (Cyanistes caeruleus) as predators and the polymorphic wood tiger moth (Arctia plantaginis) as prey. We used artificial edible models (with and without the moths’ defensive fluids) with paper wings whose colour and pattern properties matched those of real moths. When the models were presented sans defensive fluids or when the fluids were presented without colour cues, we detected no differences in initial avoidance between the two morphs. However, when the colour and chemical cues were combined, differences emerged. White wings elicited higher latency to approach regardless of the defensive fluids applied on them. After approach, however, the defensive fluids of both morphs presented on moth models elicited higher latency to attack than a water control, hinting at a repellent odour. Fluids of white moths rendered lower amounts of prey eaten regardless of wing colour, while yellow moths’ fluids provoked the highest occurrence of beak wiping behaviour. Our findings highlight the importance of accounting for interactive effects between different signal modalities, as these can create patterns not detectable when examined in isolation. Understanding these interactions is vital to determine how different components of multimodal warning displays provide protection at different stages of a predation event and, potentially, how multiple morphs can co-occur in a population.Significance statementThere are many things that can stop a predator attacking a prey such as looking scary or smelling bad, but if a predator does take a bite, tasting bad can make the difference between life and death for the prey. When combined with bright conspicuous colours, both repellent odours and deterrent tastes (i.e. chemical defences) can help predators learn to avoid unprofitable prey. However, it is unclear whether it is really the sum of these visual and chemical signals that most effectively deters predators or whether one is more important than the other. Examining the effects of warning colour and chemical defence in white and yellow wood tiger moths on wild-caught birds, we show that neither aspect of the moths’ defence in isolation is as effective for predator deterrence as the sum of both.

A Wind Tunnel for Odor Mediated Insect Behavioural Assays.

Olfaction is the most important sensory mechanism by which many insects interact with their environment and a wind tunnel is an excellent tool to study insect chemical ecology. Insects can locate point sources in a three-dimensional environment through the sensory interaction and sophisticated behavior. The quantification of this behavior is a key element in the development of new tools for pest control and decision support. A wind tunnel with a suitable flight section with laminar air flow, visual cues for in-flight feedback and a variety of options for the application of odors can be used to measure complex behaviour which subsequently may allow the identification of attractive or repellent odors, insect flight characteristics, visual-odor interactions and interactions between attractants and odors lingering as background odors in the environment. A wind tunnel holds the advantage of studying the odor mediated behavioural repertoire of an insect in a laboratory setting. Behavioural measures in a controlled setting provide the link between the insect physiology and field application. A wind tunnel must be a flexible tool and should easily support the changes to setup and hardware to fit different research questions. The major disadvantage to the wind tunnel setup described here, is the clean odor background which necessitates special attention when developing a synthetic volatile blend for field application.

Repellent activity of plants from the genus Chenopodium to Ostrinia nubilalis larvae

The olfactory choices expressed by naïve neonate European corn borer (ECB) larvae were tested by recording their locomotor activities in response to odours coming from plants of the genus Chenopodium (producing phytoecdysteroids or not). ECB larvae were found to be repelled from phytoecdysteroid-positive species, except C. album and C. polyspermum. On the contrary, they were mildly attracted or mildly repelled by phytoecdysteroid-negative species, except C. botrys (which emits a rancid odour). These observations indicate that neonate ECB larvae clearly differentiate plant odours and suggest that well-defended plants may emit repellent odours.

AN INNOVATED OF AN AIRFLOW OLFACTOMETER FOR MEASURING RESPONSE OF THE MEDITERRANEAN FRUIT FLY, CERATITIS CAPITATA (WEID.) TO ODORS

the present work was carried out to describe a new innovation of a simple detachable olfactometer for measuring the olfactory responses of fruit flies to different odors. Such device may be useful to discover the efficiency of current attractive or repellent odors or new odors that could be used for controlling fruit flies in fields. It could save effort, time and money required to investigate any new attractive or repellent material prior usage in the field Many experiments were conducted to standardize this device using the standard attractive material Buminal . These trials included determination of optimum concentration of test odor, optimum dose to test, velocity of air flow inside device, optimum number of flies that could be used in every test, optimum light intensity, best exposure time to test material and relationship between response of flies to test odor and temperature.

Responses of Glossina pallidipes and Glossina morsitans morsitans tsetse flies to analogues of δ-octalactone and selected blends

Previous studies have shown that δ-octalactone is an important component of the tsetse-refractory waterbuck (Kobus defassa) repellent odour blend. In the present study, structure-activity comparison was undertaken to determine the effects of the length of the side chain and ring size of the lactone on adult Glossina pallidipes and Glossina morsitans morsitans. The responses of the flies to each compound were studied in a two-choice wind tunnel. Increasing the chain length from C3 (δ-octalactone) to C4 (δ-nonalactone) enhanced repellency to both species (G. pallidipes from 60.0 to 72.0%, and G. m. morsitans from 61.3 to 72.6%), while increasing the ring size from six (δ-octalactone) to seven members (ε-nonalactone) changed the activity from repellency to attraction that was comparable to that of the phenolic blend associated with fermented cow urine (p>0.05). Blending δ-nonalactone with 4-methylguaiacol (known tsetse repellent) significantly (p<0.05) raised repellency to 86.7 and 91.7% against G. pallidipes and G. m. morsitans respectively. Follow-up Latin Square Designed field studies (Shimba hills in coastal areas in Kenya) with G. pallidipes populations confirmed the higher repellence of δ-nonalactone (with/without 4-methylguaiacol) compared to δ-octalactone (also, with/without 4-methylguaiacol). The results show that subtle structural changes of olfactory signals can significantly change their interactions with olfactory receptor neurons, and either shift their potency, or change their activity from repellence to attraction. Our results also lay down useful groundwork in the development of more effective control of tsetse by ‘push’, ‘pull’ and ‘push-pull’ tsetse control tactics.

Herbal Repellents against Agricultural Rodent Pest Species

Author(s): Hansen, Sabine C.; Jacob, Jens | Abstract: Field rodents such as common voles cause significant pre-harvest damage during population outbreaks in European agriculture, and commensal rodents such as house mice are of concern worldwide. Usually, rodenticides are applied to minimize damage by these species. Rodenticides are not species-specific and may cause environmental problems. Plant secondary metabolites (PSM) could be used as a tool for sustainable rodent control, potentially minimizing damage and environmental risk. We screened volatile PSMs in feeding trials and in enclosure trials to identify if the odor of herbal substances repelled the target species. In feeding trials, the odor of two PSMs considerably reduced food intake in both rodent species. The use of underground chambers in enclosures indicated three repellent odors were effective for house mice, based on visitation rates of these rodents. Common voles visited the chambers equally independent of treatment and hence showed no avoiding behaviour. Further PSMs, combinations, and varying concentrations will be screened to support development of products. Effective repellents could be used to treat commodities to be protected from rodents and to develop an “odor barrier” against common voles to reduce migration from refuge areas to crops. Our preliminary findings suggest species-specific effects of some PSMs (impact on common voles but not on house mice, and vice versa); this may offer an option to repel unwanted species. Our results contribute to the development of non-lethal management tools for rodent pest species that are potentially more target-specific than traps or rodenticides.

Application of a putative alarm cue hastens the arrival of invasive sea lamprey (Petromyzon marinus) at a trapping location

The sea lamprey Petromyzon marinus is an invasive pest in the Laurentian Great Lakes basin, threatening the persistence of important commercial and recreational fisheries. There is substantial interest in developing effective trapping practices via the application of behavior-modifying semiochemicals (odors). Here we report on the effectiveness of utilizing repellent and attractant odors in a push–pull configuration, commonly employed to tackle invertebrate pests, to improve trapping efficacy at permanent barriers to sea lamprey migration. When a half-stream channel was activated by a naturally derived repellent odor (a putative alarm cue), we found that sea lamprey located a trap entrance significantly faster than when no odor was present as a result of their redistribution within the stream. The presence of a partial sex pheromone, acting as an attractant within the trap, was not found to further decrease the time to when sea lamprey located a trap entrance relative to when the alarm cue alone was applied. Neither the application of alarm cue singly nor alarm cue and partial sex pheromone in combination was found to improve the numbers of sea lamprey captured in the trap versus when no odor was present — likely because nominal capture rate during control trials was unusually high during the study period. Behavioural guidance using these odors has the potential to both improve control of invasive non-native sea lamprey in the Great Lakes as well as improving the efficiency of fish passage devices used in the restoration of threatened lamprey species elsewhere.

Prior Exposure to DEET Interrupts Positive and Negative Responses to Olfactory Cues in Drosophila Melanogaster

While the high efficiency of N,N-diethyl-meta-toluamide (DEET) in protecting humans against disease-transmitting arthropods is unquestioned, the mode of action of DEET on a physiological and behavioural level remains debated. Recent advances demonstrated that DEET modulates the function of the insects’ odorant receptor complex. In this study we aimed to evaluate how DEET affects the behaviour of insects towards attractive and repellent odours. In a series of experiments with larvae and adults of the fruitfly Drosophila melanogaster, we were able to provide the first evidence that DEET, applied in a gaseous phase, interrupts not only positive but also negative responses to olfactory cues indicating that insects treated with DEET lose the ability to perceive and respond to odours. This effect was also observed if insects were exposed to DEET prior to but not during the behavioural experiments, but was reversible after some time. DEET functioned as deterrent in experiments where insects had direct contact to the substance. This dual function – the camouflage of hosts from a distance and the deterrence upon contact – may be the key for the high efficiency of DEET.

Nuclear PKG localization is regulated by Go alpha and is necessary in the AWB neurons to mediate avoidance in Caenorhabditis elegans

Neural circuits interpret sensory information from their environment and use this information to influence behavioral outputs. In Caenorhabditis elegans two bilaterally symmetric cephalic amphid organs each contain the ciliated termini of twelve classes of sensory neurons. Two of these sensory neuron pairs are called the AWB and the AWC neurons. The AWC neurons confer an ability to detect attractive volatile odors such as benzaldehyde, whereas the AWB neurons endow the animal with an ability to detect repulsive volatile odors such as 2-nonanone. Previously, it has been shown that transient nuclear localization of a Protein Kinase G (PKG) called EGL-4 in the AWC neuron facilitates adaptation after sustained odor input, and here we show that constitutively nuclear EGL-4 is required in the AWB neurons for the detection of repellent odors. Furthermore, we show that the Go alpha subunit protein GOA-1 regulates the nuclear localization of EGL-4 in both AWB and AWC neurons. These data reveal novel insight into how the localization of an individual kinase can form a turnout switch to modify output in different neurons to drive opposite sensory behaviors.

Erratum: A high-throughput behavioral paradigm for Drosophila olfaction - The Flywalk

How can odor-guided behavior of numerous individual Drosophila be assessed automatically with high temporal resolution? For this purpose we introduce the automatic integrated tracking and odor-delivery system Flywalk. In fifteen aligned small wind tunnels individual flies are exposed to repeated odor pulses, well defined in concentration and timing. The flies' positions are visually tracked, which allows quantification of the odor-evoked walking behavior with high temporal resolution of up to 100 ms. As a demonstration of Flywalk we show that the flies' behavior is odorant-specific; attractive odors elicit directed upwind movements, while repellent odors evoke decreased activity, followed by downwind movements. These changes in behavior differ between sexes. Furthermore our findings show that flies can evaluate the sex of a conspecific and males can determine a female's mating status based on olfactory cues. Consequently, Flywalk allows automatic screening of individual flies for their olfactory preference and sensitivity.

Odour-Mediated Orientation of Beetles Is Influenced by Age, Sex and Morph

The behaviour of insects is dictated by a combination of factors and may vary considerably between individuals, but small insects are often considered en masse and thus these differences can be overlooked. For example, the cowpea bruchid Callosobruchus maculatus F. exists naturally in two adult forms: the active (flight) form for dispersal, and the inactive (flightless), more fecund but shorter-lived form. Given that these morphs show dissimilar biology, it is possible that they differ in odour-mediated orientation and yet studies of this species frequently neglect to distinguish morph type, or are carried out only on the inactive morph. Along with sex and age of individual, adult morph could be an important variable determining the biology of this and similar species, informing studies on evolution, ecology and pest management. We used an olfactometer with motion-tracking to investigate whether the olfactory behaviour and orientation of C. maculatus towards infested and uninfested cowpeas and a plant-derived repellent compound, methyl salicylate, differed between morphs or sexes. We found significant differences between the behaviour of male and female beetles and beetles of different ages, as well as interactive effects of sex, morph and age, in response to both host and repellent odours. This study demonstrates that behavioural experiments on insects should control for sex and age, while also considering differences between adult morphs where present in insect species. This finding has broad implications for fundamental entomological research, particularly when exploring the relationships between physiology, behaviour and evolutionary biology, and the application of crop protection strategies.

Host Specific Cephenemyia of Deer Repelled by Non-Host Odors

Females of Cephenemyia apicata and C. jellisoni made significantly fewer (P < 0.05) larvipositions on baited models of black-tailed deer paired with a camouflaged sheep than on similar models operated without a paired sheep. Models were baited with CO2 and 1-octen-3-ol. In the absence of natural sheep odors these host specific flies were attracted to and larviposited on sheep models baited with CO2 and octenol and to CO2-baited odorless models of cows and horses. These results indicate that odors associated with sheep repelled host-seeking Cephenemyia females from baited deer models. Under natural conditions repellent odors of non-host species may assist in maintaining host specificity of these Cephenemyia species and in flies not wasting time and energy responding to non-host odors.

A high-throughput behavioral paradigm for Drosophila olfaction - The Flywalk

How can odor-guided behavior of numerous individual Drosophila be assessed automatically with high temporal resolution? For this purpose we introduce the automatic integrated tracking and odor-delivery system Flywalk. In fifteen aligned small wind tunnels individual flies are exposed to repeated odor pulses, well defined in concentration and timing. The flies' positions are visually tracked, which allows quantification of the odor-evoked walking behavior with high temporal resolution of up to 100 ms. As a demonstration of Flywalk we show that the flies' behavior is odorant-specific; attractive odors elicit directed upwind movements, while repellent odors evoke decreased activity, followed by downwind movements. These changes in behavior differ between sexes. Furthermore our findings show that flies can evaluate the sex of a conspecific and males can determine a female's mating status based on olfactory cues. Consequently, Flywalk allows automatic screening of individual flies for their olfactory preference and sensitivity.

Identification of mosquito repellent odours from Ocimum forskolei

BackgroundNative mosquito repellent plants have a good potential for integrated mosquito control in local settings. Ocimum forskolei, Lamiaceae, is used in Eritrea as a spatial mosquito repellent inside houses, either through crushing fresh plants or burning dry plants. We verified whether active repellent compounds could be identified using gas-chromatography coupled electroantennogram recordings (GC-EAD) with headspace extracts of crushed plants.ResultsEAD active compounds included (R)-(-)-linalool, (S)-(+)-1-octen-3-ol, trans-caryophyllene, naphthalene, methyl salicylate, (R)-(-)-α-copaene, methyl cinnamate and (E)-ocimene. Of these compounds (R)-(-)-linalool, methyl cinnamate and methyl salicylate reduced landing of female Aedes aegypti on human skin-odor baited tubes. The latter two are novel mosquito repellent compounds.ConclusionsThe identification of mosquito repellent compounds contributes to deciphering the mechanisms underlying repulsion, supporting the rational design of novel repellents. The three mosquito repellent compounds identified in this study are structurally dissimilar, which may indicate involvement of different sensory neurons in repulsion. Repulsion may well be enhanced through combining different repellent plants (or their synthetic mimics), and can be a locally sustainable part in mosquito control efforts.