How do insects smell

Higher sensitivity may also be an advantage in environments where picking the signal is very difficult. Western African populations of Ficus sur are pollinated by two sister species of Agaonid fig wasps Kerdelhue et al.

Although roughly sympatric, these two species differ both in their habitat preferences and their antennal morphology. Ceratosolen silvestrianus , mostly found in open habitats where population density of F. On the contrary, C. Reciprocally, it is highly possible that insect community composition, especially the sensory abilities of the species composing that community as well as the identity of co-occurring plant species, influences the evolution of VPC emissions by plants and as a consequence the odorscape.

For instance, the influence of pollinator- or herbivore-mediated selection on the emission of VPCs by plants has already been shown in the context of pairwise plant-species interactions Becerra et al. In addition, divergent seasonal patterns of scent emission by flowers have been revealed in a Mediterranean plant-community in relation to pollinator seasonal abundance and local plant abundance Filella et al.

More specifically, this study shows that VPC emission is higher in plant species that bloom early in the flowering period when pollinators are rare relative to flowers than in species blooming later in the season when there is a surplus of pollinators relative to flowers. The authors hypothesize that inter-specific competition for pollinator attraction might explain this variation.

So far, due to the limited number of studies exploring the association between VPCs and plant-insect community structure, we have limited evidence of the effect of insect association on odorscape composition. Interestingly, a very recent study conducted at the community level pointed out an association between VPC chemical classes emitted by flowers and pollinator groups Kantsa et al.

In another study, behavioral responses of pollinator species to floral odors were found to explain a large part of the plant-pollinator network structure Junker et al. This recent use of network-based methods to explore the importance of chemical signals in the structuring of plant-insect community will probably open the path to new discoveries on the evolution of plant-insect chemical communication.

Manipulating the odorscapes of herbivorous pest species has already important practical implications in plant protection as an alternative to pesticides. Mating disruption methods use a synthetic sex pheromone to disturb the chemical communication between sexes. This interrupts normal mating behavior, thereby affecting chances of reproduction of pest insects.

Large cultivated areas are generally treated by mating disruption to prevent introgression of mated females Witzgall et al. Mating disruption is currently successfully used against numerous moth species in various types of crop plants, either in fields cotton, maize , orchards apple trees , vineyards, or even forests. Interestingly, this diversity of treated crop plants indicates that it is feasible to modify the odorscape in very different plant covers.

Modifying the odorscape implies to be able to release biologically active concentrations of odorants in the field at economically relevant costs. The success of mating disruption has promoted research for efficient dispenser technology, because the synthetic pheromone is often costly to produce. This development led, in less than 50 years, from the first hand-applied meso-dispensers to biodegradable, mechanically sprayable micro-formulations. A striking example of this development has been reviewed for the European grapevine moth, Lobesia botrana Hummel, Active dispensers releasing the pheromone as puffs of aerosol at night when moths are active have been experimented, for instance against Cydia pomonella McGhee et al.

The decrease in moth populations obtained with these dispensers demonstrates the feasibility of a very precise control of the odorscape by adjusting the emission rates and the temporal release pattern of odorants.

Still, the diffusion technology remains a bottleneck limiting the development of semiochemical uses in plant protection. Modifying the odorscape by introducing other plant species that naturally release different VPCs can also reduce the damage caused by pest insects. Non-host plants inter-cropped with host plants decreased the oviposition of Anthomyiid flies on the hosts Finch et al. To explain this phenomenon, it was proposed that females landed indifferently on the foliage of one or the other plant species, relying upon unspecific visual stimuli rather than on olfactory cues, but flew away from non-host plants without laying eggs because of the unsuitability of contact chemostimuli.

After several errors, they finally flew away from the mixed field, this behavior resulting in a statistical reduction of the number of successful ovipositions on hosts. However, the role of non-host volatiles in oviposition deterrence has been confirmed later. For instance, methyl salicylate released by birch trees has been identified as the main factor in the reduction of mating and number of processionary moth nests on pine trees surrounded by birch trees Jactel et al.

This phenomenon is exploited in push and pull strategies, in which a pest insect is repelled from a protected crop by a repellent plant while it is attracted by plants of lesser economic value to field edges where it can be destroyed Cook et al. The chemical complexity of plant volatilomes and insect olfactomes has been intensively investigated. A considerable amount of information is available regarding the identity of the volatiles mediating biotic interactions that involve insects.

But we need now to grasp the complexity of the dense information networks mediated by semiochemicals. A recent analysis of a pollination network at the landscape level shows that the composition and intensity of volatile floral emissions, among other floral traits, correlate to the level of specialization of each plant species, as well as to visitation rates by the different pollinator guilds Kantsa et al. It is striking to note that the level of complexity in their ecological role is highly variable among volatile compounds.

Some semiochemicals, like most of the pheromones, are involved in specialized and confidential communication. This multifunctionality and the interweaving of olfactory interactions are serious obstacles to decipher odorscape ecological functions at multitrophic levels.

It also makes it difficult to assess the impact of biotic factors the rise of an invasive species for instance , or abiotic factors like global warming or pollution on olfactory communication at ecosystem scale.

Using network analysis approaches in order to study how the information flows within ecosystems should overcome the apparent intricacy of odorscapes. The ecological relevance of the concept of odorscape is stressed by the growing body of evidence indicating that the olfactory environment and other contextual information do influence the way insects respond to specific signals.

Indeed, insect odorscapes are essentially multidimensional, including not only chemical identities, but also physical and temporal parameters, plus sensory, perceptual, and cognitive features.

Adapting their responses to the context becomes particularly important to insects when the signal itself is ambiguous. This partly explains why insects may reliably respond to ubiquitous plant volatiles in complex olfactory scenes mixing VPCs from host and non-host plants Meiners, Context dependence is also particularly important to consider when developing infochemicals to be applied in plant protection. Studying single odor signals is useful in gaining knowledge about the ecological function of these signals.

But in the end, we need to consider the signals within their context in order to fully understand how infochemical networks function at the ecosystem level. Since odorscapes are key elements of ecosystem functioning, it becomes essential to evaluate the impact of atmospheric pollution and climate change on their evolution.

There are indications that air pollution affects interactions between plants and insects beneficial to agriculture with potential consequences on plant productivity Girling et al. We need to better investigate the biological effects of atmospheric VPC reaction products on insect and plant communication Simpraga et al.

It is well established that plants modify their volatile emissions in response to biotic or abiotic stresses. Since plant metabolism responses are relatively fast compared to occurrence of visible damage, monitoring of induced VPCs could provide early alerts and allow for fast and timely implementation of remediation solutions.

More studies are urgently needed, first to describe present odorscapes in a diversity of ecosystems, then to follow their evolution and evaluate how it affects the ecosystem functioning. Monitoring the odorscape composition could also serve as a reliable indicator of ecosystem quality and of biodiversity levels, a major concern in times of diminution of insect populations Dirzo et al.

Global change is expected to have a profound impact on ecosystems, including VPC emissions and transport Figure 1. Current knowledge on the impact of CO 2 and temperature on plant physiology suggests a global increase in VPC emission rates as a result of climate change Holopainen et al.

How will insects respond to the resulting alterations in odorscape concentration, composition, and structure? While it is clear that OR tuning adapts to the characteristics of the signal to be detected, studies showing how the insect olfactory system adapts to specific olfactory environments, be it via OR tuning or antennal morphology, are needed.

A combination of molecular and neuroethological methods, applied to proper models and with a sound ecological background, will allow to gain a deeper understanding of the mechanisms involved in the insect adaptation to changing environments. Achieving this goal will require a proper description of olfactory landscapes, which depends on our capacity to isolate and identify the diverse volatile organic compounds that occur often in very small concentrations.

Improvements in analytical techniques have made VPCs some of the best studied plant metabolites. The most universal detector, the flame ionization detector is stable, linear, and offers minimum detectable amounts in the order of 0. To bring detection limits further down, sample enrichment by dynamic head space collections on porous polymer sorbents is often used to the detriment of the temporal resolution. Yet, in natural conditions, transport of the odorant molecules by air profoundly reshapes the stimulus both spatially and temporally.

The aerial concentration of VPCs undergoes considerable variation over time. It is essential to monitor this variation in order to properly describe natural odorscapes.

Proton transfer reaction-mass spectrometry allows real-time trace gas monitoring at the pptv level. However, it cannot discriminate different compounds within one nominal mass, a serious limit to the apprehension of odorscape complexity. Fortunately, increasingly miniaturized set-ups combining fast trapping with fast online GC analysis and sensitivity in the ppbv range have facilitated remote field analyses.

While these technical advances have created opportunities for detailed views on the time courses of VPC emissions, describing the fine temporal and spatial structure of odorscapes remains a complicated task and we still have very little insight into how it might vary across habitat types. One more argument to the necessity of studying the physics of the odorscape is the fact that notable differences between the atmospheric conditions prevailing between diurnal and nocturnal environments might have contributed to the success of olfactory communication in nocturnal insects.

For instance, the lower wind, turbulence, and oxidant levels that prevail at night might facilitate the persistence of chemical trails over longer distances, and lower background VPC emissions might lead to lower olfactory noise, potentially making olfaction more reliable at night, and the cost-benefit balance for maintaining large olfactory organs more favorable Elgar et al.

Finally, progresses in odorscape characterization will open the path to many more agronomic applications. Mating disruption, a method based on the manipulation of one critical component of moth odorscape at field scale, has offered a successful substitute to pesticides in the control of major lepidopteran pest species.

At close range, repellent molecules are used to deterring hematophagous or parasite insects. Essential oil fumigations are used to eliminate pests of stored goods, but the concentrations in treated premises reach values 10 6 times stronger than their concentrations in a natural odorscape. The huge diversity of components of essential oils provides a big reservoir of potential semiochemicals to control insects Mossa, However, the diffusion in the field of adapted aerial concentrations of costly bioactive odorants, with different volatilities, is still a serious limitation to odorscape manipulation.

New formulation technologies, which include VOCs in sprayable and biodegradable nanocapsules, will resolve many technical problems posed by field application. Besides these purely technical solutions, one might prefer natural release, for instance by plant varieties selected for their specific VPC emissions.

This option will also offer the advantage of more natural solutions in agroecology. All authors contributed to analyze the literature and write the manuscript. MR coordinated the project. The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Ache, B. Mechanisms for mixture suppression in olfactory receptors of the spiny lobster. Senses 13, — Ainsworth, E. Understanding and improving global crop response to ozone pollution. Plant J. Anderson, P. Experience-based modulation of behavioural responses to plant volatiles and other sensory cues in insect herbivores. Plant Cell Environ. Andersson, M.

Mechanisms of odor coding in coniferous bark beetles: from neuron to behavior and application. Peripheral modulation of pheromone response by inhibitory host compound in a beetle.

Insect olfaction and the evolution of receptor tuning. Arimura, G. Effects of feeding Spodoptera littoralis on lima bean leaves: IV. Diurnal and nocturnal damage differentially initiate plant volatile emission. Plant Physiol. Atema, J. Eddy chemotaxis and odor landscapes: exploration of nature with animal sensors. Atkinson, R. Gas-phase tropospheric chemistry of biogenic volatile organic compounds: a review. Bachy, A. Are BVOC exchanges in agricultural ecosystems overestimated? Insights from fluxes measured in a maize field over a whole growing season.

Badeke, E. A challenge for a male noctuid moth? Discerning the female sex pheromone against the background of plant volatiles. Baker, T. Moth uses fine tuning for odour resolution. Nature Manoeuvres used by flying male oriental fruit moths to relocate a sex pheromone plume in an experimentally shifted wind-field.

Baldwin, I. Plant volatiles. Barrozo, R. Switching attraction to inhibition: mating-induced reversed role of sex pheromone in an insect.

Becerra, J. Macroevolutionary chemical escalation in an ancient plant-herbivore arms race. USA , — Bell, J. Behavior reveals selective summation and max pooling among olfactory processing channels. Neuron 91, — Berg, B. The significance of major pheromone components and interspecific signals as expressed by receptor neurons in the oriental tobacco budworm moth, Helicoverpa assulta. A , — Processing of pheromone information in related species of Heliothine moths. Insects 5, — Bergougnoux, M.

Exposure to thymol decreased phototactic behaviour in the honeybee Apis mellifera in laboratory conditions. Apidologie 44, 82— Beyaert, I. Relevance of resource-indicating key volatiles and habitat odour for insect orientation.

Bhandawat, V. Sensory processing in the Drosophila antennal lobe increases reliability and separability of ensemble odor representations. Bicchi, C. Methods in molecular biology. Google Scholar. Binyameen, M. Modulation of reproductive behaviors by non-host volatiles in the polyphagous Egyptian cotton leafworm, Spodoptera littoralis.

Borrero-Echeverry, F. Plant odor and sex pheromone are integral elements of specific mate recognition in an insect herbivore. Evolution 72, — Bruce, T. The first crop plant genetically engineered to release an insect pheromone for defence. Perception of plant volatile blends by herbivorous insects - finding the right mix.

Phytochemistry 72, — Insect host location: a volatile situation. Trends Plant Sci. Budick, S. Free-flight responses of Drosophila melanogaster to attractive odors. Buehlmann, C. Desert ants use olfactory scenes for navigation. Butterwick, J. Cryo-EM structure of the insect olfactory receptor Orco.

Nature , — Byers, J. Avoidance of nonhost plants by a bark beetle, Pityogenes bidentatus , in a forest of odors. Naturwiss 91, — Cape, J. Effects of airborne volatile organic compounds on plants. Lewis London: Academic Press , — Control of moth pests by mating disruption: successes and constraints. Navigational strategies used by insects to find distant, wind-borne sources of odor.

Carrasco, D. Insect host plant selection in complex environments. Insect Sci. Celani, A. Odor landscapes in turbulent environments.

Cha, D. Eavesdropping on plant volatiles by a specialist moth: significance of ratio and concentration. PloS One 6:e Chan, H. Odorant mixtures elicit less variable and faster responses than pure odorants. PLoS Comput. Conversano, T. Background odour may impair detection of chemical signals for social recognition. Austral Entomol. Cook, S. The use of push-pull strategies in integrated pest management. Functional evolution of Lepidoptera olfactory receptors revealed by deorphanization of a moth repertoire.

Degen, T. High genetic variability of herbivore-induced volatile emission within a broad range of maize inbred lines. Deisig, N. Neural representation of olfactory mixtures in the honeybee antennal lobe. Dekker, T. Olfactory shifts parallel superspecialism for toxic fruit in Drosophila melanogaste r sibling, D. Delory, B. Root-emitted volatile organic compounds: can they mediate belowground plant-plant interactions?

Plant Soil , 1— Den Otter, C. Chapman and E. Dicke, M. Plant phenotypic plasticity in the phytobiome: a volatile issue. Plant Biol. Dirzo, R. Defaunation in the Anthropocene.

Science , — Dugravot, S. Increased sulfur precursors and volatiles production by the leek Allium porrum in response to specialist insect attack. Consequences for a specialist insect and its parasitoid of the response of Allium porrum to conspecific herbivore attack.

Egea-Weiss, A. High precision of spike timing across olfactory receptor neurons allows rapid odor coding in Drosophila. Elgar, M. Insect antennal morphology: the evolution of diverse solutions to odorant perception. Yale J. PubMed Abstract Google Scholar. Elkinton, J. Pheromone puff trajectory and upwind flight of male gypsy moths in a forest. Molecules Insects are very smell-dependent which makes them prime candidates for studying how the sense of smell works and how it influences behavior.

Following the whole process from molecule detection and the reaction of the nerves to the outcome of behavior the researchers found a line in the fly's brain that identifies bad odors and leads the fly to avoid these smells as they indicate something is toxic.

Because the olfactory systems of all species work in a similar way, the findings can be used to draw conclusions to the human sense of smell. Publication Researcher Institution Beyond. Area of Research Evolutionary Neuroethology. Selected Publications. Hany K. Dweck, Shimaa A. Hansson and Marcus C.

Get Full Access Export. Ebrahim, Abu Farhan, Bill S. Ebrahim, Michael Thoma, Ahmed A. Mohamed, Ian W. Use precise geolocation data.

Select personalised content. Create a personalised content profile. Measure ad performance. Select basic ads. Create a personalised ads profile. Select personalised ads. Apply market research to generate audience insights. Measure content performance. Develop and improve products. List of Partners vendors. Share Flipboard Email. Debbie Hadley.

Entomology Expert. Science News. ScienceDaily, 9 January University Of California - Davis. Exposing Insects' Sense Of Smell. Retrieved November 8, from www. The predator insects that feed on these bugs emit odors that pests can sense, which changes the pests' behavior and