Blend Of Plant Volatiles Research Articles

Volatile Organic Compound Emissions in the Changing Arctic

Arctic ecosystems have long been thought to be minimal sources of volatile organic compounds (VOCs) to the atmosphere because of their low plant biomass and cold temperatures. However, these ecosystems experience rapid climatic warming that alters vegetation composition. Tundra vegetation VOC emissions have stronger temperature dependency than current emission models estimate. Thus, warming, both directly and indirectly (via vegetation changes) likely increases the release and alters the blend of emitted plant volatiles, such as isoprene, monoterpenes, and sesquiterpenes, from Arctic ecosystems. Climate change also increases the pressure of both background herbivory and insect outbreaks. The resulting leaf damage induces the production of volatile defense compounds, and warming amplifies this response. Soils function as both sources and sinks of VOCs, and thawing permafrost is a hotspot for soil VOC emissions, contributing to ecosystem emissions if the VOCs bypass microbial uptake. Overall, Arctic VOC emissions are likely to increase in the future with implications for ecological interactions and atmospheric composition.

Enhanced parasitisation of caterpillars and aphids on field‐grown Brassica oleracea plants upon soil amendment with insect exuviae

Abstract Multitrophic plant–insect interactions are mediated by plant volatiles. The emission of herbivore‐induced plant volatiles is influenced by environmental conditions, such as soil microbes and nutrient composition, with consequences for above‐ground trophic interactions. Here, we investigated whether insect exuviae in the soil alter the plant's volatile blend and attraction of parasitoids in the laboratory and whether this attraction also occurs in the field. We studied the effects of soil amendment with exuviae originating from three insect species, Tenebrio molitor, Acheta domesticus and Hermetia illucens, on the proportion of parasitised Plutella xylostella caterpillars and Brevicoryne brassicae aphids in the field in three consecutive years. In the laboratory, we collected and analysed the volatile blend of amended plants infested with caterpillars or aphids. The attraction of the parasitoids Diadegma semiclausum and Diaeretiella rapae, respectively, towards these volatile blends was assessed in an olfactometer. Our study shows that insect exuviae‐amended soil enhanced the proportion of parasitised herbivores of two species in the field. Relative amounts of several components of the plant volatile blend were affected by soil amendment. Soil amendment with Acheta domesticus or Tenebrio molitor exuviae resulted in an increased attraction of the two parasitoid species in the olfactometer. Soil amendment with insect exuviae altered the plant volatile blend leading to enhanced attraction of parasitoids in laboratory assays. These effects were sustained under the complex and variable biotic and abiotic conditions in the field. Our results underline the importance of belowground processes, such as the decomposition of insect exuviae, on aboveground volatile‐mediated multitrophic interactions. Read the free Plain Language Summary for this article on the Journal blog.

Identity Matters: Multiple Herbivory Induces Less Attractive or Repellent Coffee Plant Volatile Emission to Different Natural Enemies.

Co-infestations by herbivores, a common situation found in natural settings, can distinctly affect induced plant defenses compared to single infestations. Related tritrophic interactions might be affected through the emission of changed blends of herbivore-induced plant volatiles (HIPVs). In a previous study, we observed that the infestation by red spider mite (Oligonychus ilicis) on coffee plants facilitated the infestation by white mealybug (Planococcus minor), whereas the reverse sequence of infestation did not occur. Here, we examined the involvement of the jasmonate and salicylate pathways in the plant-mediated asymmetrical facilitation between red spider mites and white mealybugs as well as the effect of multiple herbivory on attractiveness to the predatory mite Euseius concordis and the ladybug Cryptolaemus montrouzieri. Both mite and mealybug herbivory led to the accumulation of JA-Ile, JA, and cis-OPDA in plants, although the catabolic reactions of JA-Ile were specifically regulated by each herbivore. Infestation by mites or mealybugs induced the release of novel volatiles by coffee plants, which selectively attracted their respective predators. Even though the co-infestation by mites and mealybugs resulted in a stronger accumulation of JA-Ile, JA and SA than the single infestation treatments, the volatile emission was similar to that of mite-infested or mealybug-infested plants. However, multiple infestation had a negative impact on the attractiveness of HIPVs to the predators, making them less attractive to the predatory mite and a repellent to the ladybug. We discuss the potential underlying mechanisms of the susceptibility induced by mites, and the effect of multiple infestation on each predator.

A meta-analytic investigation of the potential for plant volatiles and sex pheromones to enhance detection and management of Lepidopteran pests.

Effective early detection, monitoring and management methods are critical for reducing the impacts of insect pests in agriculture and forestry. Combining host plant volatiles with sex pheromones could enhance trapping methodologies, whilst the use of non-host volatiles could improve the effectiveness of pest management through repellency effects. In this meta-analysis approach, we analysed 51 studies that used electroantennograms (EAG), wind tunnels and/or field traps to evaluate the antennal and behavioural responses of Lepidoptera to sex pheromones combined with attractant or repellent plant volatiles. Proposed attractant plant volatiles had a positive association with female Lepidoptera responses to sex pheromone, but effects on males were highly variable, with unexpected repellency reported in some studies. Proposed repellent plant volatiles were significantly or near-significantly negatively associated with male attraction to sex pheromones but were scarcely studied. Sub-group analysis identified that male responses to sex pheromone were reduced when the dose of attractant plant volatile relative to sex pheromone was increased. Green-leaf volatiles were associated with the strongest positive effects for males in field traps. Multiple-compound attractant plant volatile blends were less effective than single compounds in field studies. Our analysis demonstrates, (i) the potential value of combining host plant volatiles with sex pheromones to capture females rather than only males, (ii) the importance of identifying appropriate host plant volatiles and optimal relative doses, and (iii) the potential for non-host plant volatile use in pest management strategies.

Review of the chemical ecology of homoterpenes in arthropod–plant interactions

AbstractThe homoterpenes 4,8‐dimethyl‐1,3,7‐nonatriene (DMNT) and 4,8,12‐trimethyl‐1,3,7,11‐tridecatetraene (TMTT) are volatile products of plant metabolism reported from diverse plant taxa and multiple plant tissues. As such, they have a range of potential ecological functions. Here, we review the key literature to assess evidence for roles in contrasting plant–arthropod interactions. TMTT, and DMNT especially, have been reported as sometimes dominant constituents of floral scents from angiosperm taxa ranging from primitive Magnoliales to more advanced, taxonomic orders of economic significance such as Fabales and Sapindales. Although all taxa producing TMTT and DMNT in floral scents are entomophilous (‘insect pollinated’), experimental evidence for an assumed role of these homoterpenes in pollinator attraction is limited. Representing a trade‐off, in some cases, homoterpenes in floral scents have been shown to act as kairomones, attracting herbivores. Additionally, both TMTT and DMNT are released by plant foliage in response to arthropod feeding, mechanical damage simulating feeding, or even egg deposition. Evidence for a functional role in herbivore‐induced plant volatile (HIPV) blends comes from a wide range of angiosperm orders, including anemophilous (‘wind pollinated’) taxa, as well as from gymnosperms. We conclude by considering how TMTT and DMNT function in community‐level interactions and highlighting research priorities that will reveal how plants avoid trade‐offs from contrasting ecological functions of DMNT and TMTT release and how homoterpene production might be exploited to develop improved crop varieties.

The Role of Green Gram Plant Volatile Blends in the Behavior of Arctiid Moth, Spilosoma obliqua.

This study investigated effects of volatile blends released from undamaged (UD), insect-damaged [ID, plants fed by larvae of Spilosoma obliqua Walker (Lepidoptera: Arctiidae)] and mechanically-damaged (MD) plants of three green gram cultivars [PDM 54, Pusa Baisakhi and Samrat] including synthetic blends on the behavior of conspecific adult moths in Y-tube olfactometer bioassays. Females showed attraction towards volatile blends of UD, ID and MD plants of these green gram cultivars against the control solvent (CH2Cl2). The components of volatile blends in UD plants of three green gram cultivars are not similar, but no any difference was found among three cultivars in term of the attractive effect on the insect moths when volatile blends from UD plants of these three cultivars were tested against one another. Females were more attracted towards volatile blends of ID plants of a particular cultivar compared to UD plants of the same cultivar. Total amount of volatiles was higher in ID plants than UD plants. Some herbivore-induced plant volatiles - (Z)-3-hexenal, 1-hexanol, (Z)-3-hexenyl acetate, 2-octanol and ocimene were attractive to the insect moths. Females were attracted towards three synthetic blends resembling amounts present in natural volatile blends of ID plants of these three cultivars in Y-tube olfactometer and wind tunnel bioassays, suggesting that involvement of host-specific chemical cues in long-range host location by S. obliqua females. If attraction of adult S. obliqua to these synthetic volatile blends is upheld by field trials then these blends may find practical application in detection and monitoring of S. obliqua populations.

Intraspecific plant variation and nonhost herbivores affect parasitoid host location behaviour

Parasitoids need to find their hosts in patchy environments that differ in profitability. To maximize foraging efficiency, parasitoids use volatile information of plants on which their hosts feed. The blend of plant volatiles emitted is affected by genetic variation in plants and by the herbivore species feeding on the plant. How parasitoids deal with variation in plant volatiles induced by host or nonhost herbivores on various plant genotypes in a plant stand is unclear. In a wind tunnel, we examined foraging behaviour of the parasitoid Cotesia glomerata in mixes of white cabbage cultivars with host ( Pieris brassicae ) and nonhost herbivores ( Mamestra brassicae or Delia radicum ). We specifically studied the efficiency of parasitoids in locating a host-infested plant when having to pass three other plants that varied in volatile emission by cultivar and herbivore identity. We show that foraging decisions of C. glomerata are affected by the apparency of volatile cues from upwind host-infested plants. We found that parasitoids flew over the first three plants more often when the last plant was a host-infested attractive cultivar and the first three plants were a less attractive cultivar, regardless of the presence of host or nonhost herbivores. Furthermore, parasitoids spent more time on the first three plants if these were infested with host or nonhost larvae, and this effect was stronger when the first three plants were of the attractive cultivar. Our results suggest that parasitoids may more easily locate host herbivores on plant genotypes with more apparent volatile information. However, host location efficiency is affected by the contrast with other plumes of plant volatiles derived from genotypic variation in plants and induction of volatiles by nonhost herbivores. Apparency of information on upwind patches influences patch residence time and patch choice and is an important component of optimal foraging in parasitoids. • Foraging decisions by Cotesia glomerata are affected by the apparency of information. • Profitability of upwind patches affects foraging decisions on the current patch. • Nonhost herbivores with traits similar to the host reduced host location efficiency. • Established parasitoid cultivar preferences are nuanced in complex plant mixtures.

Responses of Adult Hypera rumicis L. to Synthetic Plant Volatile Blends.

The behavioral responses of Hypera rumicis L. adults to varying blends of synthetic plant volatiles (SPVs) at various concentrations in lieu of single compounds are reported for the first time. For this study, Rumex confertus plants were treated with two blends of SPVs at different quantities that act as either attractants or repellents to insects. Blend 1 (B1) consisted of five green leaf volatiles (GLVs), namely (Z)-3-hexenal, (E)-2-hexenal, (Z)-3-hexenol, (E)-2-hexenol, and (Z)-3-hexen-1-yl acetate. Blend 2 (B2) contained six plant volatiles, namely (Z)-ocimene, linalool, benzyl acetate, methyl salicylate, β-caryophyllene, and (E)-β-farnesene. Each blend was made available in four different amounts of volatiles, corresponding to each compound being added to 50 µL of hexane in amounts of 1, 5, 25 and 125 ng. The effects of the two blends at the different concentrations on the insects were evaluated using a Y-tube olfactometer. Both sexes of the insects were found to be significantly repelled by the highest volatile levels of B1 and by two levels of B2 (25 and 125 ng). Females were also observed to be repelled using B2 with 5 ng of each volatile. Attraction was observed for both sexes only for B1 at the three lower volatile levels (1, 5 and 25 ng). In additional experiments, using only attractants, unmated females were found to be attracted to males, whereas mated females were only attracted to B1. Both unmated and mated males (previously observed in copula) were attracted only to females.

A closer look at sex pheromone autodetection in the Oriental fruit moth

Female moths emit sex pheromone to attracts males, and although they are not attracted to their own sex pheromone, they appear to detect it as it affects their behavior. In order to elucidate the mechanism of pheromone “autodetection” we compared responses of olfactory receptor neurons (ORNs) of male and female Grapholita molesta, a species with reported pheromone autodetection. Two concentrations of the major (Z8-12:Ac) and minor (E8-12:Ac) sex pheromone components, a plant-volatile blend containing methyl salicylate, terpinyl acetate and (E)-β-farnesene, and the male-produced hair-pencil (i.e., courtship) pheromone (ethyl trans-cinnamate) were tested in 45 male and 305 female ORNs. Hierarchical cluster analysis showed radically different peripheral olfactory systems between sexes that could be linked to their specific roles. In males 63% of the ORNs were tuned specifically to the major or minor female sex pheromone components, and 4% to the plant volatile blend, while the remaining 33% showed unspecific responses to the stimulus panel. In females 3% of the ORNs were specifically tuned to the male hair-pencil pheromone, 6% to the plant volatile blend, 91% were unspecific, and no ORN was tuned their own sex pheromone components. The lack of sex pheromone-specific ORNs in females suggests that they are not able to discriminate pheromone blends, and thus pheromone autodetection is unlikely in this species. We discuss our results in the context of the methodological limitations inherent to odor stimulation studies.

Variation in the ratio of compounds in a plant volatile blend during transmission by wind

For plant volatiles to mediate interactions in tritrophic systems, they must convey accurate and reliable information to insects. However, it is unknown whether the ratio of compounds in plant volatile blends remains stable during wind transmission. In this study, volatiles released from an odor source were collected at different points in a wind tunnel and analyzed. The variation in the amounts of volatiles collected at different points formed a rough cone shape. The amounts of volatiles collected tended to decrease with increasing distance from the odor source. Principal component analyses showed that the volatile profiles were dissimilar among different collection points. The profiles of volatiles collected nearest the odor source were the most similar to the released odor. Higher wind speed resulted in a clearer spatial distribution of volatile compounds. Thus, variations in the ratios of compounds in odor plumes exist even during transport over short distances.

Eliciting Plant Defenses Through Herbivore-Induced Plant Volatiles’ Exposure in Sweet Peppers

Insect herbivory activates plant defense mechanisms and releases a blend of herbivore-induced plant volatiles (HIPVs). These volatile compounds may be involved in plant-plant communication and induce defense response in undamaged plants. In this work, we investigated whether the exposure of sweet pepper plants to HIPVs [(Z)-3-hexenol, (Z)-3-hexenyl acetate, (Z)-3-hexenyl propanoate, (Z)-3-hexenyl butanoate, hexyl butanoate, methyl salicylate and methyl jasmonate] activates the sweet pepper immune defense system. For this, healthy sweet pepper plants were individually exposed to the each of the above mentioned HIPVs over 48 h. The expression of jasmonic acid and salicylic acid related genes was quantified. Here, we show that all the tested volatiles induced plant defenses by upregulating the jasmonic acid and salicylic acid signaling pathway. Additionally, the response of Frankliniella occidentalis, a key sweet pepper pest, and Orius laevigatus, the main natural enemy of F. occidentalis, to HIPV-exposed sweet pepper plants were studied in a Y-tube olfactometer. Only plants exposed to (Z)-3-hexenyl propanoate and methyl salicylate repelled F. occidentalis whereas O. laevigatus showed a strong preference to plants exposed to (Z)-3-hexenol, (Z)-3-hexenyl propanoate, (Z)-3-hexenyl butanoate, methyl salicylate and methyl jasmonate. Our results show that HIPVs act as elicitors to sweet pepper plant defenses by enhancing defensive signaling pathways. We anticipate our results to be a starting point for integrating HIPVs-based approaches in sweet pepper pest management systems which may provide a sustainable strategy to manage insect pests in horticultural plants.

Terpene synthases in cucumber (Cucumis sativus) and their contribution to herbivore-induced volatile terpenoid emission.

Summary Terpenoids play important roles in flavour, pollinator attraction and defence of plants. In cucumber (Cucumis sativus) they are important components of the herbivore‐induced plant volatile blend that attracts natural enemies of herbivores.We annotated the cucumber TERPENE SYNTHASE gene (CsTPS) family and characterized their involvement in the response towards herbivores with different feeding guilds using a combined molecular and biochemical approach.Transcripts of multiple CsTPS genes were upregulated in leaves upon herbivory and the products generated by the expressed proteins match the terpenoids recorded in the volatile blend released by herbivore‐damaged leaves. Spatial and temporal analysis of the promoter activity of CsTPS genes showed that cell content‐feeding spider mites (Tetranychus urticae) and thrips (Frankliniella occidentalis) induced promoter activity of CsTPS9 and CsTPS19 within hours after initiation of infestation, while phloem‐feeding aphids (Myzus persicae) induced CsTPS2 promoter activity.Our findings offer detailed insights into the involvement of the TPS gene family in the dynamics and fine‐tuning of the emission of herbivore‐induced plant volatiles in cucumber, and open a new avenue to understand molecular mechanisms that affect plant–herbivore interactions.

Silicon suppresses a ubiquitous mite herbivore and promotes natural enemy attraction by altering plant volatile blends

Silicon (Si) accumulation in plants is widely recognised as an effective physical defence against chewing herbivores. However, its effects on some feeding guilds such as cell-content feeders are understudied despite being severe economic pests (e.g. Tetranychus urticae). Moreover, most studies focus on direct impacts of Si, but there is growing evidence that Si also impacts indirect defence. We examined the effects of Si on French bean, Phaseolus vulgaris, defences against the two-spotted spider mite, T. urticae. We grew plants hydroponically with (+ Si) or without (–Si) silicon, assessed T. urticae performance and tested the preference of the predatory mite, Phytoseiulus persimilis, for volatiles from T. urticae-infested (+ M) or uninfested (–M) plants. The provision of Si to plants suppressed T. urticae egg-laying, population growth and leaflet damage, and partially ameliorated T. urticae-induced reductions in stomatal conductance and net photosynthesis. Furthermore, T. urticae infestation increased foliar Si accumulation. Predatory mites were more attracted (64%) to volatiles from + Si plants experiencing herbivory than to –Si plants. The relative emissions (%) of volatile compounds, viz. E-2-hexanyl benzoate, hexanal, E-trans-β-ocimene, D-limonene, β-caryophyllene and methyl salicylate were elevated from + Si + M plants, while the relative emissions of 3-hexanol, trans-calamenene, o-xylene and o-cymene were lowered compared to –Si + M plants. Our results show, for the first time, that Si defences are inducible and effective even in low Si-accumulating plants against T. urticae and suggest that Si could play a role in pest biocontrol.

Olfactory responses of Argentine stem weevil to herbivory and endophyte-colonisation in perennial ryegrass

Argentine stem weevil adults (ASW, Listronotus bonariensis) feed on the leaves of agricultural grasses and their larvae mine the pseudostem, causing extensive damage that can result in plant death. Plants emit volatiles that serve as signals to host-searching insects and these odours can be altered by both herbivory and fungal endophyte-infection. This study investigated whether ASW adults utilise olfaction to identify their host plants, perennial ryegrass (Lolium perenne), and if conspecific herbivory or the presence of Epichloë festucae var. lolii fungal endophytes (strain wild-type or AR1) influenced such responses. Results from olfactometer bioassays established that ASW adults were able to utilise their olfactory response to orient towards volatiles released by perennial ryegrass and further, the weevils displayed a preference for plants previously damaged by conspecific weevils. However, there was no evidence that weevils had the ability to distinguish between endophyte-infected and endophyte-free plants using olfaction alone. Using a push–pull extraction technique, thirteen volatile compounds were identified in the blend released by perennial ryegrass. Endophyte and herbivory were found to alter these volatile compounds and quantities emitted by this forage grass. This study suggests that despite observing differences in the plant volatile blend, ASW do not perceive endophyte (wild-type and AR1) using olfaction alone and must rely on other cues, e.g. contact chemoreception or post-ingestional malaise, to detect the presence of a bioactive endophyte in an otherwise acceptable host plant.

Plant volatiles as regulators of plant defense and herbivore immunity: molecular mechanisms and unanswered questions.

Plants release distinct blends of herbivore-induced plant volatiles (HIPVs) upon herbivore attack. HIPVs have long been known to influence the behavior of herbivores and natural enemies. In addition, HIPVs can act as physiological regulators that induce or prime plant defenses. Recent work indicates that the regulatory capacity of HIPVs may extend to herbivore immunity: herbivores that are exposed to HIPVs can become more resistant or susceptible to parasitoids and pathogens. While the mechanisms of HIPV-mediated plant defense regulation are being unraveled, the mechanisms underlying the regulation of herbivore immunity are unclear. Evidence so far suggests a high degree of context dependency. Here, we review the mechanisms by which HIPVs regulate plant defense and herbivore immunity. We address major gaps of knowledge and discuss directions for future mechanistic research to facilitate efforts to use the regulatory capacity of HIPVs for the biological control of insect pests.

Habitat cues synergize to elicit chemically mediated landing behavior in a specialist phytophagous insect, the grape berry moth

AbstractMany phytophagous insects locate their host plant using mixtures of volatile compounds produced by the plant. A key behavior in the host location process that has been the focus of decades of behavioral research is optomotor anemotaxis. Another key step in host location is landing on (or near) the odor source. In previous work, rubber septa emitting a synthetic blend of volatiles extracted from young shoots of grape plants, Vitus spp. (Vitaceae), elicited equivalent levels of oriented upwind flight by female grape berry moths (GBM), Paralobesia viteana (Clemens) (Lepidoptera: Tortricidae), as did actual (control) grape shoots. However, in contrast to the shoots, females did not land on the odor source. In this study, we used flight tunnel assays to investigate the landing response of GBM females with respect to chemical and visual stimuli, as well as differences in relative humidity. When stimuli were presented individually, only the synthetic blend of host plant volatiles elicited equivalent levels of oriented upwind flight compared to the plants. Interestingly, wet cotton strips elicited low but consistent levels of upwind flight. In paired assays, only the synthetic blend paired with wet cotton strips elicited landing, although at significantly lower levels than that elicited by grape shoots. To achieve landing rates equivalent to live grape shoots, grape berry moth females required all three stimuli we tested: host odor cues, moisture, and visual cues simulating a grape shoot. These results suggest the cues have a synergistic effect, and that landing behavior requires complex sensory processing using multiple sensory inputs. Furthermore, these results suggest that moisture plays an important role in the host plant location process.

Targeting diamondback moths in greenhouses by attracting specific native parasitoids with herbivory-induced plant volatiles.

We investigated the recruitment of specific parasitoids using a specific blend of synthetic herbivory-induced plant volatiles (HIPVs) as a novel method of pest control in greenhouses. In the Miyama rural area in Kyoto, Japan, diamondback moth (DBM) (Plutella xylostella, Lepidoptera: Plutellidae) larvae are an important pest of cruciferous crops in greenhouses, and Cotesia vestalis (Hymenoptera: Braconidae), a larval parasitoid of DBM, is found in the surrounding areas. Dispensers of HIPVs that attracted C. vestalis and honey feeders were set inside greenhouses (treated greenhouses). The monthly incidence of DBMs in the treated greenhouses was significantly lower than that in the untreated greenhouses over a 2-year period. The monthly incidences of C. vestalis and DBMs were not significantly different in the untreated greenhouses, whereas monthly C. vestalis incidence was significantly higher than monthly DBM incidence in the treated greenhouses. Poisson regression analyses showed that, in both years, a significantly higher number of C. vestalis was recorded in the treated greenhouses than in the untreated greenhouses when the number of DBM adults increased. We concluded that DBMs were suppressed more effectively by C. vestalis in the treated greenhouses than in the untreated greenhouses.

Fruit Volatiles of Creeping Cucumber (Solena amplexicaulis) Attract a Generalist Insect Herbivore.

Herbivorous insects employ host plant volatile blends as cue for host recognition. Adults of Aulacophora foveicollis Lucas (Coleoptera: Chrysomelidae) feed on leaves, flowers, and fruits of Solena amplexicaulis (Lam.) Gandhi (syn: Melothria heterophylla) (Cucurbitaceae), commonly known as creeping cucumber. Currently, this pest is controlled by insecticides application. Hence, it is necessary to find out volatile components from fruits attracting the insect, which might be used for eco-friendly pest management program. behavioral responses of females were measured by Y-tube olfactometer bioassays towards volatile blends from undamaged (UD), insect-damaged (ID), and mechanically damaged (MD) fruits with the aim to identify the compounds responsible for host fruit location. Volatile organic compounds were identified and quantified by GC-MS and GC-FID analyses, respectively. Nonanal was predominant in volatile blends of UD, ID, and MD fruits. 1-Octen-3-ol, 3-octanone, 2-octanol, heptadienal (2E,4E), 1-pentadecanol, and 1-hexadecanol were present in volatile blends of ID and MD fruits, but females did not show response to these six compounds. 1-Octanol and 1-heptadecanol were unique in volatile blends of UD fruits after 4hr of damage, but females did not show response to these compounds. Females were more attracted to volatile blends from UD fruits after 4hr of damage in comparison to volatile blends released by UD fruits, due to increased emissions of (E,Z)-2,6-nonadienal and 2E-nonenal. A synthetic blend of 3.35μg (E,Z)-2,6-nonadienal and 1.72μg 2E-nonenal dissolved in 25μl CH2Cl2 could be used for the development of baited traps to control this insect pest in integrated pest management strategies.

A male-produced aggregation-sex pheromone of the beetle Arhopalus rusticus (Coleoptera: Cerambycidae, Spondylinae) may be useful in managing this invasive species

The longhorned beetle Arhopalus rusticus (Coleoptera: Cerambycidae, Spondylinae) is a common species in conifer forests of the Northern Hemisphere, but with global trade, it has invaded and become established in New Zealand, Australia, and South America. Arhopalus rusticus is a suspected vector of the phytopathogenic nematode, Bursaphelenchus xylophilus, the causative agent of pine wilt disease, which is a major threat to pine forests worldwide. Here, we report the identification of a volatile, male-produced aggregation-sex pheromone for this species. Headspace odours from males contained a major male-specific compound, identified as (2 S, 5E)-6,10-dimethyl-5,9-undecadien-2-ol (common name (S)-fuscumol), and a minor component (E)-6,10-dimethyl-5,9-undecadien-2-one (geranylacetone). Both compounds are known pheromone components for species in the same subfamily. In field trials in its native range in Slovenia, (S)-fuscumol was significantly more attractive to beetles of both sexes, than racemic fuscumol and a blend of host plant volatiles commonly used as an attractant for this species. Fuscumol-baited traps also caught significant numbers of another spondylidine species, Spondylis buprestoides (L.), and a rare click beetle, Stenagostus rufus (De Geer). The pheromone can be exploited as a cost-effective and environmentally safe tool for detection and monitoring of this invasive species at ports of entry, and for monitoring the beetle’s distribution and population trends in both endemic and invasive populations.

What makes a volatile organic compound a reliable indicator of insect herbivory?

Plants that are subject to insect herbivory emit a blend of so‐called herbivore‐induced plant volatiles (HIPVs), of which only a few serve as cues for the carnivorous enemies to locate their host. We lack understanding which HIPVs are reliable indicators of insect herbivory. Here, we take a modelling approach to elucidate which physicochemical and physiological properties contribute to the information value of a HIPV. A leaf‐level HIPV synthesis and emission model is developed and parameterized to poplar. Next, HIPV concentrations within the canopy are inferred as a function of dispersion, transport and chemical degradation of the compounds. We show that the ability of HIPVs to reveal herbivory varies from almost perfect to no better than chance and interacts with canopy conditions. Model predictions matched well with leaf‐emission measurements and field and laboratory assays. The chemical class a compound belongs to predicted the signalling ability of a compound only to a minor extent, whereas compound characteristics such as its reaction rate with atmospheric oxidants, biosynthesis rate upon herbivory and volatility were much more important predictors. This study shows the power of merging fields of plant–insect interactions and atmospheric chemistry research to increase our understanding of the ecological significance of HIPVs.