Solvent Extraction of PDMS Tubing as a New Method for the Capture of Volatile Organic Compounds from Headspace.

Polydimethylsiloxane (PDMS) tubing is increasingly being used to collect volatile organic compounds (VOCs) from static biological headspace. However, analysis of VOCs collected using PDMS tubing often deploys thermal desorption, where samples are considered as 'one-offs' and cannot be used in multiple experiments. In this study, we developed a static headspace VOC collection method using PDMS tubing which is solvent-based, meaning that VOC extracts can be used multiple times and can be linked to biological activity. Using a synthetic blend containing a range of known semiochemicals (allyl isothiocyanate, (Z)-3-hexen-1-ol, 1-octen-3-one, nonanal, (E)-anethol, (S)-bornyl acetate, (E)-caryophyllene and pentadecane) with differing chemical and physicochemical properties, VOCs were collected in static headspace by exposure to PDMS tubing with differing doses, sampling times and lengths. In a second experiment, VOCs from oranges were collected using PDMS sampling of static headspace versus dynamic headspace collection. VOCs were eluted with diethyl ether and analysed using gas chromatography - flame ionization detector (GC-FID) and coupled GC - mass spectrometry. GC-FID analysis of collected samples showed that longer PDMS tubes captured significantly greater quantities of compounds than shorter tubes, and that sampling duration significantly altered the recovery of all tested compounds. Moreover, greater quantities of compounds were recovered from closed compared to open systems. Finally, analysis of orange headspace VOCs showed no qualitative differences in VOCs recovered compared to dynamic headspace collections, although quantities sampled using PDMS tubing were lower. In summary, extraction of PDMS tubing with diethyl ether solvent captures VOCs from the headspace of synthetic blends and biological samples, and the resulting extracts can be used for multiple experiments linking VOC content to biological activity.

L-DOPA functions as a plant pheromone for belowground anti-herbivory communication.

While mechanisms of plant-plant communication for alerting neighbouring plants of an imminent insect herbivore attack have been described aboveground via the production of volatile organic compounds (VOCs), we are yet to decipher the specific components of plant-plant signalling belowground. Using bioassay-guided fractionation, we isolated and identified the non-protein amino acid l-DOPA, released from roots of Acyrtosiphon pisum aphid-infested Vicia faba plants, as an active compound in triggering the production of VOCs released aboveground in uninfested plants. In behavioural assays, we show that after contact with l-DOPA, healthy plants become highly attractive to the aphid parasitoid (Aphidius ervi), as if they were infested by aphids. We conclude that l-DOPA, originally described as a brain neurotransmitter precursor, can also enhance immunity in plants.

(-)-Adaline from the Adalia Genus of Ladybirds Is a Potent Antagonist of Insect and Specific Mammalian Nicotinic Acetylcholine Receptors.

Ladybird beetles (Coleoptera: Coccinellidae) possess strong chemical defences that are secreted in response to stress and are also found on the coating of eggs, which are rich in alkaloids that are responsible for their toxicity to other species. Recent studies have shown that alkaloids from several species of ladybird beetle can target nicotinic acetylcholine receptors (nAChRs) acting as receptor antagonists. Here, we have explored the actions of (-)-adaline, found in the 2-spot (Adalia bipunctata) and 10-spot (Adalia decempunctata) ladybirds, on both mammalian (α1ß1γδ, α7, α4ß2, α3ß4) and insect nAChRs using patch-clamp of TE671 cells and locust brain neurons natively expressing nAChRs, as well as two-electrode voltage clamp of Xenopus laevis oocytes recombinantly expressing nAChRs. All nAChR subtypes were antagonised by (-)-adaline in a time-dependent, voltage-dependent and non-competitive manner with the lowest IC50s at rat α3ß4 (0.10 µM) and locust neuron (1.28 µM) nAChRs, at a holding potential of -75 mV. The data imply that (-)-adaline acts as an open channel blocker of nAChRs.

Iridoid Sex Pheromone Biosynthesis in Aphids Mimics Iridoid-Producing Plants.

Biosynthesis of (1R,4aS,7S,7aR)-nepetalactol (1) and (4aS,7S,7aR)-nepetalactone (2) in plants involves iridoid synthase (ISY), an atypical reductive cyclase that catalyses the reduction of 8-oxogeranial into the reactive enol of (S)-8-oxocitronellal, and cyclization of this enol intermediate, either non-enzymatically or by a nepetalactol-related short chain dehydrogenase enzyme (NEPS) that yields the nepetalactols. In this study, we investigated the biosynthesis in vivo of 1 and 2 in the pea aphid, Acyrthosiphon pisum, using a library of isotopically-labelled monoterpenoids as molecular probes. Topical application of deuterium-labelled probes synthesized from geraniol and nerol resulted in production of 2 H4 -lactol 1 and 2 H4 -lactone 2. However, deuterium incorporation was not evident using labelled probes synthesized from (S)-citronellol. These results suggest that iridoid biosynthesis in animals, specifically aphids, may follow a broadly similar route to that characterised for plants.

Bumblebee electric charge stimulates floral volatile emissions in Petunia integrifolia but not in Antirrhinum majus.

The timing of volatile organic compound (VOC) emission by flowering plants often coincides with pollinator foraging activity. Volatile emission is often considered to be paced by environmental variables, such as light intensity, and/or by circadian rhythmicity. The question arises as to what extent pollinators themselves provide information about their presence, in keeping with their long co-evolution with flowering plants. Bumblebees are electrically charged and provide electrical stimulation when visiting plants, as measured via the depolarisation of electric potential in the stem of flowers. Here we test the hypothesis that the electric charge of foraging bumblebees increases the floral volatile emissions of bee pollinated plants. We investigate the change in VOC emissions of two bee-pollinated plants (Petunia integrifolia and Antirrhinum majus) exposed to the electric charge typical of foraging bumblebees. P. integrifolia slightly increases its emissions of a behaviorally and physiologically active compound in response to visits by foraging bumblebees, presenting on average 121 pC of electric charge. We show that for P. integrifolia, strong electrical stimulation (600-700 pC) promotes increased volatile emissions, but this is not found when using weaker electrical charges more representative of flying pollinators (100 pC). Floral volatile emissions of A. majus were not affected by either strong (600-700 pC) or weak electric charges (100 pC). This study opens a new area of research whereby the electrical charge of flying insects may provide information to plants on the presence and phenology of their pollinators. As a form of electroreception, this sensory process would bear adaptive value, enabling plants to better ensure that their attractive chemical messages are released when a potential recipient is present.

Development of a Phytochemical-Based Lure for the Dried Bean Beetle Acanthoscelides obtectus Say (Coleoptera: Chrysomelidae).

The dried bean beetle, Acanthoscelides obtectus, is an economically important, worldwide pest of legume crops including dry beans, Phaseolus vulgaris. Assessment of A. obtectus infestation levels in pre-harvest field crops and post-harvest granaries is difficult to achieve because there is no effective monitoring tool for early detection so that interventions can be deployed as needed. Because A. obtectus is a generic pollen and nectar feeder, we adopted an electrophysiological (EAG) screening approach, using the antennae of female A. obtectus to identify physiologically active, volatile phytochemicals, which could then be investigated for their attractiveness to A. obtectus in laboratory behavioral assays and preliminary field tests. Of the 27 compounds tested in EAG screening, 5 compounds, i.e., methyl anthranilate, methyl eugenol, benzyl alcohol, (RS)-lavandulol, and 2-phenylethanol, elicited stronger EAG responses than the standard (1-phenylethanol). In 4-arm olfactometer bioassays, female A. obtectus preferred the olfactometer arm containing the odor of either methyl anthranilate or benzyl alcohol compared to the solvent control. In preliminary field tests using these 2 compounds as a binary mixture, at least 5 times as many beetles were caught on baited traps compared to non-baited traps. The field data also suggested that benzyl alcohol was primarily responsible for the field activity of the blend. We hypothesize that the attraction of A. obtectus to the combined benzyl alcohol/methyl anthranilate and the single benzyl alcohol baits is connected to the species` nectar- and pollen-feeding behaviour and not to its intraspecific communication. To our knowledge, this is the first evidence that A. obtectus behavior in the field can be modified by the deployment of plant-derived semiochemicals.

Sex Pheromone of the Alfalfa Plant Bug, Adelphocoris lineolatus: Pheromone Composition and Antagonistic Effect of 1-Hexanol (Hemiptera: Miridae).

The sex pheromone composition of alfalfa plant bugs, Adelphocoris lineolatus (Goeze), from Central Europe was investigated to test the hypothesis that insect species across a wide geographical area can vary in pheromone composition. Potential interactions between the pheromone and a known attractant, (E)-cinnamaldehyde, were also assessed. Coupled gas chromatography-electroantennography (GC-EAG) using male antennae and volatile extracts collected from females, previously shown to attract males in field experiments, revealed the presence of three physiologically active compounds. These were identified by coupled GC/mass spectrometry (GC/MS) and peak enhancement as hexyl butyrate, (E)-2-hexenyl butyrate and (E)-4-oxo-2-hexenal. A ternary blend of these compounds in a 5.4:9.0:1.0 ratio attracted male A. lineolatus in field trials in Hungary. Omission of either (E)-2-hexenyl-butyrate or (E)-4-oxo-2-hexenal from the ternary blend or substitution of (E)-4-oxo-2-hexenal by (E)-2-hexenal resulted in loss of activity. These results indicate that this Central European population is similar in pheromone composition to that previously reported for an East Asian population. Interestingly, another EAG-active compound, 1-hexanol, was also present in female extract. When 1-hexanol was tested in combination with the ternary pheromone blend, male catches were reduced. This compound showed a dose-response effect with small doses showing a strong behavioral effect, suggesting that 1-hexanol may act as a sex pheromone antagonist in A. lineolatus. Furthermore, when (E)-cinnamaldehyde was field tested in combination with the sex pheromone, there was no increase in male catch, but the combination attracted both males and females. Prospects for practical application are discussed.

Plasmodium-associated changes in human odor attract mosquitoes.

Malaria parasites (Plasmodium) can change the attractiveness of their vertebrate hosts to Anopheles vectors, leading to a greater number of vector-host contacts and increased transmission. Indeed, naturally Plasmodium-infected children have been shown to attract more mosquitoes than parasite-free children. Here, we demonstrate Plasmodium-induced increases in the attractiveness of skin odor in Kenyan children and reveal quantitative differences in the production of specific odor components in infected vs. parasite-free individuals. We found the aldehydes heptanal, octanal, and nonanal to be produced in greater amounts by infected individuals and detected by mosquito antennae. In behavioral experiments, we demonstrated that these, and other, Plasmodium-induced aldehydes enhanced the attractiveness of a synthetic odor blend mimicking "healthy" human odor. Heptanal alone increased the attractiveness of "parasite-free" natural human odor. Should the increased production of these aldehydes by Plasmodium-infected humans lead to increased mosquito biting in a natural setting, this would likely affect the transmission of malaria.

Effects of Nicotine and Tobacco-Related Products on the Feeding Behavior of the German Cockroach (Blattodea: Blattellidae).

Animals use olfaction to detect developmentally significant volatile organic compounds (VOCs) in their local environment. As part of a wider study aiming to demonstrate that the olfactory responses of animals to VOCs can be modified through the creation of a drug-addicted status and association with a selected VOC, we investigated nicotine and tobacco smoke particulate (TSP) extract as possible addictive compounds for male German cockroaches, Blattella germanica (Linnaeus). In feeding experiments using an artificial food stimulus, food treated with TSP extract was preferred over untreated food. Surprisingly, nicotine, which was expected to be the most important addictive tobacco component, did not induce noticeable effects on cockroach behavior. Both TSP extract and nicotine were shown to be phagostimulants. Olfactometry assays that measured odor-mediated insect behavior demonstrated that male B. germanica did not choose TSP-extract-treated food even when attempts were made specifically to train them via this modality. These results support a hypothesis that B. germanica needs to consume TSP-containing food to show a clear preference for this stimulus and that gustatory mechanisms are involved due to compounds present in the TSP extract.

Recent progress in the synthesis of homotropane alkaloids adaline, euphococcinine and N-methyleuphococcinine.

The 9-azabicyclo[3.3.1]nonane ring system is present in several insect- and plant-derived alkaloids. (-)-Adaline (1) and (+)-euphococcinine (2), found in secretions of Coccinelid beetles, and (+)-N-methyleuphococcinine (3), isolated from the Colorado blue spruce Picea pungens, are members of this alkaloid family. Their unique bicyclic system with a quaternary stereocenter, and the potent biological activity exerted by these homotropane alkaloids, make them attractive synthetic targets. This work aims briefly to review the chemical ecology of Adalia bipunctata and the recent methodologies to obtain adaline (1), euphococcinine (2), and N-methyleuphococcinine (3).

Inefficient weapon-the role of plant secondary metabolites in cotton defence against the boll weevil.

MAIN CONCLUSION: Cotton genotypes displayed similar volatile organic compound (VOC) profiles, but major differences in terpenoid aldehyde (TA) content. The differences in VOC production were minor among genotypes, but these differences are crucial for boll weevil attraction. Weevils did not display any preference in feeding behaviour towards cotton genotypes, suggesting physiological adaptation to cope with cotton chemical defence mechanisms. Plant cultivar selection for resistance to herbivore pests is an effective, environmentally safe and inexpensive method to implement in integrated pest management programmes. In this study, we evaluated seven cotton genotypes with respect to the production of volatile organic compounds (VOCs) and non-volatile compounds [terpenoid aldehydes (TAs)], and the attraction and feeding preference of adult boll weevils. Chemical analyses of VOCs from BRS-293, BRS-Rubi, CNPA TB-15, CNPA TB-85, CNPA TB-90, Delta Opal, and Empire Glandless showed that there were few qualitative and quantitative differences across the range of genotypes. In contrast, major differences in TA content were observed, with CNPA TB-15 and CNPA TB-85 producing higher levels of TAs compared to the other genotypes. Our results showed that boll weevil attraction to cotton genotypes varied, suggesting that the ratios and quantities of emitted cotton VOCs are important for host location. However, boll weevil feeding behaviour was neither positively nor negatively influenced by the terpenoid content (non-volatile compounds) of cotton genotypes. The results in this study suggest that boll weevils have adapted physiologically to cope with cotton chemical defence mechanisms.

Identification of Semiochemicals from Cowpea, Vigna unguiculata, for Low-input Management of the Legume Pod Borer, Maruca vitrata.

Cowpea, Vigna unguiculata L. Walp. (Fabaceae), is one of the most important food legumes grown on the African continent, as it provides an affordable source of dietary protein. Yields of cowpea are significantly reduced through damage by legume pod-borer, Maruca vitrata (Lepidoptera: Crambidae), caterpillars to flowers, tender leaves and pods. Semiochemical-based strategies are considered as environmentally benign and affordable for pest management, particularly on smallholder farms. In this study, we investigated the importance of cowpea flower volatiles as host location cues for egg-laying M. vitrata, and herbivore-induced plant volatiles (HIPVs) as M. vitrata repellents and natural enemy (Apanteles taragamae and Phanerotoma syleptae parasitoid) attractants. In oviposition choice assays, M. vitrata laid more eggs on flowering cowpea plants than non-flowering plants. Coupled gas chromatography-electrophysiology (GC-EAG) analysis using the antennae of female M. vitrata and an extract of flower volatiles collected by dynamic headspace collection revealed the presence of five EAG-active components that were identified by coupled GC-mass spectrometry (GC-MS) analysis as benzaldehyde, benzyl alcohol, acetophenone, a vinylbenzaldehyde isomer and (E)-cinnamaldehyde. A synthetic blend of the identified compounds, prepared using 3-vinylbenzaldehyde, induced M. vitrata to lay as many eggs on non-flowering cowpea as on flowering plants. The moths also preferred laying eggs on intact plants compared to M. vitrata-infested plants. As the emission of EAG-active floral compounds was determined to be lower in the headspace of infested cowpea flowers, the role of HIPVs emitted by M. vitrata-damaged leaves was also investigated. Of the compounds induced by larval damage, (E)-DMNT, indole, n-hexyl acetate, 1-octen-3-ol and linalool were shown by GC-EAG to possess electrophysiological activity. A synthetic blend of the EAG-active compounds, using racemic 1-octen-3-ol and linalool, significantly reduced egg numbers on flowering cowpea. Larval and egg parasitoids, i.e. A. taragamae and Ph. syleptae, respectively, of M. vitrata both preferred the Y-tube olfactometer arm treated with synthetic (E)-DMNT, whereas preference for racemic linalool and (E)-nerolidol was dose-dependent in A. taragamae. Our results provide the platform for the development of future semiochemical-based pest management strategies against M. vitrata on smallholder farms in West Africa.

Actions on mammalian and insect nicotinic acetylcholine receptors of harmonine-containing alkaloid extracts from the harlequin ladybird Harmonia axyridis.

The harlequin ladybird, Harmonia axyridis (H. axyridis), possesses a strong chemical defence that has contributed to its invasive success. Ladybird beetle defensive chemicals, secreted in response to stress and also found on the coating of laid eggs, are rich in alkaloids that are thought to be responsible for this beetle's toxicity to other species. Recent studies have shown that alkaloids from several species of ladybird beetle can target nicotinic acetylcholine receptors (nAChRs) acting as receptor antagonists, hence we have explored the actions of alkaloids of the ladybird H. axyridis on both mammalian and insect nAChRs. Electrophysiological studies on native and functionally expressed recombinant nAChRs were used to establish whether an alkaloid extract from H. axyridis (HAE) targeted nAChRs and whether any selectivity exists for insect over mammalian receptors of this type. HAE was found to be an inhibitor of all nAChRs tested with the voltage-dependence of inhibition and the effect on ACh EC50 differing between nAChR subtypes. Our finding that an HAE fraction consisting almost entirely of harmonine had a strong inhibitory effect points to this alkaloid as a key component of nAChR inhibitory actions. Comparison of HAE inhibition between the mammalian and insect nAChRs investigated indicates some preference for the insect nAChR supporting the view that investigation of ladybird alkaloids shows promise as a method for identifying natural product leads for future insecticide development.

Molasses Grass Induces Direct and Indirect Defense Responses in Neighbouring Maize Plants.

Plants have evolved intricate defence strategies against herbivore attack which can include activation of defence in response to stress-related volatile organic compounds (VOCs) emitted by neighbouring plants. VOCs released by intact molasses grass (Melinis minutiflora), have been shown to repel stemborer, Chilo partellus (Swinhoe), from maize and enhance parasitism by Cotesia sesamiae (Cameron). In this study, we tested whether the molasses grass VOCs have a role in plant-plant communication by exposing different maize cultivars to molasses grass for a 3-week induction period and then observing insect responses to the exposed plants. In bioassays, C. partellus preferred non-exposed maize landrace plants for egg deposition to those exposed to molasses grass. Conversely, C. sesamiae parasitoid wasps preferred volatiles from molasses grass exposed maize landraces compared to volatiles from unexposed control plants. Interestingly, the molasses grass induced defence responses were not observed on hybrid maize varieties tested, suggesting that the effect was not simply due to absorption and re-emission of VOCs. Chemical and electrophysiological analyses revealed strong induction of bioactive compounds such as (R)-linalool, (E)-4,8-dimethyl-1,3,7-nonatriene and (E,E)-4,8,12-trimethyl-1,3,7,11-tridecatetraene from maize landraces exposed to molasses grass volatiles. Our results suggest that constitutively emitted molasses grass VOCs can induce direct and indirect defence responses in neighbouring maize landraces. Plants activating defences by VOC exposure alone could realize enhanced levels of resistance and fitness compared to those that launch defence responses upon herbivore attack. Opportunities for exploiting plant-plant signalling to develop ecologically sustainable crop protection strategies against devastating insect pests such as stemborer C. partellus are discussed.

Expression of lima bean terpene synthases in rice enhances recruitment of a beneficial enemy of a major rice pest.

Volatile terpenoids play a key role in plant defence against herbivory by attracting parasitic wasps. We identified seven terpene synthase genes from lima bean, Phaseolus lunatus L. following treatment with either the elicitor alamethicin or spider mites, Tetranychus cinnabarinus. Four of the genes (Pltps2, Pltps3, Pltps4 and Pltps5) were up-regulated with their derived proteins phylogenetically clustered in the TPS-g subfamily and PlTPS3 positioned at the base of this cluster. Recombinant PlTPS3 was able to convert geranyl diphosphate and farnesyl diphosphate to linalool and (E)-nerolidol, the latter being precursor of the homoterpene (E)-4,8-dimethyl-1,3,7-nonatriene (DMNT). Recombinant PlTPS4 showed a different substrate specificity and produced linalool and (E)-nerolidol, as well as (E,E)-geranyllinalool from geranylgeranyl diphosphate. Transgenic rice expressing Pltps3 emitted significantly more (S)-linalool and DMNT than wild-type plants, whereas transgenic rice expressing Pltps4 produced (S)-linalool, DMNT and (E,E)-4,8,12-trimethyl-1,3,7,11-tridecatetraene (TMTT). In laboratory bioassays, female Cotesia chilonis, the natural enemy of the striped rice stemborer, Chilo suppressalis, were significantly attracted to the transgenic plants and their volatiles. We further confirmed this with synthetic blends mimicking natural rice volatile composition. Our study demonstrates that the transformation of rice to produce volatile terpenoids has the potential to enhance plant indirect defence through natural enemy recruitment.

(2R,5S)-Theaspirane Identified as the Kairomone for the Banana Weevil, Cosmopolites sordidus, from Attractive Senesced Leaves of the Host Banana, Musa spp.

The principal active component produced by highly attractive senesced host banana leaves, Musa spp., for the banana weevil, Cosmopolites sordidus, is shown by coupled gas chromatography-electroantennography (GC-EAG), coupled GC-mass spectrometry (GC-MS), chemical synthesis and coupled enantioselective (chiral) GC-EAG to be (2R,5S)-theaspirane. In laboratory behaviour tests, the synthetic compound is as attractive as natural host leaf material and presents a new opportunity for pest control.

Attractiveness of Host Plant Volatile Extracts to the Asian Citrus Psyllid, Diaphorina citri, is Reduced by Terpenoids from the Non-Host Cashew.

Diaphorina citri is a vector of the bacterial causative agent of Huanglongbing (HLB = Citrus greening), a severe disease affecting citrus crops. As there is no known control for HLB, manipulating insect behaviour through deployment of semiochemicals offers a promising opportunity for protecting citrus crops. The behavioural responses of D. citri to plant volatiles, and the identity of these plant volatiles were investigated. Volatiles were collected from host plants Murraya paniculata, Citrus sinensis, C. reshni, C. limettioides, Poncirus trifoliata, and from non-host plants Psidium guajava, Mangifera indica, Anacardium occidentale. In behavioural assays, female D. citri spent more time in the arms containing volatiles from either M. paniculata or C. sinensis compared to the control arms. When D. citri was exposed to volatiles collected from A. occidentale, they preferred the control arm. Volatiles emitted from the other studied plants did not influence the foraging behaviour of D. citri. Chemical analyses of volatile extracts from C. sinensis, M. paniculata, and A. occidentale revealed the presence of the terpenoids (E)-4,8-dimethylnona-1,3,7-triene (DMNT) and (E,E)-4,8,12-trimethyltrideca-1,3,7,11-tetraene (TMTT) in higher amounts in A. occidentale. In further behavioural bioassays, female D. citri spent less time in arms containing a synthetic blend of DMNT and TMTT compared to the control arms. Female D. citri also spent less time in arms containing the synthetic blend in combination with volatile extracts from either M. paniculata or C. sinensis compared to the control arms. Results suggest that higher release of the two terpenoids by A. occidentale make this species unattractive to D. citri, and that the terpenoids could be used in reducing colonisation of citrus plants and therefore HLB infection.

Conspecific and Heterogeneric Lacewings Respond to (Z)-4-Tridecene Identified from Chrysopa formosa (Neuroptera: Chrysopidae).

Green lacewings (Chrysopidae) are predators of soft-bodied pest insects and are among the most important biological control agents in crop protection. Chrysopa spp. are of special importance since, unlike most green lacewing species, adults are also predatory. The current study was undertaken in search of Chrysopa formosa compounds with semiochemical activity. Using coupled gas chromatography-electroantennography (GC-EAG), head and thorax extracts of C. formosa elicited EAG responses to a compound subsequently identified by coupled GC/mass spectrometry, microchemistry, chemical synthesis and GC peak enhancement as (Z)-4-tridecene. In field experiments, this compound decreased attraction of adult C. formosa to (1R,4aS,7S,7aR)-nepetalactol and that of Chrysoperla carnea species-complex to a ternary floral lure, with the inhibitory effect found to be dose-dependent. Our results suggest that (Z)-4-tridecene may serve as a general warning signal among multiple green lacewing species. Perspectives for potential practical applications are discussed.

cis-Jasmone Elicits Aphid-Induced Stress Signalling in Potatoes.

Elicitation of plant defense signaling that results in altered emission of volatile organic compounds (VOCs) offers opportunities for protecting plants against arthropod pests. In this study, we treated potato, Solanum tuberosum L., with the plant defense elicitor cis-jasmone (CJ), which induces the emission of defense VOCs and thus affects the behavior of herbivores. Using chemical analysis, electrophysiological and behavioral assays with the potato-feeding aphid Macrosiphum euphorbiae, we showed that CJ treatment substantially increased the emission of defense VOCs from potatoes compared to no treatment. Coupled GC-electroantennogram (GC-EAG) recordings from the antennae of M. euphorbiae showed robust responses to 14 compounds present in induced VOCs, suggesting their behavioral role in potato/aphid interactions. Plants treated with CJ and then challenged with M. euphorbiae were most repellent to alate M. euphorbiae. Principal component analysis (PCA) of VOC collections suggested that (E)-2-hexenal, (E,E)-4,8,12-trimethyl-1,3,7,11-tridecatetraene (TMTT), (E)-ß-farnesene, (E)-4,8-dimethyl-1,3,7-nonatriene (DMNT), methyl salicylate (MeSA), CJ, and methyl benzoate (MeBA) were the main VOCs contributing to aphid behavioral responses, and that production of TMTT, (E)-ß-farnesene, CJ, and DMNT correlated most strongly with aphid repellency. Our findings confirm that CJ can enhance potato defense against aphids by inducing production of VOCs involved in aphid-induced signalling.

Electrophysiological and behavioral responses of female African rice gall midge, Orseolia oryzivora Harris and Gagné, to host plant volatiles.

African rice gall midge, Orseolia oryzivora Harris and Gagné, is a major pest of rice in Africa. Depsite its economic importance, its chemical ecology is not well understood. Here, we assessed behavioral and electrophysiological responses of O. oryzivora to host plant volatiles. In olfactometer bioassays, mated female O. oryzivora were attracted to volatiles emitted from intact rice plants but were repelled by volatiles collected from plants infested by conspecifics. In a choice test, there was a preference for volatiles from uninfested plants over those from infested plants. Coupled gas chromatography-electroantennography analyses of panicle volatiles isolated four electrophysiologically active components: (S)-linalool, 4,8-dimethyl-1,3,7-nonatriene, (E)-caryophyllene, and (R/S)-(E)-nerolidol. A synthetic blend of volatiles at the same concentration and ratio as that from an intact plant was attractive to mated females, whereas a blend based on the ratio of volatiles from an infested plant was repellent. This suggests that O. oryzivora uses olfaction for host plant recognition. The identification of blends of volatiles emitted by plants that can both attract and repel O. oryzivora may aid the development of sustainable control measures.