WTV2.0: A high-coverage plant volatilomics method with a comprehensive selective ion monitoring acquisition mode

Volatilomics is essential for understanding the biological functions and fragrance contributions of plant volatiles. However, the annotation coverage of current untargeted and widely-targeted methods has been limited by low sensitivity and/or low acquisition coverage. Here, we introduce WTV 2.0. It enables the construction of a high-coverage library containing 2111 plant volatiles; the development of a comprehensive-selective ion monitoring (cSIM) acquisition method that contains the fewest but sufficient ions for most plant volatiles, including the selection of characteristic qualitative ions with minimal ions number for each compound and the optimized segmentation of acquisition method; and finally, the automatic qualitative and semi-quantitative analysis of cSIM data. Furthermore, the library and acquisition method can be self-expanded by incorporating compounds not present in the library, utilizing the obtained cSIM data. WTV 2.0 increased the median signal-to-noise ratio by 7.6-fold compared to the untargeted method, doubled the annotation coverage compared to the untargeted and WTV 1.0 methods in tomato fruit, and leading to the discovery of menthofuran as a novel flavor compound in passion fruit. WTV 2.0 is a Python library with a user-friendly interface, and is applicable to volatiles and primary metabolites profiling in any species.

Behavioral and molecular response of the insect parasitic nematode Steinernema carpocapsae to plant volatiles

Entomopathogenic nematodes (EPNs) use the chemical cues emitted by insects and insect-damaged plants to locate their hosts. Steinernema carpocapsae, a species of EPN, is an established biocontrol agent used against insect pests. Despite its promising potential, the molecular mechanisms underlying its ability to detect plant volatiles remain poorly understood. In this study, we investigated the response of S. carpocapsae infective juveniles (IJs) to 8 different plant volatiles. Among these, carvone was found to be the most attractive volatile compound. To understand the molecular basis of the response of IJs to carvone, we used RNA-Seq technology to identify gene expression changes in response to carvone treatment. Transcriptome analysis revealed 721 differentially expressed genes (DEGs) between carvone-treated and control groups, with 403 genes being significantly upregulated and 318 genes downregulated. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis showed that the responsive DEGs to carvone attraction were mainly involved in locomotion, localization, behavior, response to stimulus, and olfactory transduction. We also identified four upregulated genes of chemoreceptor and response to stimulus that were involved in the response of IJs to carvone attraction. Our results provide insights into the potential transcriptional mechanisms underlying the response of S. carpocapsae to carvone, which can be utilized to develop environmentally friendly strategies for attracting EPNs.

Many different flowers make a bouquet: Lessons from specialized metabolite diversity in plant-pollinator interactions

Flowering plants have evolved extraordinarily diverse metabolites that underpin the floral visual and olfactory signals enabling plant-pollinator interactions. In some cases, these metabolites also provide unusual rewards that specific pollinators depend on. While some metabolites are shared by most flowering plants, many have evolved in restricted lineages in response to the specific selection pressures encountered within different niches. The latter are designated as specialized metabolites. Recent investigations continue to uncover a growing repertoire of unusual specialized metabolites. Increased accessibility to cutting-edge multi-omics technologies (e.g. genome, transcriptome, proteome, metabolome) is now opening new doors to simultaneously uncover the molecular basis of their synthesis and their evolution across diverse plant lineages. Drawing upon the recent literature, this perspective discusses these aspects and, where known, their ecological and evolutionary relevance. A primer on omics-guided approaches to discover the genetic and biochemical basis of functional specialized metabolites is also provided.

Differential defensive and nutritional traits among cultivated tomato and its wild relatives shape their interactions with a specialist herbivore

Cultivated tomato presented lower constitutive volatiles, reduced morphological and chemical defenses, and increased leaf nutritional quality that affect its resistance against the specialist herbivore Tuta absoluta compared to its wild relatives. Plant domestication process has selected desirable agronomic attributes that can both intentionally and unintentionally compromise other important traits, such as plant defense and nutritional value. However, the effect of domestication on defensive and nutritional traits of plant organs not exposed to selection and the consequent interactions with specialist herbivores are only partly known. Here, we hypothesized that the modern cultivated tomato has reduced levels of constitutive defense and increased levels of nutritional value compared with its wild relatives, and such differences affect the preference and performance of the South American tomato pinworm, Tuta absoluta-an insect pest that co-evolved with tomato. To test this hypothesis, we compared plant volatile emissions, leaf defensive (glandular and non-glandular trichome density, and total phenolic content), and nutritional traits (nitrogen content) among the cultivated tomato Solanum lycopersicum and its wild relatives S. pennellii and S. habrochaites. We also determined the attraction and ovipositional preference of female moths and larval performance on cultivated and wild tomatoes. Volatile emissions were qualitatively and quantitatively different among the cultivated and wild species. Glandular trichomes density and total phenolics were lower in S. lycopersicum. In contrast, this species had a greater non-glandular trichome density and leaf nitrogen content. Female moths were more attracted and consistently laid more eggs on the cultivated S. lycopersicum. Larvae fed on S. lycopersicum leaves had a better performance reaching shorter larval developmental times and increasing the pupal weight compared to those fed on wild tomatoes. Overall, our study documents that agronomic selection for increased yields has altered the defensive and nutritional traits in tomato plants, affecting their resistance to T. absoluta.

Altered volatile emission of pear trees under elevated atmospheric CO2 levels has no relevance to pear psyllid host choice

The impact of climate change drivers on cultivated plants and pest insects has come into research focus. One of the most significant drivers is atmospheric carbon dioxide, which is converted into primary plant metabolites by photosynthesis. Increased atmospheric CO2 concentrations therefore affect plant chemistry. The chemical composition of non-volatile and volatile organic compounds of plants is used by insects to locate and identify suitable host plants for feeding and reproduction. We investigated whether elevated CO2 concentrations in the atmosphere affect the plant-pest interaction in a fruit crop of high economic importance in Europe. Therefore, potted pear trees were cultivated under specified CO2 conditions in a Free-Air Carbon dioxide Enrichment (FACE) facility at Geisenheim University in Germany for up to 14 weeks, beginning from bud swelling. We compared emitted volatiles from these pear trees cultivated for 7 and 14 weeks under two different CO2 levels (ambient: ca. 400 ppm and elevated: ca. 450 ppm CO2) and their impact on pest insect behavior. In total, we detected and analyzed 76 VOCs from pear trees. While we did not detect an overall change in VOC compositions, the relative release of single compounds changed in response to CO2 increase. Differences in VOC release were inconsistent over time (phenology stages) and between study years, indicating interactions with other climate parameters, such as temperature. Even though insect-plant interaction can rely on specific volatile compounds and specific mixtures of compounds, respectively, the changes of VOC patterns in our field study did not impact the host choice behavior of C. pyri females. In olfactometer trials, 64% and 60% of the females preferred the odor of pear trees cultivated under elevated CO2 for 7 and 14 weeks, respectively, over the odor from pear trees cultivated under ambient CO2. In binary-choice oviposition assays, C. pyri females laid most eggs on pears during April 2020; on average, 51.9 (± 51.3) eggs were laid on pears cultivated under eCO2 and 60.3 (± 48.7) eggs on aCO2.

The Role of Herbivore-induced Plant Volatiles in Trophic Interactions: The Swiss Connection

It is increasingly evident that plants actively respond to the threats and challenges that they come to face while growing. This is particularly manifested in the dynamic responses to insect herbivory, especially in terms of the volatile compounds that the attacked plants emit. Indeed, many plants respond to insect-inflicted damage with the synthesis and release of volatile organic compounds. These emissions, commonly referred to as herbivore-induced plant volatiles (HIPVs), play important roles in the interactions between the emitting plants and their biotic environment. The odorous signal can be picked up and exploited by various organisms: neighbouring plants, herbivores and their natural enemies, such as predators and parasitoid wasps. Coincidence or not, scientists currently working in Switzerland have made numerous key contributions to the work in this field. By highlighting their work, we attempt to give a somewhat historic overview of this field of research.

Silver and copper-oxide nanoparticles prepared with GA3 induced defense in rice plants and caused mortalities to the brown planthopper, Nilaparvata lugens (Stål)

BACKGROUND

Nanoparticles have been employed as nanopesticides for pest control in agriculture. However, the harmful effects of their chemical synthesis on human and environmental health have resulted in increased use of green synthetic approaches, including the use of plant extracts. The brown planthopper, Nilaparvata lugens (Stål) (BPH), is a severe pest of rice plants (Oryza sativa L.), especially in Asia. It is usually controlled chemically but has developed resistance against many insecticides.

RESULTS

In this study, we synthesized metallic silver (Ag-NPs) and copper-oxide (CuO-NPs) nanoparticles using the exogenous phytohormone, gibberellic acid (GA₃), as a reducing agent. We then sprayed them separately on rice plants and BPH together and evaluated their effects on the plants and insects. SEM and TEM images showed that the synthesis was successful, indicated by the sizes (25-60 nm), uniform shape and spherical and cubical structures of Ag-NPs, as well as by the rugby sheet-like of CuO-NPs with lateral sizes of 150-340 nm and thickness of 30-70 nm. Independent applications of the nanoparticles and GA₃ on rice plants induced different volatile profiles, of which the highest number emitted was under Ag-NPs, including the highest emission of linalool. Transcriptome analysis showed that Ag-NPs-treated rice plants showed different transcriptome profiles compared to the control, 24 h after treatment, including the upregulation of the linalool synthase gene, genes of plants transcription factors such as WRKY, bHLH and NAC and other genes involved in plant defense responses. In all treatments, the mortality rate of BPH increased with an increase in NPs concentrations over time but was prominent under Ag-NPs treatment. The LC₅₀ values for Ag-NPs and CuO-NPs decreased with an increase in time. Also, the nanoparticles increased the activities of protective enzymes (POD, SOD and CAT), inhibited that of detoxification enzymes (A-CHE, ACP and AKP), and reduced total protein concentrations in the BPH.

CONCLUSIONS

These results show that synthesizing nanoparticles using phytohormones may be a safer and environmentally friendly option, which also holds promise for controlling the BPH in rice production.

Chemical Ecology of the host searching behavior in an Egg Parasitoid: are Common Chemical Cues exploited to locate hosts in Taxonomically Distant Plant Species?

Parasitoids are known to exploit volatile cues emitted by plants after herbivore attack to locate their hosts. Feeding and oviposition of a polyphagous herbivore can induce the emission of odor blends that differ among distant plant species, and parasitoids have evolved an incredible ability to discriminate them and locate their hosts relying on olfactive cues. We evaluated the host searching behavior of the egg parasitoid Cosmocomoidea annulicornis (Ogloblin) (Hymenoptera: Mymaridae) in response to odors emitted by two taxonomically distant host plants, citrus and Johnson grass, after infestation by the sharpshooter Tapajosa rubromarginata (Signoret) (Hemiptera: Cicadellidae), vector of Citrus Variegated Chlorosis. Olfactory response of female parasitoids toward plants with no herbivore damage and plants with feeding damage, oviposition damage, and parasitized eggs was tested in a Y-tube olfactometer. In addition, volatiles released by the two host plant species constitutively and under herbivore attack were characterized. Females of C. annulicornis were able to detect and significantly preferred plants with host eggs, irrespectively of plant species. However, wasps were unable to discriminate between plants with healthy eggs and those with eggs previously parasitized by conspecifics. Analysis of plant volatiles induced after sharpshooter attack showed only two common volatiles between the two plant species, indole and β-caryophyllene. Our results suggest that this parasitoid wasp uses common chemical cues released by many different plants after herbivory at long range and, once on the plant, other more specific chemical cues could trigger the final decision to oviposit.

Priming Seeds with Indole and (Z)-3-Hexenyl Acetate Enhances Resistance Against Herbivores and Stimulates Growth

A striking feature of plant ecology is the ability of plants to detect and respond to environmental cues such as herbivore-induced plant volatiles (HIPVs) by priming or directly activating defenses against future herbivores. However, whether seeds also respond to compounds that are common constituents of HIPV blends and initiate future plant resistance is unknown. Considering that seeds depend on other environmental cues to determine basic survival traits such as germination timing, we predicted that seeds exposed to synthetic constituents of HIPV blends would generate well-defended plants. We investigated the effect of seed exposure to common volatiles on growth, reproduction, and resistance characteristics in the model plants Arabidopsis thaliana and Medicago truncatula using herbivores from two feeding guilds. After seed scarification and vernalization, we treated seeds with one of seven different plant-derived volatile compounds for 24 h. Seeds were then germinated and the resulting plants were assayed for growth, herbivore resistance, and expression of inducible defense genes. Of all the synthetic volatiles tested, indole specifically reduced both beet armyworm growth on A. thaliana and pea aphid fecundity on M. truncatula. The induction of defense genes was not affected by seed exposure to indole in either plant species, indicating that activation of direct resistance rather than inducible resistance is the mechanism by which seed priming operates. Moreover, neither plant species showed any negative effect of seed exposure to any synthetic volatile on vegetative and reproductive growth. Rather, M. truncatula plants derived from seeds exposed to (Z)-3-hexanol and (Z)-3-hexenyl acetate grew larger compared to controls. Our results indicate that seeds are sensitive to specific volatiles in ways that enhance resistance profiles with no apparent costs in terms of growth. Seed priming by HIPVs may represent a novel ecological mechanism of plant-to-plant interactions, with broad potential applications in agriculture and seed conservation.

Plant-insect communication in urban forests: Similarities of plant volatile compositions among tree species (host vs. non-host trees) for alder leaf beetle Agelastica coerulea

Behavior of insects, such as pollination and grazing, is usually determined by biogenic volatile organic compounds (BVOCs). However, particularly in O₃-polluted urban forests, the BVOCs-based plant-insect communication can be disrupted by the reaction of O₃ with leaf-emitted BVOCs, such as between Japanese white birch (Betula platyphylla var. japonica) and a leaf beetle (Agelastica coerulea). To understand plant-insect communication in O₃-polluted environments, it is necessary to identify chemical species of BVOCs that contribute to attractiveness toward insects but are diminished by elevated O₃. In this study, we conducted olfactory response tests and gas chromatography mass spectrometry (GC-MS) analyses to clarify whether there is a similarity of BVOC components among Betulaceae host trees that can explain the attraction of the stenophagous insect A. coerulea. The olfactory response tests indicated that Betulaceae host trees attract A. coerulea via leaf-emitted BVOCs, while there was no preference of the leaf beetles to non-host trees (Sorbus commixta and Morus bombycis). However, GC-MS analyses indicated that the composition of BVOC blends considerably differed among Betulaceae host trees, although alders (Alnus hirsuta and A. japonica) had a similar composition of BVOC blend in each season (June and September) during which the adult leaf beetle is active. A distinct characteristic of the emission from B. platyphylla was that 2-carene and limonene, which are O₃-reactive species, were emitted with a high monoterpene ratio irrespective of the season. Thus, these volatiles and the blend could be expected to lead the disrupted communication found between B. platyphylla and A. coerulea under elevated O₃ in previous field studies. In addition, our results indicated that A. coerulea is attracted to more than one blend within Betulaceae host trees, suggesting that grazing damages can be affected by different host preferences and O₃ reactivity with specific BVOCs in the field. BVOCs-based plant-insect interactions should be further studied in multi-species communities to better understand plant-insect communication in O₃-polluted environments.

Attraction of the Biocontrol Agent, Galerucella placida Towards Volatile Blends of Two Polygonaceae Weeds, Rumex dentatus and Polygonum glabrum

The Polygonaceae weed, Rumex dentatus L. grows in association with wheat, mustard and potato, while Polygonum glabrum Willd. grows in association with rice in India. Both larvae and adults of Galerucella placida Baly (Coleoptera: Chrysomelidae) voraciously consume these weeds. Applications of synthetic herbicides to control weeds are harmful to the environment including beneficial organisms. We propose to find volatile organic compounds (VOCs) from both weeds causing attraction of the biocontrol agent, G. placida, in order to attempt to use the insect as a biological weed control. Behavioral responses of G. placida towards volatile blends characteristic of undamaged (UD), insect-damaged (ID), jasmonic acid-treated (JA) or mechanically-damaged (MD) plants were conducted by Y-tube olfactometer bioassays. Cuminaldehyde was predominant in VOCs of UD R. dentatus, ID P. glabrum, and both JA and MD R. dentatus and P. glabrum. Geraniol was predominant in VOCs of UD P. glabrum, while 1,3-diethylbenzene predominated in VOCs of ID R. dentatus. Females were more attracted towards volatile blends of ID plants compared to UD or JA plants. Females did not show attraction towards volatile blends of JA plants. We identified two bioactive synthetics blends, one comprised of seven compounds - 16.65 µg 1,3-diethylbenzene, 10.72 µg acetophenone, 6.52 µg 2,6-(E,Z)-nonadienal, 2.46 µg 1-nonanol, 4.19 µg decanal, 9.86 µg 4-ethylacetophenone and 3.34 µg 1-hexadecene dissolved in 25 µl CH₂Cl₂ and the other containing five compounds - 2.50 µg 2-octanol, 6.84 µg limonene, 0.64 µg dodecane, 6.63 µg 4-ethylacetophenone and 0.24 µg geranyl acetone dissolved in 25 µl CH₂Cl₂. These two blends of volatile compounds could be used to attract the biocontrol agent during early vegetative period of these two weeds, which could lead to eradication of weeds from crop fields.

The endophytic bacterial entomopathogen Serratia marcescens promotes plant growth and improves resistance against Nilaparvata lugens in rice

Entomopathogenic bacteria are commonly used as biological agents to control different insect pests. However, little is known about the role of bacterial entomopathogens as endophytes in regulating both plant growth and resistance against insect pests. Here, we applied the entomopathogenic bacterium Serratia marcescens S-JS1 via rice seed inoculation and evaluated its effects on host plant growth and resistance against the rice pest Nilaparvata lugens. Furthermore, the induction of defense-related secondary metabolites by the bacterium was assessed by GC-MS/MS. We showed that S-JS1 was able to endophytically colonize the roots and shoots of rice seedlings following seed inoculation. Colonized plants showed increased seed germination (9.4-13.3 %), root (8.2-36.4 %) and shoot lengths (4.1-22.3 %), and root (26.7-69.3 %) and shoot fresh weights (19.0-49.0 %) compared to plants without inoculation. We also identified the production of indole-3-acetic acid by S-JS1, which is likely involved in enhancing rice plant growth. In a two-choice test, N. lugens adults preferred to feed on untreated control plants than on plants treated with S-JS1. In the no-choice feeding tests, the survival of N. lugens nymphs that fed on S-JS1-treated plants was significantly lower than that of nymphs that fed on untreated plants. Additionally, seeds treated with 10⁹ cfu/mL S-JS1 resulted in elevated levels of secondary metabolites, which may be associated with N. lugens resistance in rice plants. Therefore, we suggest that the entomopathogenic bacterium S. marcescens be considered a potentially promising endophyte for use in an innovative strategy for the integrated management of insect pests.

Host plant shift differentially alters olfactory sensitivity in female and male Drosophila mojavensis

Animals may vary in their utilization of plants depending on plant availability, and also on the sex of the animal. Evolutionary adaptations may arise, particularly in specialist animals to the chemistry of the host plants, and these adaptations may differ between the sexes due to differences in their interactions with the plants. Drosophila mojavensis uses different host cacti across its range, and volatile chemicals emitted by the host are the primary cue for host plant identification. In this study, we measured responses of individual olfactory sensory neurons to a large suite of odorants across males and females of the two southern D. mojavensis populations. We show that a switch in host plant is accompanied by changes in the olfactory system, but the effect of this switch is minor compared to that of sex. That is, we observe differences in olfactory receptor neuron specificity and sensitivity to odorants between sexes, and to a lesser extent between populations. The majority of sensory differences are restricted to only three of the 17 sensory neurons measured. Further, we found numerous differences between sexes that only occur within one population, i.e., sex-by-population interactions.

Grass-like plants release general volatile cues attractive for gravid Anopheles gambiae sensu stricto mosquitoes

Background

Understanding the ecology and behaviour of disease vectors, including the olfactory cues used to orient and select hosts and egg-laying sites, are essential for the development of novel, insecticide-free control tools. Selected graminoid plants have been shown to release volatile chemicals attracting malaria vectors; however, whether the attraction is selective to individual plants or more general across genera and families is still unclear.

Methods

To contribute to the current evidence, we implemented bioassays in two-port airflow olfactometers and in large field cages with four live graminoid plant species commonly found associated with malaria vector breeding sites in western Kenya: Cyperus rotundus and C. exaltatus of the Cyperaceae family, and Panicum repens and Cynodon dactylon of the Poaceae family. Additionally, we tested one Poaceae species, Cenchrus setaceus, not usually associated with water. The volatile compounds released in the headspace of the plants were identified using gas chromatography/mass spectrometry.

Results

All five plants attracted gravid vectors, with the odds of a mosquito orienting towards the choice-chamber with the plant in an olfactometer being 2–5 times higher than when no plant was present. This attraction was maintained when tested with free-flying mosquitoes over a longer distance in large field cages, though at lower strength, with the odds of attracting a female 1.5–2.5 times higher when live plants were present than when only water was present in the trap. Cyperus rotundus, previously implicated in connection with an oviposition attractant, consistently elicited the strongest response from gravid vectors. Volatiles regularly detected were limonene, β-pinene, β-elemene and β-caryophyllene, among other common plant compounds previously described in association with odour-orientation of gravid and unfed malaria vectors.

Conclusions

The present study confirms that gravid Anopheles gambiae sensu stricto use chemical cues released from graminoid plants to orientate. These cues are released from a variety of graminoid plant species in both the Cyperaceae and Poaceae family. Given the general nature of these cues, it appears unlikely that they are exclusively used for the location of suitable oviposition sites. The utilization of these chemical cues for attract-and-kill trapping strategies must be explored under natural conditions to investigate their efficiency when in competition with complex interacting natural cues.

Graphical abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13071-021-04939-4.

Avoidance of the Plant Hormone Cis-Jasmone by Aedes aegypti Depends On Mosquito Age in Both Plant and Human Odor Backgrounds

Adults of many mosquito species feed on plants to obtain metabolic energy and to enhance reproduction. Mosquitoes primarily rely on olfaction to locate plants and are known to respond to a range of plant volatiles. We studied the olfactory response of the yellow fever mosquito Aedes aegypti to methyl jasmonate (MeJA) and cis-jasmone (CiJA), volatile compounds originating from the octadecanoid signaling pathway that plays a key role in plant defense against herbivores. Specifically, we investigated how Ae. aegypti of different ages responded to elevated levels of CiJA in two attractive odor contexts, either derived from Lima bean plants or human skin. Aedes aegypti females landed significantly less often on a surface with CiJA and MeJA compared to the solvent control, CiJA exerting a stronger reduction in landing than MeJA. Odor context (plant or human) had no significant main effect on the olfactory responses of Ae. aegypti females to CiJA. Mosquito age significantly affected the olfactory response, older females (7–9 d) responding more strongly to elevated levels of CiJA than young females (1–3 d) in either odor context. Our results show that avoidance of CiJA by Ae. aegypti is independent of odor background, suggesting that jasmonates are inherently aversive cues to these mosquitoes. We propose that avoidance of plants with elevated levels of jasmonates is adaptive to mosquitoes to reduce the risk of encountering predators that is higher on these plants, i.e. by avoiding ‘enemy-dense-space’.

Chemical Ecology of the Asian Longhorn Beetle, Anoplophora glabripennis

The Asian longhorn beetle (ALB), Anoplophora glabripennis (Motschulsky), is a destructive forest pest in its native range, East Asia, or a high-risk invasive species in many other parts of the world. Extensive research has been directed toward the development of ALB management strategies. However, semiochemical-based trap lures, which are one of the effective tools for detecting, monitoring, and potentially assisting in eradicating cerambycids, have not reached operational efficacy for ALB to date, which is probably due to a grossly incomplete understanding of its chemical ecology. Here, we summarize the current progress in ALB chemical ecology including host selection and location, pheromone identification, trapping techniques, olfactory system, and related biology and behavior. We also briefly review the known semiochemicals in the subfamily Lamiinae, particularly the ALB congener, A. chinensis. Based on this knowledge, we highlight a potentially important role of some host-original chemicals, such as sesquiterpenes, in ALB host and mate location, and emphasize the basic studies on the biology and behavior of adult ALB. Last, we formulate suggestions for further research directions that may contribute to a better understanding of ALB chemical ecology and improved lure efficacy.

Meaningful Words in Crowd Noise: Searching for Volatiles Relevant to Carpenter Bees among the Diverse Scent Blends of Bee Flowers

Olfactory cues constitute one of the most important plant-pollinator communication channels. Specific chemical components can be associated with specific pollinator functional groups due to pollinator-mediated selection on flower volatile (FV) emission. Here, we used multivariate analyses of FV data to detect an association between FVs and the worldwide distributed pollinator group of the carpenter bees (Xylocopa spp.). We compiled FVs of 29 plant species: 9 pollinated by carpenter bees, 20 pollinated by other bee pollinator functional groups. We tested whether FV emission differed between these groups. To rule out any phylogenetic bias in our dataset, we tested FV emission for phylogenetic signal. Finally, using field assays, we tested the attractive function of two FVs found to be associated with carpenter bees. We found no significant multivariate difference between the two plant groups FVs. However, seven FVs (five apocarotenoid terpenoids, one long-chain alkane and one benzenoid) were significantly associated with carpenter bee pollination, thus being "predictor" compounds of pollination by this pollinator functional group. From those, β-ionone and (E)-methyl cinnamate presented the highest indicator values and had their behavioural function assessed in field assays. Phylogenetic signal for FVs emission was weak, suggesting that their emission could result from pollinator-mediated selection. In field assays, the apocarotenoid β-ionone attracted carpenter bees, but also bees from other functional groups. The benzenoid (E)-methyl cinnamate did not attract significant numbers of pollinators. Thus, β-ionone functions as a non-specific bee attractant, while apocarotenoid FVs emerge as consistent indicators of pollination by large food-foraging bees among bee-pollinated flowers.

Chemically-mediated colonization of black cherry by the peach bark beetle, Phloeotribus liminaris

The peach bark beetle (Phloeotribus liminaris Harris, PBB) affects the health, quality, and value of black cherry (Prunus serotina Ehrh.) within the Central Hardwoods Forest Region of North America. When colonized by adult beetles, black cherry trees produce a defensive exudate, or 'gum', staining the wood and decreasing its value up to 90%. Current management tactics are inadequate to avoid extensive damage to most veneer-sized black cherry in the region. We test the hypothesis that PBB colonization behavior is chemically-mediated and determine the extent to which PBB is attracted to compounds associated with wounded or PBB-infested cherry wood. Through olfactometer and field bioassays, we determined that adult PBB were attracted to cherry branches infested with female beetles. We then used dynamic headspace sampling to collect volatiles associated with wounded and infested bolts of black cherry. The volatile benzaldehyde dominated these collections and was more abundant in aerations of female-infested bolts than other odor sources. In subsequent field bioassays, we evaluated the bioactivity of benzaldehyde, as well as α-longipinene, in combination with several chemical carriers. Traps baited with benzaldehyde captured more PBB than all other treatments, irrespective of other lure components. Moreover, PBB were not attracted to traps baited solely with ethanol, a common attractant for bark beetles that colonize hardwood trees. This is the first report of benzaldehyde as an attractant for a species of bark beetle and could aid in developing semiochemical-based management tactics for this important pest.

Effect of Leaf Maturity on Host Habitat Location by the Egg-Larval Parasitoid Ascogaster reticulata

Adoxophyes honmai, a serious pest of tea plants, prefers to lay eggs on mature tea leaves rather than young leaves. Here, we examined a hypothesis that Ascogaster reticulata, an egg-larval parasitoid of A. honmai, increases the likelihood of encountering host egg masses by searching mature tea leaves when host-derived cues are not available. In a dual-choice bioassay using a four-arm olfactometer, A. reticulata preferred odor from intact, mature leaves versus young leaves. Based on volatile analysis with gas chromatography-mass spectrometry (GC-MS), we identified 5 and 10 compounds from mature and young leaf volatiles, respectively. The 5 components in the extract from intact mature leaves included (Z)-3-hexenyl acetate, (E)-β-ocimene, linalool, (E)-4,8-dimethyl-1,3,7-nonatriene (DMNT), and methyl salicylate. When each individual compound, or quaternary and quintenary blends of them, ratios of which were adjusted to match those of mature leaf volatiles, were provided, parasitoids preferred the full mixture and the quaternary blend devoid of DMNT to the solvent control. Methyl salicylate, one of the components of preferred blends, was not detected among young leaf volatiles. We concluded that the volatile composition of tea leaves changes, depending on their maturity, and that this composition affects foraging behavior of the parasitoid, which is closely related to the host herbivore's oviposition preference.

Multiple Attack to Inflorescences of an Annual Plant Does Not Interfere with the Attraction of Parasitoids and Pollinators

Plants in the flowering stage need to ensure reproduction by protecting themselves from attack and by preserving interactions with mutualist pollinators. When different plant mutualists are using the same type of cues, such as volatile compounds, attraction of parasitoids and pollinators may trade off. To explore this, we compared volatile emission of Brassica nigra plants in response to single or dual attack on their inflorescences. Additionally, we recorded flower visitation by pollinators and the attraction of parasitoids in the greenhouse and/or field. Brassica nigra were exposed in the flowering stage to one or two of the following three attackers: Brevicoryne brassicae aphids, Pieris brassicae caterpillars, and Xanthomonas campestris pv. raphani bacteria. We found that single attack by caterpillars, and dual attack by caterpillars plus aphids, induced the strongest changes in plant volatile emission. The caterpillars’ parasitoid C. glomerata did not exhibit preference for plants exposed to caterpillars only vs. plants exposed to caterpillars plus aphids or plus bacteria. However, the composition of the pollinator community associated with flowers of B. nigra was affected by plant exposure to the attackers, but the total number of pollinators visiting the plants did not change upon attack. We conclude that, when B. nigra were exposed to single or dual attack on their inflorescences, the plants maintained interactions with natural enemies of the insect attackers and with pollinators. We discuss how chemical diversity may contribute to plant resilience upon attack.

Plant Volatiles Modulate Seasonal Dynamics between Hosts of the Polyphagous Mirid Bug Apolygus lucorum

Plant-derived volatiles play a significant role in host selection of phytophagous insects, but their role in seasonal host shifts remain unclear. The polyphagous mirid bug Apolygus lucorum displays marked seasonal host alternation. During summer, volatiles from flowering plants play a key role in A. lucorum foraging. Though A. lucorum adults deposit overwintering eggs on jujube (Ziziphus jujuba) and grape (Vitis vinifera) during autumn, it is unclear whether plant volatiles equally mediate this host selection behavior. During 2015 and 2016, we found that population densities of A. lucorum adults on cotton (Gossypium hirsutum) during August were higher than those in September, whereas the opposite pattern was observed on fruit trees (i.e., jujube and grape). The dispersal factor of the adult population that dispersed from cotton fields during September was higher than in August, whereas opposite patterns were observed in the neighboring jujube/grape orchard. In Y-tube olfactometer trials, A. lucorum adults preferred cotton plant volatiles over fruit tree odors in August, whereas the opposite patterns were found in September. Three electro-physiologically active volatiles (butyl acrylate, butyl propionate and butyl butyrate) were identified from jujube and grape plants. During September, active volatiles are emitted in considerably greater amounts by jujube and grape than in August, while the amount of volatile emissions in cotton decreases in September. Temporal shifts in plant volatile emission thus may modulate host plant foraging of A. lucorum, and appear to guide its colonization of different host plants. Our findings help understand the role of plant volatiles in the host plant selection and seasonal dynamics of polyphagous herbivores.

Morphological characterization of antennal sensilla of Earias vittella (Fabricius) (Lepidoptera: Nolidae)

The shoot and fruit borer, Earias vittella Fab. (Lepidoptera: Nolidae) is an important and most devastating insect pest on okra and cotton. The pest mainly responsible for causing significant direct damage to tender shoots and fruits of okra, flowers and green bolls of cotton causing net yield loss in both crops. Many non-chemical control strategies have been developed under the insect pest management program, A complete knowledge on the antennal morphology of E. vitella is essential for future electrophysiological and behavioural studies. In the present study, the antennal morphology and types of sensilla on the antennae of both sexes of E. vitella were examined using light and scanning electron microscopy. Nine distinct types of sensilla were identified on the antennae of both sexes: sensilla trichodea, sensilla basiconica, sensilla coeloconica, sensilla auricillica (multiporous), sensilla chaetica, uniporous peg sensilla (uniporous), sensilla styloconica, sensilla squamiformia and bohm bristles (aporous). Among all sensilla, the most widespread are multiporous sensilla trichodea with 42.90 ± 1.77/flagellomere in male and 37.38 ± 1.38/flagellomere in female. Sensilla basiconica were the second most common sensillum type in male antennae with 15.67 ± 1.92/flagellomere. Other multiporous sensilla such as auricillica (11.90 ± 0.99) and coeloconica (4.57 ± 0.25) were significantly more abundant in female than in male antennae. Results of the study provide morphological evidence that E. vitella antennae possess microscopic cuticular structures that can play a role in perception of pheromones, plant odours and other chemical stimulants. This will open up opportunities to assess the possibility of using pheromones and plant-derived compounds for the monitoring or management of E. vittella moths in the agricultural landscapes.

The phytotoxic air-pollutant O3 enhances the emission of herbivore-induced volatile organic compounds (VOCs) and affects the susceptibility of black mustard plants to pest attack

Stress-induced changes to plant biochemistry and physiology can influence plant nutritional quality and subsequent interactions with herbivorous pests. However, the effects of stress combinations are unpredictable and differ to the effects of individual stressors. Here we studied the effects of exposure to the phytotoxic air-pollutant ozone (O₃), feeding by larvae of the large cabbage white butterfly (Pieris brassicae), and a combination of the two stresses, on the emission of volatile organic compounds (VOCs) by black mustard plants (Brassica nigra) under field and laboratory conditions. Field-grown B. nigra plants were also measured for carbon-nitrogen (C-N) content, net photosynthetic activity (Pn), stomatal conductance (gs) and biomass. The effects of O₃ on interactions between plants and a herbivorous pest were addressed by monitoring the abundance of wild diamondback moth larvae (Plutella xylostella) and feeding-damage to B. nigra plants in an O₃-free air concentration enrichment (O₃-FACE) field site. Herbivore-feeding induced the emission of VOCs that were not emitted by undamaged plants, both under field and laboratory conditions. The combination of O₃ and herbivore-feeding stresses resulted in enhanced emission rates of several VOCs from field-grown plants. Short-term O₃ exposure (of 10 days) and P. brassicae-feeding did not affect C-N content, but chronic O₃ exposure (of 34 and 47 days) and P. brassicae-feeding exacerbated suppression of Pn. Ozone exposure also caused visible injury and decreased the plant biomass. Field-grown B. nigra under elevated O₃ were infested with fewer P. xylostella larvae and received significantly less feeding damage. Our results suggest that plants growing in a moderately polluted environment may be of reduced quality and less attractive to foraging herbivores.

Spontaneous emission of volatiles from the male flowers of the early-branching angiosperm Amborella trichopoda

Volatile emissions were detected for the first time in male flowers of the early-branching angiosperm Amborella trichopoda, suggesting a defensive and attractive double role of these compounds. Flower volatile emissions were detected for the first time in male flowers of the early-branching angiosperm Amborella trichopoda. A mixture of seven volatile compounds is found in flower buds, with limonene resulting as the most abundant compound (67%). Further five volatiles are found in freshly opened flowers, with limonene contributing to 31.7%, followed by decanal (15.5%) and by ethyl octanoate (10.3%). While monoterpene hydrocarbons dominate in flower buds (73.6%), their emission in freshly opened flowers is reduced to 41.1%, while non-terpene derivatives are the most abundant (47.1%) chemical class. These compounds, emitted in low amounts, are possibly linked to pollen, which is considered the only reward offered for insect-pollination in this species.

Plant odors trigger clearing behavior in foraging trails- do they represent olfactory obstacles?

Foraging trails of leaf-cutting ants may be exposed to plant material that interferes with foragers' flux either by physically blocking it or due to secondary metabolites which affect insect behavior. We hypothesized that plant secondary metabolites such as plant volatiles may interfere with pheromone communication, triggering clearing behavior. We impregnated small pieces of paper with different plant odors from native and exotic species and placed them in the middle of foraging trails of the leaf-cutting ant Acromyrmex lobicornis. As a control, we used papers impregnated with trail odor. The paper used as substrate for the odors did not constitute a physical obstacle based on its small surface area. Papers treated with trail odor did not interfere with ant flux and were not removed from the trail. However, when papers were treated with plant odors, they were removed from the trail in most of the cases and ant flux was reduced significantly by 15-28%. We found that ants tapped the tip of their gaster against the ground around the treated papers only when they were impregnated with foreign odors. The number of gaster tappings as well as the time between the placement of the paper and its removal increased with plant odor concentration. However, the decision to remove the paper was not correlated with the number of gaster tappings. Interestingly, clearer ants were smaller than forager ants, suggesting there is morphological differentiation in clearing behavior of the trail. Results from the current study also suggest that odors trigger clearing behavior on foraging trails and affect trail marking behavior. Our results provide information about the potential for plant compounds to constitute obstacles, even when they do not physically obstruct the trail. We conclude that odors may trigger clearing behavior by interfering with pheromone communication.

Molecular Screening of Behaviorally Active Compounds with CmedOBP14 from the Rice Leaf Folder Cnaphalocrocis medinalis

Odorant binding proteins (OBPs) play a key role in chemoreception in insects. In an earlier study, we identified CmedOBP14 from the rice leaf folder, Cnaphalocrocis medinalis, with potential physiological functions in olfaction. Here, we performed a competitive binding assay under different pH conditions as well as knockdown via RNA interference to determine the specific role of CmedOBP14 in C. medinalis. CmedOBP14 displayed broad binding affinities to many host-related compounds, with higher affinities at pH 7.4 compared with pH 5.0. After treatment with CmedOBP14-dsRNA, the transcript level of OBP14 was significantly decreased at 72 h compared with controls, and the electroantennogram response evoked by nerolidol, L-limonene and beta-ionone was reduced. Furthermore, behavioral assays revealed consistent patterns among these compounds, especially for nerolidol, with adults could no longer able to differentiate 0.1% nerolidol from controls. RNAi experiments suggest that at least in part, CmedOBP14 mediates the ability to smell nerolidol and beta-ionone.

Synergistic Effects of Volatiles from Host-Infested Plants on Host-Searching Behavior in the Parasitoid Wasp Lytopylus rufipes (Hymenoptera: Braconidae)

Herbivore-induced plant volatiles (HIPVs) are important cues for natural enemies to find their hosts. HIPVs are usually present as blends and the effects of combinations of individual components are less studied. Here, we investigated plant volatiles in a tritrophic system, comprising the parasitoid wasp Lytopylus rufipes Nees (Hymenoptera: Braconidae), the Oriental fruit moth Grapholita molesta (Busck) (Lepidoptera: Tortricidae), and Japanese pear, Pyrus pyrifolia 'Kosui', so as to elucidate the effects of single components and blends on wasp behaviors. Bioassays in a four-arm olfactometer, using either shoots or their isolated volatiles collected on adsorbent, revealed that female wasps preferred volatiles from host-infested shoots over those from intact shoots. Analyses identified (Z)-3-hexenyl acetate (H), linalool (L), (E)-β-ocimene (O), (E)-3,8-dimethyl-1,4,7-nonatriene (D), and (E,E)-α-farnesene (F). Among them, only F was induced by infestation with G. molesta. When tested singly, only O and D elicited positive responses by L. rufipes. Binary blends of HO and DF elicited a positive response, but that of HD elicited a negative one, even though D alone elicited a positive response. Remarkably, wasps did not prefer either the ODF or HL blends, but showed a highest positive response to a quinary blend (HLODF). These results show that synergism among volatiles released from host-infested plants is necessary for eliciting high behavioral responses in L. rufipes, enabling L. rufipes to find its host efficiently.

Herbivore-Induced Volatiles from Maize Plants Attract Chelonus insularis, an Egg-Larval Parasitoid of the Fall Armyworm

Chelonus insularis (Hymenoptera: Braconidae) is an egg-larval endoparasitoid that attacks several lepidopteran species, including the fall armyworm (FAW), Spodoptera frugiperda, as one of its main hosts. In this study, we identified the volatiles emitted by maize plants undamaged and damaged by S. frugiperda larvae that were attractive to virgin C. insularis females. In a Y-glass tube olfactometer, parasitoid females were more attracted to activated charcoal extracts than Porapak Q maize extracts. Chemical analysis of activated charcoal extracts from maize plants damaged by S. frugiperda larvae by gas chromatography coupled with electroantennography (GC-EAD) showed that the antennae of virgin female wasps consistently responded to three compounds, identified by gas chromatography-mass spectrometry (GC-MS) as α-pinene, α-longipinene and α-copaene. These compounds are constitutively released by maize plants but induction via herbivory affects their emissions. α-Longipinene and α-copaene were more abundant in damaged maize plants than in healthy ones, whereas α-pinene was produced in higher amounts in healthy maize plants than in damaged ones. Female parasitoids were not attracted to EAD-active compounds when evaluated singly; however, they were attracted to the binary blend α-pinene + α-copaene, which was the most attractive blend, even more attractive than the tertiary blend (α-pinene + α-longipinene + α-copaene) and the damaged maize plant extracts. We conclude that C. insularis is attracted to a blend of herbivore-induced volatiles emitted by maize plants.

An Inexpensive and Comprehensive Method to Examine and Quantify Field Insect Community Influenced by Host Plant Olfactory Cues

Insect pollinators, herbivores and their natural enemies use olfactory cues emitted by their host plants to locate them. In insect-plant ecology, understanding the mechanisms underlying these interactions are of critical importance, as this bio-communication has both ecological and agricultural applications. However, the first step in such research is to identify and quantify the insect community associated with the plant/s species of interest. Traditionally, this has been accomplished by a variety of insect trapping methods, either using pitfall traps, or sticky traps, or sweep nets in field. The data collected from these traps tend to be incomplete, and also damage the specimens, making them unusable for any taxonomic purposes. This protocol derives ideas from these traditional traps and use a combination of three easily made inexpensive modified traps that conceals the host plant, but allows the plant volatiles to pass through as olfactory cues. These traps are economical, can be made to fit with most plant sizes, and are also reusable. Collectively, these traps will provide a solid estimate (quantifiable) of all associated community of arthropods that can also be stored for future studies.

Expressional and functional comparisons of two general odorant binding proteins in Agrotis ipsilon

Insect general odorant binding proteins (GOBPs) have been long thought to bind and transport host plant volatiles to the olfactory receptors on the dendrite membrane of the olfactory neurons. Recent studies indicate that they can also bind female sex pheromones. In present study, two GOBP genes, AipsGOBP1 and AipsGOBP2 were cloned from the adult antennae of Agrotis ipsilon. Tissue expression profiles indicated that both of them are antennae-specific and more abundant in the female antennae than in the male antennae. Temporal expression profiles showed that both AipsGOBP1 and AipsGOBP2 began to express in antennae 3 days prior to adult emergence from pupae, and reached their highest expression level 3 and 4 days after adult emergence, respectively. Mating increased their expression in the female antennae but reduced their expression in the male antennae. In situ hybridization and immunolocalization demonstrated that both AipsGOBP1 and AipsGOBP2 are expressed and co-localized in sensilla basiconica and sensilla trichodea of both sexes. AipsGOBP2 exhibited a high binding affinity in vitro with the two major sex pheromone components Z7-12:Ac and Z9-14:Ac and the four plant volatiles cis-3-hexen-1-ol, oleic acid, dibutyl phthalate and β-caryophyllene with Ki values less than 5 μM. AipsGOBP1, on the other hand, showed medium binding affinities with the five A. ipsilon sex pheromones and six plant volatiles. AipsGOBP2 also showed a broader ligand-binding spectrum and a greater ligand-binding affinity than AipsGOBP1 with the tested aldehyde and alcohol sex pheromones of Lepidoptera species. Taken together, our results indicate that AipsGOBP2 may play greater roles than AipsGOBP1 does in binding sex pheromones and host plant volatiles.

Olfactory Sensory Neurons of the Asian Longhorned Beetle, Anoplophora glabripennis, Specifically Responsive to its two Aggregation-Sex Pheromone Components

We performed single-sensillum recordings from male and female antennae of the Asian longhorned beetle, Anoplophora glabripennis, that included as stimuli the two components of this species' aggregation-sex pheromone in addition to various general odorants. We compared the aggregation-sex-pheromone-component responses of olfactory sensory neurons (OSNs) to those of OSNs that responded to a variety of plant-related odorants. In the smooth-tipped, tapered, trichoid sensilla on the most distal antennal flagellomeres nos. 10 or 11 of both males and females, we found OSNs with high-amplitude action potentials that were tuned to the aldehyde and alcohol pheromone components and that did not respond to various plant-related volatiles. Because this OSN type responded to both the alcohol and aldehyde components it cannot be considered to be specifically tuned to either component. These large-spiking OSNs were co-compartmentalized in these sensilla with a second, smaller-spiking OSN responding to plant-related volatiles such as geraniol, citronellal, limonene, 1-octanol, nerol and citral. The large-spiking OSNs thus appear to be a type that will be involved in aggregation-sex pheromone pathways targeting a specific glomerulus in the antennal lobe and in generating pheromone-related behavioral responses in A. glabripennis. In other sensilla located in these distal antennal flagellomeres as well as those located more proximally, i.e., mid-length along the antenna on flagellomere nos. 4-7, we found OSNs in blunt-tipped basiconic sensilla that were responsive to other plant-related volatiles, especially the terpenoids, (E,E)-alpha farnesene, (E)-β-farnesene, β-caryophyllene, and eugenol. Some of these terpenoids have been implicated in improving attraction to pheromone-baited traps. Some of these same OSNs responded additionally to either of the two sex pheromone components, but because these OSNs also responded to some of the above plant volatiles as shown by cross-adaptation experiments, these OSNs will not be the types that convey sex-pheromone-specific information to the antennal lobe.

Role of Plant Volatiles in Host Plant Recognition by Listronotus maculicollis (Coleoptera: Curculionidae)

The annual bluegrass weevil (ABW), Listronotus maculicollis Kirby, is an economically important pest of short cut turfgrass. Annual bluegrass, Poa annua L., is the most preferred and suitable host for ABW oviposition, larval survival and development. We investigated the involvement of grass volatiles in ABW host plant preference under laboratory and field conditions. First, ovipositional and feeding preferences of ABW adults were studied in a sensory deprivation experiment. Clear evidence of involvement of olfaction in host recognition by ABW was demonstrated. Poa annua was preferred for oviposition over three bentgrasses, Agrostis spp., but weevils with blocked antennae did not exhibit significant preferences. ABW behavioral responses to volatiles emitted by Agrostis spp. and P. annua were examined in Y-tube olfactometer assays. Poa annua was attractive to ABW females and preferred to Agrostis spp. cultivars in Y-tube assays. Headspace volatiles emitted by P. annua and four cultivars of Agrostis stolonifera L. and two each of A. capillaris L. and A. canina L. were extracted, identified and compared. No P. annua specific volatiles were found, but Agrostis spp. tended to have larger quantities of terpenoids than P. annua. (Z)-3-hexenyl acetate, phenyl ethyl alcohol and their combination were the most attractive compounds to ABW females in laboratory Y-tube assays. The combination of these compounds as a trap bait in field experiments attracted adults during the spring migration, but was ineffective once the adults were on the short-mown turfgrass. Hence, their usefulness for monitoring weevil populations needs further investigation.

A biosynthetically informed distance measure to compare secondary metabolite profiles

Secondary metabolite profiles are one of the most diverse phenotypes of organisms and can consist of a large number of compounds originating from a limited number of biosynthetic pathways. The statistical treatment of such profiles often is complicated due to their diversity as well as the intra- and interspecific variability in the quantitative and qualitative composition of secondary metabolites. Most importantly, the assumption of independence of the presence/absence and the quantity of compounds is violated due to the shared biosynthetic origin of many compounds. Therefore, I propose a biosynthetically informed pairwise distance measure that fully considers the biosynthesis of the compounds and thus quantifies the similarity in the enzymatic equipment of two samples. The biosynthetic similarity of compounds is calculated based on the proportion of shared enzymes that are required for their biosynthesis. Using this information (provided as dendrogram structure) and the quantitative composition of the samples, generalized UniFrac distances are calculated measuring that fraction of the dendrogram (i.e., the branch lengths) that is unique to either of the samples but not shared by both samples. To allow a straightforward cross-platform application of the approach, I provide functions for the statistical software R and sample data sets. A hypothetical and a real world example show the feasibility of the biosynthetically informed distances dA,B and highlight the differences to conventional distance measures. The advantages of this approach and potential fields of application are discussed.

Antennal and behavioral responses of Mythimna separata (Walker) to three plant volatiles

The oriental armyworm, Mythimna separata, is distributed widely in eastern Asia and Australia. The response of M.separata to 27 compounds identified from plant volatiles was determined from electroantennography (EAG) and wind tunnel results, which allowed an evaluation of the possible plant volatile compounds. The highest EAG values of males were elicited by trans-2,cis-6-nonadienal, and virgin females by benzyl alcohol. The amplitude in EAG dose-response was in the range of 0.24 to 2.87 mV. In the wind tunnel bioassays, significantly more females showed behavioral responses to wilting leaves and headspace collection of Pterocarya stenoptera rather than control. In addition, significantly more females flew upwind with beta-ocimene compared with the control. The number of females that landed at the source with cis-3-hexen-1-ol, phenylethyl alcohol, trans-2-nonenal, and 2-pentylfuran was significantly different from the number that moved towards control.

Host Plant Species Differentiation in a Polyphagous Moth: Olfaction is Enough

Polyphagous herbivorous insects need to discriminate suitable from unsuitable host plants in complex plant communities. While studies on the olfactory system of monophagous herbivores have revealed close adaptations to their host plant's characteristic volatiles, such adaptive fine-tuning is not possible when a large diversity of plants is suitable. Instead, the available literature on polyphagous herbivore preferences suggests a higher level of plasticity, and a bias towards previously experienced plant species. It is therefore necessary to take into account the diversity of plant odors that polyphagous herbivores encounter in the wild in order to unravel the olfactory basis of their host plant choice behaviour. In this study we show that a polyphagous moth, Spodoptera littoralis, has the sensory ability to distinguish five host plant species using olfaction alone, this being a prerequisite to the ability to make a choice. We have used gas chromatography mass spectrometry (GC-MS) and gas chromatography electroantennographic detection (GC-EAD) in order to describe host plant odor profiles as perceived by S. littoralis. We find that each plant emits specific combinations and proportions of GC-EAD active volatiles, leading to statistically distinct profiles. In addition, at least four of these plants show GC-EAD active compound proportions that are conserved across individual plants, a characteristic that enables insects to act upon previous olfactory experiences during host plant choice. By identifying the volatiles involved in olfactory differentiation of alternative host plants by Spodoptera littoralis, we set the groundwork for deeper investigations of how olfactory perceptions translate into behaviour in polyphagous herbivores.

Identification of the Aggregation-sex Pheromone Produced by Male Monochamus saltuarius, a Major Insect Vector of the Pine Wood Nematode

In this study, we isolated and identified an aggregation-sex pheromone from Monochamus saltuarius, the major insect vector of the pine wood nematode in Korea. Adult males of M. saltuarius produce 2-undecyloxy-1-ethanol, which is known as an aggregation-sex pheromone in other Monochamus species. We performed field experiments to determine the attractiveness of the pheromone and other synergists. More M. saltuarius adult beetles were attracted to traps baited with the pheromone than to unbaited traps. Ethanol and (-)-α-pinene interacted synergistically with the pheromone. Traps baited with the pheromone + (-)-α-pinene +ethanol were more attractive to M. saltuarius adults than traps baited with the pheromone, (-)-α-pinene, or ethanol alone. Ipsenol, ipsdienol, and limonene were also identified as synergists of the aggregation-sex pheromone for M. saltuarius adults. In field experiments, the proportion of females was much higher in the beetles caught in traps than among the beetles emerging from naturally-infested logs in the laboratory. Our results suggest that a combination of aggregation-sex pheromone and synergists could be very effective for monitoring and managing M. saltuarius.

Synthetic Co-Attractants of the Aggregation Pheromone of the Date Palm Root Borer Oryctes agamemnon

Laboratory and field investigations to identify and evaluate plant co-attractants of the aggregation pheromone of the date palm pest Oryctes agamemnon are reported. Volatiles emitted by freshly cut palm core and palm core with feeding males, were collected, analyzed by gas chromatography coupled to mass spectrometry and evaluated in olfactometers alone or combined with synthetic pheromone. A collection of palm odor without male effluvia was attractive alone and enhanced attraction to synthetic pheromone in an olfactometer similar to that to a collection of palm odor emitted with feeding males and containing natural pheromone. Behavioral responses to collections of palm volatiles were correlated to the amount of volatiles material in them. Enhancement of the attractiveness of the pheromone was not correlated to chemicals specific to beetle feeding. The chemicals common to the active collections extracts were benzoate esters, mostly ethyl benzoate, anisole derivatives and sesquiterpenes. Blends of the most abundant components of the extracts were evaluated for enhancement of the attractiveness of pheromone (1 μg) in olfactometers at 1 or 10 μg doses. The mixtures were further evaluated by field trapping in Tunisia at 3-10 mg/day using reference (6 mg/day) or experimental pheromone formulations. A mixture of ethyl benzoate, 4-methylanisole and farnesol (1:1:1 w/w at 6.5 mg/day) enhanced captures in pheromone baited traps in 2014 and 2015 and this mixture was as active as the natural palm bait. The practical prospect of the result for the management for O. agamemnon, and other palm beetles is discussed.

Does Aphid Infestation Interfere with Indirect Plant Defense against Lepidopteran Caterpillars in Wild Cabbage?

Attraction of parasitoids to plant volatiles induced by multiple herbivory depends on the specific combinations of attacking herbivore species, especially when their feeding modes activate different defense signalling pathways as has been reported for phloem feeding aphids and tissue feeding caterpillars. We studied the effects of pre-infestation with non-host aphids (Brevicoryne brassicae) for two different time periods on the ability of two parasitoid species to discriminate between volatiles emitted by plants infested by host caterpillars alone and those emitted by plants infested with host caterpillars plus aphids. Using plants originating from three chemically distinct wild cabbage (Brassica oleracea) populations, Diadegma semiclausum switched preference for dually infested plants to preference for plants infested with Plutella xylostella hosts alone when the duration of pre-aphid infestation doubled from 7 to 14 days. Microplitis mediator, a parasitoid of Mamestra brassicae caterpillars, preferred dually-infested plants irrespective of aphid-infestation duration. Separation of the volatile blends emitted by plants infested with hosts plus aphids or with hosts only was poor, based on multivariate statistics. However, emission rates of individual compounds were often reduced in plants infested with aphids plus hosts compared to those emitted by plants infested with hosts alone. This effect depended on host caterpillar species and plant population and was little affected by aphid infestation duration. Thus, the interactive effect of aphids and hosts on plant volatile production and parasitoid attraction can be dynamic and parasitoid specific. The characteristics of the multi-component volatile blends that determine parasitoid attraction are too complex to be deduced from simple correlative statistical analyses.

Volatile-Mediated Interactions between Cabbage Plants in the Field and the Impact of Ozone Pollution

Plants constitutively release volatile organic compounds (VOCs), but qualitatively and quantitatively alter their emission of VOCs in response to biotic and abiotic stresses. The blend of VOCs emitted reflects the physiological status of the plant. Plants may be exposed to the VOC blend emitted by their near neighbors and gain information that allows them to adjust their own defenses. These plant-plant interactions may potentially be exploited to protect crops from pests, but they can be disturbed by abiotic factors making the process sensitive to environmental perturbation. Despite numerous studies describing plant-plant interactions, relatively few have been conducted with agriculturally significant cultivated plant varieties under field conditions. Here we studied plant-plant interactions in a conspecific association of Brassica oleracea var. capitata (cabbage) and show that undamaged plants exposed to neighbors damaged by the herbivore Pieris brassicae are primed for stronger volatile emissions upon subsequent herbivore attack. We conducted a field study in an ozone free-air concentration enrichment (FACE) facility with ambient and elevated ozone levels and found that elevated tropospheric ozone significantly alters the priming of VOCs in receiver plants. We conclude that plant-plant interactions may prime defensive attributes of receiver plants under field conditions, but are impaired by ozone pollution. Therefore, when planning the manipulation of plant-plant interactions for agricultural purposes, the potential effects of atmospheric pollutants should be considered.

Non-Target Impacts of an Attract-and-Kill Formulation Based on Plant Volatiles: Responses of some Generalist Predators

Responses of non-target insects to a blend of plant volatiles used as components in an attract-and-kill formulation for Helicoverpa spp. (Lepidoptera: Noctuidae) were studied in an Australian cotton field. Two experiments, one involving suction sampling during the day and the other at night, were conducted. Rows that had been treated with the volatile blend, with no added insecticide, were sampled with a large suction sampler 18, 42, and 85 h (day experiment) and 6, 30, and 78 h (night experiment) after treatment. Rows located 5, 10, 20, and 300 m away from the treated row were similarly sampled. Of seven generalist predators, only one accumulated on the treated rows compared to the untreated rows. Of the other six, five were found in lower numbers on the treated rows, and for one no significant effects were detected. Compared to pre-spray baseline levels, numbers of several taxa increased across the whole field after spraying, suggesting area-wide attraction, but localized responses to the treated rows were weak, and apparent repellence was more common than attraction. We suggest that attract-and-kill with plant volatiles should have minimal effects on populations of these predators, and is likely to be compatible with integrated pest management.

Developing Bisexual Attract-and-Kill for Polyphagous Insects: Ecological Rationale versus Pragmatics

We discuss the principles of bisexual attract-and-kill, in which females as well as males are targeted with an attractant, such as a blend of plant volatiles, combined with a toxicant. While the advantages of this strategy have been apparent for over a century, there are few products available to farmers for inclusion in integrated pest management schemes. We describe the development, registration, and commercialization of one such product, Magnet(®), which was targeted against Helicoverpa armigera and H. punctigera in Australian cotton. We advocate an empirical rather than theoretical approach to selecting and blending plant volatiles for such products, and emphasise the importance of field studies on ecologically realistic scales of time and space. The properties required of insecticide partners also are discussed. We describe the studies that were necessary to provide data for registration of the Magnet(®) product. These included evidence of efficacy, including local and area-wide impacts on the target pest, non-target impacts, and safety for consumers and applicators. In the decade required for commercial development, the target market for Magnet(®) has been greatly reduced by the widespread adoption of transgenic insect-resistant cotton in Australia. We discuss potential applications in resistance management for transgenic cotton, and for other pests in cotton and other crops.

Influence of Two Acyclic Homoterpenes (Tetranorterpenes) on the Foraging Behavior of Anthonomus grandis Boh

Previous studies have shown that the boll weevil, Anthonomus grandis, is attracted to constitutive and conspecific herbivore-induced cotton volatiles, preferring the blend emitted by cotton at the reproductive over the vegetative stage. Moreover, this preference was paralleled by the release of the acyclic homoterpenes (tetranorterpenes) (E)-4,8-dimethyl-1,3,7-nonatriene (DMNT) and (E,E)-4,8,12-trimethyltrideca-1,3,7,11-tetraene (TMTT) in Delta Opal cotton being higher at the vegetative than at the reproductive stage. Here, we evaluated whether this difference in release of acyclic homoterpenes also occurred in other cotton varieties, and if boll weevils could recognize these compounds as indicators of a specific cotton phenological stage. Results showed that cotton genotypes CNPA TB-90, BRS-293 and Delta Opal all produced higher levels of DMNT and TMTT at the vegetative stage than at the reproductive stage and that these homoterpenes allowed for principal component analysis separation of volatiles produced by the two phenological stages. Electroantennograms confirmed boll weevil antennal responses to DMNT and TMTT. Behavioral assays, using Y-tube olfactometers, showed that adding synthetic homoterpenes to reproductive cotton volatiles (mimicking cotton at the vegetative stage in terms of homoterpene levels) resulted in reduced attraction to boll weevils compared to that to unmodified reproductive cotton. Weevils showed no preference when given a choice between plants at the vegetative stage and the vegetative stage-mimicked plant. Altogether, the results show that DMNT and TMTT are used by boll weevils to distinguish between cotton phenological stages.

Interference of plant volatiles on pheromone receptor neurons of male Grapholita molesta (Lepidoptera: Tortricidae)

In moths, sex pheromone components are detected by pheromone-specific olfactory receptor neurons (ph-ORNs) housed in sensilla trichodea in the male antennae. In Grapholita molesta, ph-ORNs are highly sensitive and specific to the individual sex pheromone components, and thus help in the detection and discrimination of the unique conspecific pheromone blend. Plant odors interspersed with a sub-optimal pheromone dose are reported to increase male moth attraction. To determine if the behavioral synergism of pheromone and plant odors starts at the ph-ORN level, single sensillum recordings were performed on Z8-12:Ac and E8-12:Ac ph-ORNs (Z-ORNs and E-ORNs, respectively) stimulated with pheromone-plant volatile mixtures. First, biologically meaningful plant-volatile doses were determined by recording the response of plant-specific ORNs housed in sensilla auricillica and trichodea to several plant odorants. This exploration provided a first glance at plant ORNs in this species. Then, using these plant volatile doses, we found that the spontaneous activity of ph-ORNs was not affected by the stimulation with plant volatiles, but that a binary mixture of sex pheromone and plant odorants resulted in a small (about 15%), dose-independent, but statistically significant, reduction in the spike frequency of Z-ORNs with respect to stimulation with Z8-12:Ac alone. The response of E-ORNs to a combination of E8-12:Ac and plant volatiles was not different from E8-12:Ac alone. We argue that the small inhibition of Z-ORNs caused by physiologically realistic plant volatile doses is probably not fully responsible for the observed behavioral synergism of pheromone and plant odors.

Make love not war: a common arthropod defence compound as sex pheromone in the forest cockchafer Melolontha hippocastani

Mate finding in the forest cockchafer, Melolontha hippocastani, occurs during a spectacular swarming period at dusk. The swarming flights are mainly performed by males whereas most of the females stay within the host trees and continue feeding. Males orientate towards damage-induced green leaf volatiles (GLV) allowing location of mechanically damaged foliage. In order to distinguish between unspecific leaf damage and damage caused by feeding females, male cockchafers orientate by a sex attractant. Here we show this compound to be 1,4-benzoquinone, which has been known for more than 40 years as a highly effective defence compound used by numerous arthropod species to repel enemies. 1,4-benzoquinone synergistically increased the number of males caught in GLV-baited funnel traps during the swarming period. Significantly more males landed on wire cages baited with a combination of 1,4-benzoquinone and GLV than on cages baited with only GLV. The results suggest that the sex pheromone of M. hippocastani might have evolved from a primary role as a defence compound.