Gas Chromatographic-electroantennographic Detection Research Articles

Tritrophic Interactions Mediated by Zoophytophagous Predator-Induced Host Plant Volatiles.

The zoophytophagous mirid predator Nesidiocoris tenuis and the ectoparasitoid Stenomesius japonicus are important biological control agents for several agricultural pests including the invasive leafminer, Phthorimaea absoluta, a destructive pest of Solanaceous crops especially tomato in sub-Saharan Africa. However, little is known about how feeding by N. tenuis can influence the tritrophic interactions in the tomato plant. Here, we tested the hypothesis that N. tenuis phytophagy would influence the tritrophic olfactory interactions between the host plant tomato and pest, predator, and parasitoid. In olfactometer assays, P. absoluta females and N. tenuis adults were both attracted to constitutive volatiles released by the tomato plant. Whereas females of P. absoluta avoided volatiles released by N. tenuis-infested plants, S. japonicus females and N. tenuis adults were attracted to the induced volatiles. In coupled gas chromatography-electroantennographic detection (GC-EAD) recordings of intact and N. tenuis-infested plant volatiles, antennae of P. absoluta and S. japonicus females both detected eight components, whereas N. tenuis adults detected seven components which were identified by GC-mass spectrometry (GC-MS) as terpenes and green leaf volatiles (GLVs). Dose-response olfactometer bioassays revealed that the responses of P. absoluta, N. tenuis, and S. japonicus varied with the composition and concentration of blends and individual compounds tested from N tenuis-induced volatiles. Females of P. absoluta showed no preference for an eight-component blend formulated from the individual repellents including hexanal, (Z)-3-hexenyl butanoate, and δ-elemene identified in the volatiles. On the other hand, S. japonicus females were attracted to an eight-component blend including the attractants (E)-2-hexenal, (Z)-3-hexenol, methyl salicylate, β-phellandrene, and (E)-caryophyllene. Likewise, N. tenuis adults were attracted to a seven-component blend including the attractants β-phellandrene, δ-elemene, and (E)-caryophyllene identified in the volatiles. Our findings suggest that there is potential for the use of terpenes and GLVs to manage the insects in the tritrophic interaction.

Volatile Organic Compounds Mediate Host Selection of Wheat Midge, Sitodiplosis Mosellana (Géhin) (Diptera: Cecidomyiidae) between Preanthesis and Postanthesis Stages of Wheat.

The orange wheat blossom midge, Sitodiplosis mosellana (Géhin) (Diptera: Cecidomyiidae), is a significant wheat pest in the Prairie Provinces of Canada and northern regions of the USA. Wheat phenology plays a critical role in wheat midge oviposition. We hypothesized that S. mosellana oviposition behaviour is influenced by volatile organic compounds (VOCs) emitted by wheat at two adjacent wheat growth stages: preanthesis and postanthesis. A higher number of S. mosellana eggs laid on preanthesis than postanthesis spikes in an oviposition choice experiment using the susceptible spring wheat cultivar 'Roblin'. In preanthesis, wheat emitted higher amounts of Z-3-hexenyl acetate (Z3-06:OAc) than at the postanthesis stage. Higher amounts of methyl ketones such as 2-tridecanone, 2-pentadecanone, and 2-undecanone were emitted by wheat in the postanthesis stage and these VOCs were sensitive to S. mosellana antennae used in the Gas Chromatography-Electroantennographic Detection. Females were attracted to synthetic Z3-06:OAc but were deterred by 2-tridecanone relative to the solvent control in the vertical Y-tube olfactometer. 2-Undecanone and 2-pentadecanone did not show any attractiveness or deterrence. In a no-choice oviposition experiment, fewer eggs were laid in preanthesis wheat exposed to a synthetic VOC blend of Z3-06:OAc, 2-undecanone, 2-tridecanone, and 2-pentadecanone at the concentrations released by postanthesis spikes. This study shows that the reduction of Z3-06:OAc, in the VOC mix, and possibly the increase in 2-tridecanone, are likely responsible for the reduction in oviposition on postanthesis wheat. These results elucidate for the first time the role of specific VOCs mediating S. mosellana oviposition in preanthesis and postanthesis wheat.

Behavioral preferences of Solenopsis invicta Buren to essential oils and active compounds from amiaceae plants

The red imported fire ant (RIFA) (Solenopsis invicta Buren) has caused serious ecological and public safety problems in invasive areas. While extensive use of pesticides to control RIFA may negatively affect human health and environment, essential oils (EOs) of Lamiaceae possessing aromatic smell and multiple biological activities are potential alternatives of chemical pesticides. In this study, we evaluated the behavioral preferences of different castes of RIFA towards the EOs from five species of Lamiaceae plants (Salvia miltiorrhiza, Perilla frutescens, Pogostemon cablin, Schizonepeta tenusfolia, Mentha canadensis), and then investigated the active compounds in these EOs that trigger insect behavioral preferences by gas chromatography-electroantennographic detection (GC-EAD). The results of behavioral experiment indicated that three EOs strongly altered the behavior of RIFA. Notably, all concentrations of P. frutescens EO showed a significant repellent activity on virgin queen ants, with a repellent rate of 62.50% at the lowest concentration of 2 μg/ml. The repellent effect of S. tenusfolia EO against small worker ants reached a very significant difference between control and treatment groups, with the highest repellent rate of 85.00% observed at 1000 μg/ml. Save for the lowest concentration 2 μg/ml, other doses of M. canadensis EO showed a remarkable repellent effect on small worker ants, demonstrating a positive dose-effect relationship (with repellent rates of 77.50% and 65.00% at 1000 and 8 μg/ml, respectively). A total of 39 EAD-active compounds were detected in these EOs, and 12 of them were subsequently evaluated for behavioral preferences of RIFA. Our findings indicated that six compounds (menthone, menthol, caryophyllene oxide, pulegone, 3-methylcyclopentanol, eugenol) consistently triggered behavioral preferences in worker ants. Meanwhile, six compounds, including borneol, eugenol, phenylethyl alcohol, perilla ketone, 3-methylcyclopentanol, α-guaiene, were found to significantly alter the behavioral selectivity of virgin queen ants. These results may help to develop application value of selected Lamiaceae plants EOs and contribute to the exploration of new green control methods for invasive pests.

Direct and indirect host‐related volatile compounds attract a fruit fly parasitoid, Diachasmimorpha longicaudata

AbstractFruit fly pests (Diptera: Tephritidae) are a serious problem for fruit production and for local and international trade. Biological control is increasingly included as a pest control tool within integrated pest management (IPM) programmes, seeking to reduce pesticides and improve fruit quality. Ceratitis capitata Wiedemann, the Mediterranean fruit fly (medfly), is probably the most damaging fruit fly pest, with a global distribution and more than 200 host species. The solitary larval endoparasitoid Diachasmimorpha longicaudata Ashmead (Hymenoptera: Braconidae) is a biocontrol agent widely used against Tephritidae fruit fly pests. Previous studies showed that female wasps locate host larvae using visual, mechanical, and chemical cues. Here, we investigated the chemical basis of female parasitoid attraction to cues that guide D. longicaudata to the host, and thus unveil volatile organic compounds that might be used in IPM programmes. Female orientation to chemical cues was tested in a Y‐tube olfactometer, where attraction to C. capitata‐infested oranges, oranges with residues of larval activity, oranges infected with a green mould, and overripe oranges was confirmed. Volatiles from all these types of fruit were collected and used in gas chromatography‐electroantennographic detection (GC‐EAD) and GC‐mass spectrometry (MS) analyses. These studies allowed us to identify six candidate compounds that were present in all treated oranges but not in the control fruit (ripe and uninfested oranges): D‐limonene, acetophenone, linalool, nonanal, decanal, and eugenol. Electroantennography (EAG) showed that acetophenone, nonanal, and decanal triggered dose‐dependent responses, suggesting a relevant role in the process of host finding. Although responses to D‐limonene, linalool, and eugenol were independent of the dose, they could be involved in host location in areas with high probability of host presence. The fact that these six compounds are shared by the four behaviourally attractive sources opens new possibilities for the development of novel tools to improve biocontrol programmes.

Structure, Synthesis, and Bioassays of Sex Pheromone for Pyrausta machaeralis (Lepidoptera: Crambidae).

The leaf skeletonizer, Pyrausta machaeralis (Lepidoptera: Crambidae), is a serious insect pest of teak (Tectona grandis) in China. The application of insect pheromones is widely applied as an environmentally friendly technology for integrated pest management (IPM). In the present study, crude extracts of sex pheromone glands of calling P. machaeralis females were collected and then analyzed using gas chromatography/electroantennographic detection (GC/EAD) and gas chromatography-mass spectrometry (GC-MS). The combination of infrared spectroscopy (IR) and nuclear magnetic resonance (NMR) spectrometry was used for structure identification. Afterward, their electrophysiological and behavioral activity was evaluated in the laboratory and field. Herein, we eventually determined two active components, E-11-tetradecenyl acetate (E11-14:Ac) and Z-11-tetradecenyl acetate (Z11-14:Ac), at a ratio of 96:4, as the sex pheromone of P. machaeralis. The identification of sex pheromones would facilitate the development of efficient strategies for monitoring and controlling the field populations of P. machaeralis.

Behavioral responses of potato tuber moth (Phthorimaea operculella) to volatiles from wilted Yunnan poplar (Populus yunnanensis)

AbstractThe volatiles from wilted poplar leaves possess a broad spectrum of attractants that affect various lepidopteran pests. The effect of volatile compounds of wilted leaves of Yunnan poplar, Populus yunnanensis Dode (Salicaceae), on the orientation and oviposition behavior of the potato tuber moth (PTM), Phthorimaea operculella Zeller (Lepidoptera: Gelechiidae), has not been well understood. In this study we identified 15 active compounds from the wilted Yunnan poplar leaves to gravid female PTM by combined gas chromatography‐electroantennographic detector (GC‐EAD) and gas chromatography–mass spectrometry (GC–MS) in this study. We evaluated the biological activity of these compounds at their natural level with a Y‐tube olfactometer and self‐made oviposition cages. The results showed that six compounds – cis‐3‐hexen‐1‐ol, 6‐methyl‐5‐hepten‐2‐one, hexyl acetate, 2‐hydroxybenzaldehyde, trans‐ocimene, and 2‐pentylfuran – exhibited significant attraction to gravid female PTM, and five compounds – trans‐2‐nonenal, styrene, hexyl formate, trans‐ocimene, and 2‐pentylfuran – attracted them to lay eggs, both individually and in blend. Apart from styrene, all these compounds may serve as attractants for attract‐and‐kill to PTM.

N-octyl acrylate is a candidate sex pheromone component involved in courtship in parasitoid wasp Microplitis mediator.

Sex pheromones are considered to play critical roles in partner communication of most parasitic Hymenoptera. However, the identification of sex pheromone components remains limited to a few families of parasitoid wasps. In this study, we functionally characterized a candidate sex pheromone component in Microplitis mediator (Hymenoptera: Braconidae), a solitary parasitoid of Noctuidae insects. We found that the body surface extract from female wasps could significantly stimulate courtship behavior of males. Gas chromatography-electroantennographic detection (GC-EAD) analysis revealed that a candidate semiochemical from extract triggered significant electrophysiological response of antennae of males. By performing gas chromatography-mass spectrometer (GC-MS) measurement, GC-EAD active compound was identified as n-octyl acrylate, a candidate sex pheromone component in female M. mediator. In electroantennogram (EAG) tests, antennae of male wasps showed significantly higher electrophysiological responses to n-octyl acrylate than those of females. Y-tube olfactometer assays indicated that male wasps significantly chose n-octyl acrylate compared with the control. Furthermore, male wasps showed a remarkable preference for n-octyl acrylate in a simulated field condition behavioral trial; simultaneously, n-octyl acrylate standard could also trigger significant courtship behavior in males. We propose that n-octyl acrylate, as a candidate vital sex pheromone component, could be utilized to design behavioral regulators of M. mediator to implement the protection and utilization of natural enemies.

A supergene in seaweed flies modulates male traits and female perception.

Supergenes, tightly linked sets of alleles, offer some of the most spectacular examples of polymorphism persisting under long-term balancing selection. However, we still do not understand their evolution and persistence, especially in the face of accumulation of deleterious elements. Here, we show that an overdominant supergene in seaweed flies, Coelopa frigida, modulates male traits, potentially facilitating disassortative mating and promoting intraspecific polymorphism. Across two continents, the Cf-Inv(1) supergene strongly affected the composition of male cuticular hydrocarbons (CHCs) but only weakly affected CHC composition in females. Using gas chromatography-electroantennographic detection, we show that females can sense male CHCs and that there may be differential perception between genotypes. Combining our phenotypic results with RNA-seq data, we show that candidate genes for CHC biosynthesis primarily show differential expression for Cf-Inv(1) in males but not females. Conversely, candidate genes for odorant detection were differentially expressed in both sexes but showed high levels of divergence between supergene haplotypes. We suggest that the reduced recombination between supergene haplotypes may have led to rapid divergence in mate preferences as well as increasing linkage between male traits, and overdominant loci. Together this probably helped to maintain the polymorphism despite deleterious effects in homozygotes.

Identification and evaluation of cruciferous plant volatiles attractive to Plutella xylostella L. (Lepidoptera: Plutellidae).

The diamondback moth, Plutella xylostella, has developed resistance to almost all insecticides used for its control. The 'push-pull' method has been shown as an effective control strategy to address this resistance challenge of P. xylostella. The key focus of the strategy is the identification of attractive or repellent volatile components. The aim of this study was to identify attractive volatile compounds released from host plants. Identified compounds were applied in the biological control of this pest. Nine active compounds released into the headspace of seven cruciferous plant species were identified using gas chromatography-electroantennographic detection and gas chromatography-mass spectrometry. Electroantennographic detection-active compounds included five green leaf volatiles (hexanal, trans-2-hexen-1-ol, cis-3-hexen-1-ol, cis-3-hexenyl acetate, and 1-penten-3-ol), three isothiocyanates (isopropyl isothiocyanate, allyl isothiocyanate, and butyl isothiocyanate), and nonanal. Except for nonanal, all the identified green leaf volatiles and isothiocyanates elicited strong electrophysiological and behavioral responses in P. xylostella. The strongest attractive compounds, trans-2-hexen-1-ol and isopropyl isothiocyanate, were further evaluated in oviposition and field-trapping assays. Results showed that they both lured female moths to lay eggs, and were highly attractive to P. xylostella adults in field, especially when used in combination with yellow and green sticky boards. However, a blend of the two compounds showed no synergistic effect, but rather an antagonistic effect. Green leaf volatiles and isothiocyanates were identified as key olfactory cues for host selection of P. xylostella. Trans-2- hexen-1-ol and isopropyl isothiocyanate were identified as candidate attractive compounds to serve in a 'push-pull' strategy for P. xylostella control. © 2023 Society of Chemical Industry.

Herbivore intraguild interactions decrease ectoparasitoid Bracon nigricans parasitism of Phthorimaea absoluta and responses to tomato volatiles

Intraguild interactions are known to trigger competition among phytophagous insects that depend on the same food source, which may have implications on natural enemy performance. Here, we tested the hypothesis that intraguild interactions between the greenhouse whitefly, Trialeurodes vaporariorum, and the South American tomato pinworm, Phthorimaea absoluta on the host plant tomato would affect performance of the pinworm ectoparasitoid Bracon nigricans. In oviposition bioassays, P. absoluta females significantly laid more eggs and were attracted to tomato plants infested with T. vaporariorum than uninfested plants. Additionally, T. vaporariorum infestation decreased B. nigricans parasitism on P. absoluta larvae and attraction to tomato plants. In coupled gas chromatography-electroantennographic detection (GC-EAD) recordings, antennae of P. absoluta and B. nigricans females detected 18 and 15 components, respectively from the herbivore-induced volatiles, which were identified by GC-mass spectrometry (GC-MS) as green leaf volatiles (GLVs) and terpenes. In dose-response behavioral assays, P. absoluta and B. nigricans responses varied with the composition and concentration of blends and individual compounds tested. Whereas P. absoluta was attracted to GLVs and terpenes, B. nigricans avoided most of these chemicals, especially the GLV (E)-2-hexenal and terpenes δ-3-carene, and (E)-caryophyllene. The results suggest that herbivore intraguild interactions can influence the behavioral ecology and performance of natural enemies which may have evolutionary significance. Also, these specific GLVs and terpenes can be exploited in the management of P. absoluta.

Electroantennogram and behavioural responses of Plutella xylostella to volatiles from the non‐host plant Mentha spicata

AbstractPlutella xylostella Linnaeus (Lepidoptera: Plutellidae) is one of the most important pests of cruciferous vegetables. Mechanically damaged Mentha spicata Linnaeus (Lamiales: Lamiaceae) strongly repels P. xylostella adults; however, the repellent mechanism remains unclear. In this study, the repellent mechanism was explored based on the electroantennogram (EAG) and behavioural responses of P. xylostella to volatiles from the damaged M. spicata. First, the active volatile compounds in the headspace volatiles of damaged M. spicata were identified by gas chromatography‐electroantennographic detection (GC‐EAD) and gas chromatography–mass spectrometry (GC–MS). Furthermore, the EAG and behavioural responses of P. xylostella to these compounds were investigated. The GC‐EAD results indicated that four compounds, 2,4‐dimethylheptane, 4‐methyloctane, 2‐methylnonane, and myrcene induced EAG responses in female antennae. 2‐methylnonane and myrcene elicited strong dose‐dependent EAG responses starting at a dose of 1 μg/μL. Choice tests in a four‐arm olfactometer showed significant repellent effects of the four compounds on P. xylostella adults at 100 μg/μL, and the repellent indices of 2,4‐dimethylheptane, 4‐methyloctane, 2‐methylnonane, and myrcene were 70.0%, 76.7%, 66.7%, and 73.3% to mated females, respectively. Finally, oviposition repellence assays showed that female adults were significantly repelled by these compounds, and the oviposition repellent index for myrcene was 23.9%. 2,4‐dimethylheptane, 4‐methyloctane, 2‐methylnonane, and myrcene mediate the repellence of wounded M. spicata to P. xylostella adults, suggesting that the four compounds contribute towards developing behavioural regulators of this important pest.

The attractive host volatiles can enhance oviposition of Anoplophora glabripennis on a non-host tree.

The Asian longhorned beetle (ALB), Anoplophora glabripennis, is a serious wood borer of hardwood trees. Populus deltoides 'Shalinyang' (PdS) is attractive to ALB adults for oviposition but highly resistant to their offspring. Investigation of the chemicals regulating ALB oviposition is scarce in previous studies until now. To determine which chemicals emitted by PdS were attractive and induced oviposition behavior by ALB on non-host poplar tree species, we first: collected and identified the bio-active volatiles produced by PdS using coupled gas chromatography-mass spectrometry (GC-MS) and coupled gas chromatography-electroantennographic detector (GC-EAD); then evaluated which chemicals were attractive in a Y-tube olfactometer bioassay; and finally screened key compounds affecting ALB oviposition using a 'chemical-stimulated oviposition on non-host tree' bioassay. (E)-2-Hexenal, hexyl acetate, (Z)-3-hexenol acetate, 1-hexanol, (Z)-3-hexenol, β-caryophyllene, and salicylaldehyde emitted from PdS were attractive to ALB. When (E)-2-hexenal, 1-hexanol, (Z)-3-hexenol acetate, and (Z)-3-hexenol were applied to the non-host tree Populus tomentosa, oviposition by ALB females was significantly increased. Furthermore, the mean number of oviposition pits increased as the (Z)-3-hexenol concentrations increased. Further tests on synergy between pairs of chemicals showed that (Z)-3-hexenol stimulated production of the most oviposition pits, but that the percentage of effective oviposition pits (those containing an egg and larva and not empty) decreased. (Z)-3-Hexenol is the main chemical component inducing ALB oviposition. These results increase understanding about the oviposition behavior of ALB and could help improve management strategies that regulate ALB behavior by planting mixed-species forests resistant to ALB. © 2023 Society of Chemical Industry.

Behavioural and Electrophysiological Response of <i>Trichogramma achaea</i> to Oviposition Induced Volatiles in Tomato

A laboratory experiment was conducted at ICAR-National Bureau of Agricultural Insect Resources, Bengaluru to study the behavioural response of Trichogramma achaea towards healthy, conspecifics (Tuta absoluta oviposited on Tuta absoluta infested plants) and heterospecifics (Tuta absoluta oviposited on Liriomyza trifolii infested plants) tomato plants by choice and no-choice parasitization assays and olfactometer studies. Headspace volatiles were collected from tomato plants oviposited by conspecifics, heterospecifics and healthy plants, analysed using gas chromatography-mass spectrometry (GC-MS) where 14, 17 and 8 volatile organic compounds were detected respectively. Electrophysiological compounds and antennal response of T. achaea were identified using gas chromatography-electro-antennographic detector (GC-EAD). EAD active compounds of T. achaea were 3-Hexanol, α-phellandrene, trans-β- ocimene, pentacosane and γ-terpinene.

Herbivore induced fruit volatiles guide the solitary tephritid endoparasitoid Diachasmimorpha longicaudata (Hymenoptera: Braconidae) in selecting an oviposition substrate.

Oviposition in a generalist parasitoid is a complex process that involves interactions among its host, host plant, and spatiotemporal environment. Our study was aimed at exploring the ability of a generalist parasitic wasp, Diachasmimorpha longicaudata (Ashmead) (Hymenoptera: Braconidae), in perceiving odor cues from its host insect [Oriental fruit fly Bactrocera dorsalis (Hendel, Diptera: Tephritidae)] in infested mango fruits. A series of experiments involving behavioral and electrophysiological studies suggest that D. longicaudata is able to distinguish host infested fruit volatiles from uninfested. Additionally, we found that D. longicaudata can distinguish between high and low-level infestations using specific cues emanating from fruits. Coupled gas chromatography-electroantennographic detection (GC-EAD) and gas chromatography-mass spectrometry (GC-MS) analysis of infested mango fruit head space volatiles identified compounds such as ethyl butanoate, ethyl 3-hydroxybutyrate, β-myrcene, trans-β-ocimene, allo-ocimene, ethyl octanoate, ethyl-α-toulate, β-elemene, β-caryophyllene, humulene, caryophyllene oxide, ethyl dodecanoate, ethyl hexadecanoate, 2-furancarboxylic acid, 3-hydroxy-2-methyl-4-pyrone, and phenethyl alcohol emanated from three different host treatments with different levels of larval infestation which elicited antennal responses in D. longicaudata. We suggest that these cues might play a significant role in attracting D. longicaudata in the field.

Pine Emperor moths from KwaZulu-Natal use the same pheromone component previously isolated from Nudaurelia cytherea (Lepidoptera: Saturniidae) from the Western Cape

Nudaurelia spp. (Saturniidae) are sporadic pests of pine plantations in South Africa. Taxonomic uncertainty exists in South Africa with this group and represents an impediment to the development and implementation of pheromone-based management tactics. Populations from the Western Cape have been described as Nudaurelia cytherea while those from KwaZulu-Natal and Mpumalanga have been described as Nudaurelia clarki. We compared Cytochrome oxidase subunit I (COI) gene sequences from moths from the Western Cape, KwaZulu-Natal (KZN) and Mpumalanga regions. We also analysed female pheromone gland extracts with gas-chromatography electroantennographic detection (GC-EAD) and gas-chromatography-mass spectrometry (GC-MS) for moths from KwaZulu-Natal and Mpumalanga. COI gene barcoding sequences were identical for moths from the Western Cape, KwaZulu-Natal (KZN) and Mpumalanga regions providing preliminary evidence to suggest that these populations may be the same species. Based on the available literature, the morphology and origin of our samples suggests that pheromone analyses in this study were done on N. clarki. Male N. clarki antennae respond to two compounds in female extracts. One of these compounds was confirmed with a synthetic standard to be (Z)-dec-5-en-1-yl-3-methylbutanoate, the sex pheromone previously identified from N. cytherea. The identity of the second compound could not be confirmed. Both male and female antennae responded to four structurally related compounds in the synthetic pheromone standard. Field trials with custom-made traps confirmed attraction of N. clarki males to polydimethylsiloxane and polyisoprene lures loaded with synthetic (Z)-dec-5-en-1-yl-3-methylbutanoate.

Olfactory Stimulants for Sirex nigricornis (Hymenoptera: Siricidae) and its Parasitoid, Ibalia leucospoides (Hymenoptera: Ibaliidae), in Odors of Stressed and Bark Beetle–Colonized Pines

Abstract We conducted studies with the native woodwasp Sirex nigricornis F. (Hymenoptera: Siricidae) in Louisiana to identify host-associated olfactory stimulants that may include attractive semiochemicals for this species as well as Sirex noctilio F., an invasive species that can attack healthy trees. Loblolly pines (Pinus taeda L.) treated with a stressing agent were felled and chipped 1–2 mo after treatment, and the chips were steam–water distilled in a Clevenger apparatus to extract volatile compounds. Using coupled gas chromatography–electroantennographic detection, we analyzed the distillates with antennae of both S. nigricornis and the Sirex parasitoid Ibalia leucospoides (Hochenwarth) (Hymenoptera: Ibaliidae) to identify olfactory stimulants. In addition, we assayed S. nigricornis antennae with synthetic mixtures containing 23 volatile compounds associated with stressed and dying pines, including pheromones of bark beetles (Coleoptera: Curculionidae: Scolytinae) that also use these hosts. Antennae of both male and female S. nigricornis responded to 29 identifiable volatiles in the distillates, whereas I. leucospoides responded to 23 volatiles. Eighteen compounds in the synthetic mixtures were olfactory stimulants for S. nigricornis. Olfactory stimulants in the woodchip distillates were predominantly hydrocarbon and oxygenated monoterpenes, and the strongest antennal stimulants among compounds in the synthetic mixtures were oxygenated monoterpenes associated with pine death and early decay (e.g., verbenone, fenchone, and terpinen-4-ol). Bark beetle pheromones (frontalin, endo-brevicomin, ipsenol, and ipsdienol) also stimulated S. nigricornis antennae. The very large number of host-associated olfactory stimulants for S. nigricornis implies that our data may offer limited assistance in targeting individual compounds for investigation as possible attractants and components for a Sirex lure.

Development of a pheromone monitoring system for the goosefoot groundling moth, Scrobipalpa atriplicella (von Röslerstamm) in quinoa, Chenopodium quinoa (Willdenow)

The goosefoot groundling moth, Scrobipalpa atriplicella, (Lepidoptera: Gelechiidae) is a serious pest of quinoa, Chenopodium quinoa, in North America and Europe. Previous studies found male S. atriplicella were attracted to a generic pheromone lure containing (Z)-5-dodecenyl acetate. Here, we identified further candidate sex pheromone components from female pheromone glands using gas chromatography-electroantennographic detection. We confirmed (Z)-5-dodecenyl acetate to be an antennally active compound, and identified a previously unidentified minor component, (E)-5-dodecenyl acetate. Field tests confirmed males were most attracted to a two-component blend in a 95:5 ratio of (Z)-5-dodecenyl acetate to (E)-5-dodecenyl acetate. We found that the 95:5 major to minor ratio captured more S. atriplicella moths and the lowest number of non-target noctuid moths compared to other ratios tested. The number of S. atriplicella captured varied with trap type, but not the two heights tested (0.5 and 1 m), however, we recommend pheromone-baited wing traps deployed at either at 0.5 or 1 m heights to reduce the possibility of trap saturation with sticky traps with smaller surface areas. These findings allow for future development of a pheromone-based monitoring program for this significant pest of quinoa in Canada.

GC-MS/FID/EAD: A method for combining mass spectrometry with gas chromatography-electroantennographic detection

Gas chromatography-electroantennographic detection (GC-EAD), typically combined with a flame ionization detector (FID), is a widely used technique for studying insect semiochemicals. Combining mass spectrometry (MS) with GC-EAD is extremely beneficial, but has seldom been adopted, possibly due to the practical challenges associated with incorporating an MS (under vacuum) into a GC-EAD system. We describe a novel method of incorporating MS into a GC-EAD system, where the FID is maintained in the system rather than being replaced by an MS. With this method, effluent is still split between EAD and FID, with the FID being used to assign components that elicit antennal responses, as in a normal GC-FID/EAD system. The MS is introduced via a second effluent splitter inserted before the split between the EAD and the FID. This method allows for EAD, FID, and MS data to be obtained from a single injection, which is especially useful for analysis of thermally desorbed and solid-phase microextraction (SPME) samples. This configuration is also relatively simple to implement and resolves some of the practical challenges associated with dividing effluent between a detector at atmospheric pressure (a live antenna) and a detector under vacuum (the MS). We present test runs with hawkmoth antennae and floral volatiles to demonstrate the effectiveness of this system, and discuss the challenges and practical solutions to incorporating MS into a GC-EAD system that retains an FID detector.

Volatiles from Eucalyptus Trunks and Forest Floor Humus Influence the Habitat Transfer, Host Selection, and Aggregation of Endoclita signifer Larvae

Endoclita signifer is a major wood-boring pest of eucalyptus trees in China, and its third instar larvae can accurately find and infest eucalyptus trees in mixed-species forests, although it can also feed on another 51 tree species in the same planted area. A total of 34 volatile compounds were identified from eucalyptus trunks, including non-infested and infested trunks with single or multiple (more than three) larval entrance cover packets, and forest floor humus. Of these, o-cymene showed a strong gas chromatography-electroantennographic detection (GC-EAD) activity and significant attraction of the third instar E. signifer larvae. Higher abundance of alpha-phellandrene, o-cymene, and the unique 2-phenyl-2-propanol in the volatile profile from infested eucalyptus trunks indicated that they were herbivore-induced plant volatiles (HIPVs). The larvae showed significantly higher attraction to volatile blends, especially those from infested eucalyptus trunks, than to single volatiles. A blend of the three HIPVs, α-pinene, D-limonene, and n-butyl ether may serve as an attractant for the control of E. signifer larvae in eucalyptus plantations. Further, exposure of third instar E. signifer larvae to some of these volatiles which also elicited electroantennogram and behavioral responses, influenced expressions of some olfactory proteins. Our results show that third instar E. signifer larvae can recognize o-cymene from host eucalyptus trunks and are attracted to the trunk by the three HIPVs when they shift their habitats from the forest floor humus to the tree trunks.

Study of behavioral, electrophysiological response, and the active compounds of the essential oils from six kinds of flowers against Solenopsis invicta Buren (Hymenoptera: Formicidae)

Red imported fire ant (RIFA), Solenopsis invicta Buren, which is an invasive alien ant, causes serious ecological and public safety problems. Concerns about the impact of traditional synthetic pesticides on nontarget organisms, plant essential oils (EOs) as alternative products with lower environmental impact can be used to control insects. The "push-pull" strategy is considered to be a method of controlling the number and distribution of pests through attraction and repulsion. To find active compounds with effect on the behavior of RIFA, 6 types of EO of plant flowers with a strong aroma, including Osmanthus fragrans (Thunb.) Lour., Sophora japonica Linn, Eugenia caryophμllata Thunb., Ligustrum compactum (Wall. exG. Don) Hook.f., Jasminum sambac (L.) Ait., Allium polyrhizum Turcz. Ex Regel were studied by Y-tube experiment, electrophysiological detection (EAG), and gas chromatography-electroantennographic detection (GC-EAD). The results showed that different concentrations of six EOs significantly affected the behavioral selectivity of different castes of RIFA, the data of high concentration-repellent and low concentration-attractive have been recorded. The repellent rate of 1000 μg/ml L. compactum of EO was 68.75 % and the attraction rate of 2 μg/ml of EO was 66.25 % on small worker ants. For large worker ants, both 1000 μg/ml (repellent rate: 72.50 %) and 40 μg/ml (attractive rate: 68.75 %) of L. compactum EO reached an extremely significant difference. As for E. caryophμllata EOs, the repellent rate of male ants was 67.5 % at 1000 μg/ml and 68.75 % of the attraction rate was calculated at 2 μg/ml. The most interesting finding was that all concentrations of L. compactum EOs showed a remarkable attractive effect on virgin ants and the attraction rate of 1000 μg/ml EO reached an extremely significant difference (attraction rate: 72.5 %). The highest absolute EAG values of different castes of RIFA in the EO were followed as: small worker ants (1.8788 mV, J. sambac ), large worker ants (1.5550 mV, O. fragrans ), male ants (1.6088 mV, A. polyrhizum ), and virgin ants (1.2350 mV, E. caryophμllata ). The GC-MS results of the EOs were followed as: the compounds with high content in O. fragrans EO were butyl phthalate (37.95 %) and p -methoxyphenethyl alcohol (16.76 %); the main chemical components in S. japonica EO were benzeneethanol (20.62 %) and phenol (11.16 %); the total contents of eugenol (82.5 %) and aceteugenol (15.81 %) reached 98.31 % in E. caryophμllata EO; the most compound of EO was benzyl alcohol (19.33 %), followed by linalool (18.70 %) in J. sambac EO; the main chemical components of L. compactum EO were benzyl alcohol (17.45 %) and phenethyl alcohol (27.63 %); five compounds, including pentacosane (11.78 %), heptacosane (10.37 %), oleylamide (11.9 %), non-acosane (20.15 %), and octacosane (8.24 %) were the main chemical components in A. polyrhizum EO. The GC-EAD results showed that three compounds (estragole, α -humulene, and caffeine) were identified to have the potential to develop as behavioral orienting chemicals against worker ants of RIFA. Furthermore, several compounds were expected to be developed as attractants for reproductive ants, including eugenol, cis -linalool oxide, furfural, and its analogs. Our data will provide basic materials for the "push-pull" strategy and have the potential to lay the foundation for the eventual development of efficient and safe repellents. • Six kinds of plants flowers essential oils (EOs) with strong special aroma were extracted by steam distillation method. • Different castes of red imported fire ant (RIFA) revealed repellent or attractive activities to the EOs. • The results of electrophysiological (EAG) recordings showed that the EOs triggered the EAG response to different castes of RIFA. • The results of gas chromatography-electroantennographic detection (GC-EAD) showed that 6 compounds have the potential to be developed as behavioral orient chemicals against RIFA.