Electrophysiological and behavioural identification of host kairomones as olfactory cues for Culicoides impunctatus and C. nubeculosus

Electroantennograms (EAGs) were recorded from wild‐caught parous, female Culicoides impunctatus (Goetghebuer) in response to components of host odour. Nine synthetic compounds were found to be electrophysiologically active, eliciting EAGs which were significantly different from solvent control. An EAG hierarchy was established, in which 1‐octen‐3‐ol elicited the highest amplitude EAGs, followed by acetone, lactic acid and butanone. The overall responses to phenolic compounds were reduced compared to the non‐phenolics. Subsequent behavioural analyses of the effects of these compounds when tested singly revealed 1‐octen‐3‐ol, acetone and butanone to be attractive over specific stimulus doses. Exposure to supra‐optimal doses modified the insects’ behaviour; insects either ceased to respond or were repelled. Lactic acid was attractive at the lowest dose tested but was repellent at high doses. Behavioural responses to the phenolic components of host odour and lactic acid were similar, generally causing arrestment at low doses and repelling at the higher doses tested. A comparison of EAG profiles and behavioural assays between laboratory‐reared Culicoides nubeculosus (Meigen) and C. impunctatus suggested that the same kairomones are utilized by both species, with C. nubeculosus being less sensitive than C. impunctatus. The EAG hierarchy of C. nubeculosus to the four non‐phenolics was identical to that of C. impunctatus.     

Antagonist effects of non-host fruit volatiles on discrimination of host fruit by Rhagoletis flies infesting apple (Malus pumila), hawthorn (Crataegus spp.), and flowering dogwood (Cornus florida)

In previous flight‐tunnel tests Rhagoletis pomonella (Walsh) (Diptera: Tephritidae) flies originating from domestic apple (Malus pumila), hawthorn (Crataegus spp.), and flowering dogwood (Cornus florida), displayed greater numbers of upwind flights to blends of volatiles identified from their natal fruit compared to non‐natal fruit. Here, we show that when certain non‐host volatiles were added to the host blend, significantly fewer apple, hawthorn, and dogwood flies exhibited sustained upwind flight to the source. Specifically, the upwind flight of apple flies to the apple blend was significantly antagonized by the addition of the hawthorn or dogwood blends, the addition of 3‐methylbutan‐1‐ol alone (a key volatile for hawthorn and dogwood flies), or the combination of 3‐methylbutan‐1‐ol and another key dogwood volatile, 1‐octen‐3‐ol. Similarly, the upwind flight of dogwood and hawthorn flies to their respective natal blends was antagonized by the addition of the apple blend or the key apple volatile butyl hexanoate. Experiments were also conducted to determine whether non‐natal fruit volatiles could disrupt the close‐range flight response of flies to the visual stimulus of fruit alone, represented by an odorless red sphere. Tests with apple‐origin flies showed that when the hawthorn blend, the dogwood blend, or the key antagonist volatiles from each (3‐methylbutan‐1‐ol and 1‐octen‐3‐ol) were added to a red sphere fruit mimic, significantly lower proportions of flies were captured, compared with captures when no odor was present. Our results support the hypothesis that agonist and antagonist properties of fruit volatiles can play an important role in host recognition/discrimination by Rhagoletis flies.     

Electrophysiological responses of Batocera horsfieldi (Hope) adults to plant volatiles

The olfactory stimuli from the maturation feeding‐plant, Rosa multiflora Thunb., and larval‐host plant, Populus deltoides, of the longhorned beetle, Batocera horsfieldi (Hope), were investigated by using TCT‐GC/MS (Thermal desorption and cold trap, and GC/MS) and electroantennogram recordings (EAG). A total of 20 plant compounds were identified from plant headspace volatile, including aliphatic, aromatic and terpenoid compounds. Five compounds were common to both plants. Eight compounds eliciting strong EAG response were E‐3‐hexenyl acetate, 3‐carene, 1‐penten‐3‐ol, 3‐pentanol, Z‐2‐penten‐1‐ol, hexanal and E‐2‐hexenal. Female and male B. horsfieldi exhibited broad overlap in their EAG responses to individual plant odour, and there was no clear pattern of difference between responses of female and male antennae to different compounds. Mating status had little effect on the EAG responses of females.     

Volatiles released from foliar extract of host plant enhance landing rates of gravid Polygonia c‐album females,but do not stimulate oviposition

The role of olfactory cues for host search is much less investigated in day‐active butterflies than in their relatives, the nocturnal moths. The goal of this study was to investigate whether host‐plant volatiles from foliar extracts of hop, Humulus lupulus L. (Cannabaceae), evoke electroantennographic (EAG) responses, increase landing rates, and stimulate egg‐laying behavior of gravid Polygonia c‐album L. (Lepidoptera: Nymphalidae) females. Eighty‐nine volatile compounds were detected in a non‐concentrated methanol extract of hop by gas chromatography–mass spectrometry, 11 of which elicited an EAG response. Concentration of the crude extract significantly reduced landing rates on artificial leaves treated with the sample due to loss of volatile compounds, but after landing the oviposition response of gravid females was not affected. A mixture of eight commercially available EAG‐active volatiles increased the landing rate of gravid females to their source but did not act as oviposition stimulants. Dividing the volatile compounds into two groups – consisting of (1) hexanal, (E)‐2‐hexenal, octanal, nonanal, and decanal, and (2) sulcatone, humulene, and benzyl alcohol – obliterated effectiveness, revealing synergism between compounds. Although volatiles did not stimulate oviposition, they significantly contributed to the distribution of eggs by increasing the landing rates on treated artificial leaves.     

Electroantennogram responses of a parasitic wasp, Microplitis croceipes, to host-related volatile and anthropogenic compounds

The parasitic wasp Microplitis croceipes (Cresson) (Hymenoptera: Braconidae) showed its own characteristic electroantennogram (EAG) response profiles to 13 host‐related (cis‐3‐hexenol, α‐pinene (R)‐(+)‐limonene (S)‐(–)‐limonene, trans‐β‐ocimene (±)‐linalool, (–)‐trans‐caryophyllene, α‐humulene, nerolidol, trans‐nerolidol, cis‐nerolidol, methyl jasmonate and indole) and four anthropogenic (2‐diisopropylaminoethanol, 2,2′‐thiodiethanol, 2‐methyl‐5‐nitroaniline and cyclohexanone) volatile compounds. These profiles were similar between males and females except for 2‐diisopropylaminoethanol, which elicited significantly larger EAG responses in males. Among the compounds tested, cis‐3‐hexenol, linalool and cyclohexanone elicited the largest EAG responses. EAG responses were not influenced by the age of wasps between 1 and 13 days after emergence. EAG responses were dose‐dependent, and highly EAG‐active compounds elicited significant EAG responses with less than 10 μg of the compounds at source. Quantification of compounds released from an odour cartridge indicates that release rate is highly dependent on the chemical nature of stimuli, showing up to 10 000‐fold differences in the amount released between different compounds when the same amount was loaded in the odour cartridge. Wasps having undergone a behavioural training regime to be attracted to either cyclohexanone or methyl jasmonate did not show any differences in EAG responses from those of untrained wasps.     

Identification of host‐plant chemical stimuli for the European grape berry moth Eupoecilia ambiguella

Olfaction is of major importance for survival and reproduction in moths. Males possess highly specific and sensitive olfactory receptor neurones to detect female sex pheromones. However, the capacity of male moths to respond to host‐plant volatiles is relatively neglected and the role that such responses could play in the sensory ecology of moths is still not fully understood. The present study aims to identify host‐plant stimuli for the European grape berry moth Eupoecilia ambiguella Hb. (Tortricidae, Lepidoptera), a major pest of vine in Europe. Headspace volatiles from Vitis vinifera L. cv. Pinot Noir, Vitis vinifera subsp. sylvestris and five other host‐plant species comprising five different families are analyzed by gas chromatography linked to electroantennogram (EAG) recording from male E. ambiguella antennae and by gas chromatography‐mass spectrometry. This procedure identifies 32 EAG‐active compounds, among them the aliphatic compounds 1‐hexanol, (Z)‐3‐hexenol, (Z)‐3‐hexenyl acetate and 1‐octen‐3‐ol; the terpenes limonene, β‐caryophyllene and (E)‐4,8‐dimethyl‐1,3,7‐nonatriene; and the aromatic compounds benzaldehyde and methyl salicylate. Male and female E. ambiguella show similar EAG response amplitudes to individual chemical stimuli and also to mixtures of plant volatiles, as represented by essential oils from ten other plant species. This possibly indicates a common role for plant compounds in the sensory ecology of the two sexes of E. ambiguella.     

Olfactory antennal responses of the vine weevil Otiorhynchus sulcatus to plant volatiles

Electroantennograms (EAGs) were recorded from the vine weevil, Otiorhynchus sulcatus F. (Coleoptera: Curculionidae) to a broad range of volatile plant compounds. The response profile is restricted to a small number of volatiles that evoke substantial EAGs. Large EAG responses were particularly found among green leaf volatiles (GLV) such as (E)-2-hexenol-1, (Z)-3-hexenol-1, hexanol-1, hexanal, and heptanal. Other plant volatiles eliciting responses in the weevils' antenna are 2,5-dimethylpyrazine, hexylamine, benzylalcohol, 1,2-dimethoxybenzene, o-cresol, myrtenol, 3-methylcyclohexanol, -hexalactone, and -heptalactone. EAG responses to terpenes were generally weak. Many of the monoterpenes are characteristic for the odour of conifers, a group of plants which tend to be avoided by adult vine weevils. The EAG response to several GLV and benzene derivatives in three geographically distinct populations of the vine weevil differed, suggesting between-population variation in receptor sensitivities for several compounds under test. The GLV-composition of the odour profile of potential food plants may be an important criterion for a polyphagous insect like the vine weevil to be used in host-plant selection, since compounds in this odour group dominate so strongly the EAG response profile. In multiple food-choice situations the weevils are known to prefer certain plant species and we hypothesize that they combine GLV information with that of more specific plant volatiles, thereby promoting attraction or avoidance.     

Effects of plant volatiles on electrophysiological and behavioral responses of Cryptorrhynchus lapathi

Electroantennogram (EAG), Y‐tube olfactometer, and wind tunnel bioassays were conducted to test the electrophysiological and behavioral responses of Cryptorrhynchus lapathi L. (Coleoptera: Curculionidae) to six individual volatiles and seven essential oils (compounded volatiles). The aim of this study was to select effective plant compounds that can be used in the development of semiochemical‐based push–pull methods for the control of this harmful insect. Male and female C. lapathi displayed strong EAG responses to linoleic acid, α‐pinene, (Z)‐3‐hexen‐1‐ol, geraniol, turpentine oil, and salicylaldehyde. Y‐tube olfactometer assays indicated that salicylaldehyde and α‐pinene elicited strong repellent effects on female C. lapathi. Linoleic acid and (Z)‐3‐hexen‐1‐ol showed greater luring effects on male and female C. lapathi compared with the control. Turpentine oil was stronger repellent, and geraniol showed stronger luring effects on male C. lapathi than the control. Wind tunnel assays with both male and female C. lapathi indicated that salicylaldehyde, α‐pinene, and turpentine oil elicited repellent effects compared with the control. Linoleic acid, (Z)‐3‐hexen‐1‐ol, and geraniol were stronger lures of both male and female C. lapathi than the control. These results provide a basis for the further development of C. lapathi luring and repellent agents.     

Electroantennographic responses of red flour beetle Tribolium castaneum Herbst (Coleoptera: Tenebrionidae) to volatile organic compounds

The red flour beetle Tribolium castaneum Herbst (Coleoptera: Tenebrionidae) is the most encountered and destructive stored product insect pest of cereal grains and seeds. Although this beetle has been used as a model organism for many decades, there is no systematic knowledge about antennal detection of host and non‐host volatiles. Electroantennogram responses to 94 selected volatile organic compounds including alkanes, alkenes, alcohols, aldehydes, ketones, carboxylic acids, esters, terpenoids and aromatic compounds were recorded from both sexes of T. castaneum. Overall, female and male T. castaneum exhibited similar electroantennography (EAG) responses. Compounds eliciting the strongest EAG responses within compound groups of chemical similarity were undecane, 1‐hexen‐3‐ol, octanal, 2‐heptanone, hexanoic acid and ethyl hexanoate. Comparison of vapour pressure and EAG amplitudes within homologous series of compounds revealed responses to undecane, octadecane, octanal, nonanal, 2‐heptanone, hexanoic acid and octanoic acid as outstanding. Given that systematic EAG screenings have not been conducted before, these are the best candidates for evaluation in future behavioural studies to unravel their potential for application in integrated pest management strategies of T. castaneum.     

Plant volatiles in the sexual communication of Melolontha hippocastani: response towards time-dependent bouquets and novel function of (Z)-3-hexen-1-ol as a sexual kairomone

1. Swarming males of Melolontha hippocastani are known to locate females that stay feeding within the host trees by orienting towards damage‐induced plant volatiles (green leaf volatiles) and a sex pheromone. Thus, volatiles emitted by freshly damaged leaves might indicate to a male the presence of currently feeding females. 2. The hypothesis was studied that volatiles from freshly damaged leaves are more attractive to males than volatiles from old damaged leaves. The odour bouquets of damaged leaves from three plant species that have been shown to attract male M. hippocastani in the field were analysed 10 min (fresh damage) and 1.5 h (old damage) after damaging, using coupled gas chromatography–mass spectrometry. The results showed clear differences between the bouquets: the bouquet of freshly damaged leaves of all species consisted of typical leaf aldehydes, i.e. hexanal, (Z)‐3‐hexenal, (Z)‐2‐hexenal, (E)‐2‐hexenal, the leaf alcohol (Z)‐3‐hexen‐1‐ol, and the corresponding acetate. One and a half hours after damage, aldehydes had almost vanished and (Z)‐3‐hexen‐1‐ol and (Z)‐3‐hexenyl acetate predominated; however males of M. hippocastani were equally attracted to traps baited with volatiles from old and freshly damaged leaves in field experiments. When traps were baited with synthetic volatile mixtures mimicking the bouquets of old and freshly damaged leaves, M. hippocastani males even preferred the old damage mixture. 3. Experiments addressing the role of individual green leaf volatiles revealed that only (Z)‐3‐hexen‐1‐ol was highly attractive while the other compounds tested individually were behaviourally inactive, however all tested compounds elicited comparable electrophysiological responses on male M. hippocastani antennae. 4. In analogy to the term aggregation kairomone used for feeding‐induced plant volatiles that attract both sexes of an insect, the term sexual kairomone is suggested to describe the novel function of (Z)‐3‐hexen‐1‐ol in the sexual communication of M. hippocastani.     

Molecular and functional characterization of three odorant‐binding proteins from the wheat blossom midge,Sitodiplosis mosellana

Sitodiplosis mosellana, a periodic but devastating wheat pest, relies on wheat spike volatiles as a cue in selecting hosts for oviposition. Insect odorant‐binding proteins (OBPs) are thought to play essential roles in filtering, binding and transporting hydrophobic odorant molecules to specific receptors. To date, the molecular mechanisms underlying S. mosellana olfaction are poorly understood. Here, three S. mosellana antenna‐specific OBP genes, SmosOBP11, 16 and 21, were cloned and bacterially expressed. Binding properties of the recombinant proteins to 28 volatiles emitted from wheat spikes were investigated using fluorescence competitive binding assays. Sequence analysis suggested that these SmosOBPs belong to the Classic OBP subfamily. Ligand‐binding analysis showed that all three SmosOBPs preferentially bound alcohol, ester and ketone compounds, and SmosOBP11 and 16 also selectively bound terpenoid compounds. In particular, the three SmosOBPs had high binding affinities (K_i < 20 μmol/L) to 3‐hexanol and cis‐3‐hexenylacetate that elicited strong electroantennogram (EAG) response from female antennae. In addition, SmosOBP11 displayed significantly higher binding (K_i < 8 μmol/L) than SmosOBP16 and 21 to 1‐octen‐3‐ol, D‐panthenol, α‐pinene and heptyl acetate which elicited significant EAG response, suggesting that SmosOBP11 plays a major role in recognition and transportation of these volatiles. These findings have provided important insight into the molecular mechanism by which S. mosellana specifically recognizes plant volatiles for host selection, and have facilitated identification of effective volatile attractants that are potentially useful for pest monitoring and trapping.     

Behavioural and electrophysiological responses of females of two species of tabanid to volatiles in urine of different mammals

Urine volatiles from different ungulates (cows, horses and sheep) were tested as bait for tabanids in southeastern France using Nzi traps during the early summer of 2011. Tabanus bromius Linnaeus, 1758 and Atylotus quadrifarius (Loew, 1874) (both: Diptera: Tabanidae) were the most captured species, respectively representing 57% and 41% of all tabanids collected (all of which were female). Horse urine significantly increased catches of T. bromius (1.6‐fold) and A. quadrifarius (3.5‐fold), and sheep urine significantly increased catches of A. quadrifarius (2.5‐fold). In parallel, an electroantennogram (EAG) study was conducted for the first time on these two species, in which EAGs were recorded using 1‐octen‐3‐ol and extracts of the same urine samples used in the field. For T. bromius, the EAG response to 1‐octen‐3‐ol increased quasi‐sigmoidally with dose, with a maximum response at ≥100 µg on filter paper. For both species of tabanid, cow and horse urine elicited larger EAGs than did sheep urine. The behavioural implications in host‐seeking and feeding habits are discussed.     

Olfactory antennal responses to plant volatiles in apterous virginoparae of the vetch aphidMegoura viciae

Electroantennogram (EAG) responses were recorded from apterous virginoparae of the vetch aphidMegoura viciae Buckton (Homoptera, Aphididae) to more than eighty volatile compounds in order to investigate its sensory ability to perceive plant odours. The response profile ofM. viciae reveals a differential sensitivity for the array of plant volatiles tested. The whole group of general green leaf volatiles is very stimulatory. In addition to (E)-2-hexenal, the following compounds of this group elicit large EAG responses: (E)-2-heptenal, 1-octenol-3, hexyl acetate, (Z)-3-hexenyl acetate, hexanol-1, hexanal, 2-heptanone and 3-octanone. Relatively large EAGs are also produced by 4-methoxybenzaldehyde (p-anisaldehyde), hexanonitrile, heptanonitrile, 1,6-hexanedithiol, butyl isothiocyanate, 4-pentenyl isothiocyanate, (−)-(1S)-β-pinene, (+)-(S)-carvone, (−)-(R)-carvone, α-terpineol, linalool and citronellal. The nitriles are the most effective of all plant volatiles tested. Structure-activity relationships occur in various groups of chemicals and members of the green leaf volatiles, benzaldehydes, isothiocyanates and monoterpenes are ranked accordingly. In the group of green leaf volatiles, aliphatic aldehydes are more stimulating than the corresponding alcohols. EAG responses to series of saturated aliphatic alcohols and aldehydes reveal that C₆ and C₇ compounds are the most stimulatory. Dose-response curves show that the rank order of EAG response amplitudes hardly changes at lower dosages. It is concluded thatM. viciae perceives general plant volatiles as well as more-specific components, such as nitriles and isothiocyanates, associated with the odour blends of non-host plant species.     

Electroantennogram responses of aphid nymphs to plant volatiles

Abstract. Electroantennogram (EAG) responses of immature aphids were investigated for 30 plant volatile compounds in third‐ and fourth‐stadium nymphs of the black bean aphid, Aphis fabae. The nymphs were destined to develop into adult alate (winged) virginoparae. The EAG response profiles were similar to those previously reported in the adults. Among the compounds tested, hexanonitrile elicited the largest EAG responses in both nymphal stadia, corresponding to previously reported results with adults. Six‐carbon aliphatic compounds showed relatively higher EAG activities in the nymphs but, in contrast, (E)‐2‐hexenal, benzaldehyde, α‐pinene and β‐pinene, and citronellal elicited relatively smaller EAG responses in nymphs than adults. Although overall EAG response profiles were similar between the third and the fourth stadia for the majority of the volatiles, four aldehyde compounds, hexanal (E)‐2‐heptenal, 2‐hydroxybenzaldehyde and citronellal, showed relatively higher EAG activities in the third than in the fourth stadium. The present study indicates that aphid nymphs possess a functional olfactory receptor system before the antennae are fully developed morphologically and physiologically.     

Physiological state influences the antennal response of Anastrepha obliqua to male and host volatiles

The sexual and host‐related behaviours of the fruit fly Anastrepha obliqua Macquart (Diptera: Tephritidae) are mediated by volatile compounds. However, whether the physiological state of this species affects its antennal and behavioural responses to semiochemicals is unknown. The effects of age, mating status, diet and the topical application of methoprene, a Juvenile hormone analogue (JHA), on the antennal sensitivity of this tephritid fruit fly species to selected male [(Z)‐3‐nonenol] and host fruit volatiles (ethyl benzoate, ethyl hexanoate, ethyl butyrate and trans‐β‐ocimene) are investigated using electroantennography (EAG). Overall, (Z)‐3‐nonenol and ethyl benzoate elicit the highest EAG responses in both sexes. Flies of both sexes aged 1, 5 and 10 days old show higher EAG responses to the tested compounds compared with flies aged 20 days old. Virgin females and males show higher EAG responses to volatile compounds than mated flies. Females and males fed with sugar plus protein show higher antennal responses to volatiles compared with flies fed sugar or protein alone. Flies of both sexes treated with methoprene show higher antennal responses than flies treated with acetone (control). These results suggest that the peripheral olfactory system in A. obliqua is modulated by the physiological state of the flies.     

Study of the Vapor Phase Over Fusarium Fungi Cultured on Various Substrates

The compositions of volatile organic compounds (VOCs) emitted by Fusarium fungi (F. langsethiae, F. sibiricum, F. poae, and F. sporotrichioides) grown on two nutritive substrates: potato sucrose agar (PSA) and autoclaved wheat kernels (WK) were investigated. The culturing of fungi and study of their VOC emissions were performed in chromatographic vials at room temperature (23 – 24 °C) and the VOCs were sampled by a solid‐phase microextraction on a 85 μm carboxen/polydimethylsiloxane fiber. GC/MS was performed using a 60‐m HP‐5 capillary column. Components of the VOC mixture were identified by electron impact mass spectra and chromatographic retention indices (RIs). The most abundant components of the VOC mixture emitted by Fusarium fungi are EtOH, AcOH, ⁱBuOH, 3‐methylbutan‐1‐ol, 2‐methylbutan‐1‐ol, ethyl 3‐methylbutanoate, terpenes with M 136, sesquiterpenes with M 204 (a total of about 25), and trichodiene. It was found that the strains grown on PSA emit a wider spectrum and larger amount of VOCs compared with those grown on wheat kernels. F. langsethiae strain is the most active VOC producer on both substrates. The use of SPME and GC/MS also offers the potential for differentiation of fungal species and strains.     

棉铃虫齿唇姬蜂对植物挥发物和寄主性信息素腺体化合物的EAG反应

测试了棉铃虫齿唇姬蜂Campoletis chlorideae Uchida对58种植物挥发物和5种寄主性信息素腺体化合物的EAG反应。在100 μg的刺激剂量下,棉铃虫齿唇姬蜂对C₅～C₇脂肪醇的EAG反应最强,碳链延长或缩短都将导致反应的降低;对脂肪醛、酮、酸和酯都有一定的反应。棉铃虫齿唇姬蜂对萜烯的EAG反应很低,对氧化萜的反应普遍升高。3种芳香化合物均可激起棉铃虫齿唇姬蜂较强的EAG反应。剂量反应曲线表明,具有EAG活性的化合物激起的反应强度与化合物的剂量呈正相关,而2种萜烯——α-蒎烯和反式石竹烯,在测定的剂量范围内EAG活性都很低。棉铃虫齿唇姬蜂对寄主性信息素腺体化合物也有EAG反应,用100 μg和1 000 μg的寄主性信息素刺激,雄蜂的反应可比雌蜂的反应高出1倍。对植物挥发物在棉铃虫齿唇姬蜂寻找寄主中的作用进行了讨论。     

Electroantennogram responses to plant volatiles in two species of Pieris butterflies

Electroantennogram (EAG) responses were recorded from females of two related butterfly species, Pieris brassicae L. and P. rapae L. (Lepidoptera: Pieridae) to 23 volatiles of plant origin, 19 of which have been reported to occur in the headspace of their preferred host plants, Brassica and Sinapis species (Cruciferae). In both species, selective responses were observed and the most effective compounds were the 6-carbon fatty acid derivatives trans-hex-2-enal, hexan-1-ol and hexanal, which are common green leaf volatiles. Of the 6 isoprenoids tested, myrcene and geraniol were most effective. Of the 4 crucifer-specific compounds tested, phenylacetonitrile was a distinctly stronger stimulant than the three isothiocyanates in both species. The rank order of mean stimulating effectiveness of all compounds tested was strongly correlated between the two species. Statistical analysis of dose-response relationships for 6 compounds revealed significant differences between compounds. The rank order of effectiveness changed with dose. Exclusive exposure to Sinapis arvensis during larval life and young adulthood resulted in quantitative changes in EAG responses to several compounds in both species, although the overall rank order of effectiveness was strongly correlated between the groups reared on the two host plants.     

Thuja occidentalis: identification of volatiles and electroantennographic response by the invasive cedar bark beetle,Phloeosinus aubei

Recently, the distribution of the Mediterranean cedar bark beetle, Phloeosinus aubei Perris (Coleoptera: Scolytidae), has expanded to Central Europe. Reported mostly on cypress in the Mediterranean area, potential host plants in the invaded range include other scale‐leafed conifers, such as cultivars of arborvitae, Thuja occidentalis L. To reveal potential kairomonal cues for P. aubei, volatiles of T. occidentalis were collected and analysed by gas chromatography with electroantennographic detection (GC‐EAD). Assignments of chemical structures of antennally active components were carried out by gas chromatography linked to mass spectrometry (GC‐MS) using authentic reference samples. Antennal responses to synthetic samples of the identified compounds were studied by electroantennography (EAG), with antennae of female and male P. aubei. GC‐EAD analysis of head space volatiles of T. occidentalis revealed 22 antennally active compounds, of which 21 were identified. The most abundant components were α‐ and β‐thujone, fenchone, camphor, terpinen‐4‐ol, bornyl acetate and α‐terpinyl acetate, all of which are oxygenated monoterpenes. When EAG activities of synthetic samples were compared, the most intensive responses from female antennae were elicited by a mixture of α‐ and β‐thujone, followed by (–)‐terpinen‐4‐ol, (+)‐camphor, cis‐4‐thujanol, (+)‐sabina ketone, (+)‐terpinen‐4‐ol, isopulegone, (–)‐fenchone, borneol, (3Z)‐hexen‐1‐ol, (–)‐1‐octen‐3‐ol and (+)‐sulcatol. Male antennae responded the most to (–)‐terpinen‐4‐ol and cis‐4‐thujanol followed by the mixture of α‐ and β‐thujone. The next highest responses were elicited by (+)‐camphor, borneol, (+)‐terpinen‐4‐ol, (+)‐sulcatol and (+)‐sabina ketone. Striking differences were found between responses to the enantiomers of fenchone, sulcatol and 1‐octen‐3‐ol, whereas responses to the enantiomers of terpinen‐4‐ol did not differ significantly from each other. Several antennally active volatiles of T. occidentalis have also been reported from cypress and various other members of the Cupressaceae, suggesting that the sensory apparatus of P. aubei may recognize the shared components, which may enable rapid adaptation to new hosts in the invaded areas.     

Electroantennogram and behavioral responses of Cotesia plutellae to plant volatiles

Plant volatiles have been demonstrated to play an important role in regulating the behavior of Cotesia plutellae, a major larval parasitoid of the diamondback moth (DBM), Plutella xylostella, but little is currently known about the function of each volatile and their mixtures. We selected 13 volatiles of the DBM host plant, a cruciferous vegetable, to study the electroantennogram (EAG) and behavioral responses of C. plutellae. EAG responses to each of the compounds generally increased with concentration. Strong EAG responses were to 100 μL/mL of trans‐2‐hexenal, benzaldehyde, nonanal and cis‐3‐hexenol, and 10 μL/mL of trans‐2‐hexenal and benzaldehyde with the strongest response provoked by trans‐2‐hexenal at 100 μL/mL. In the Y‐tube olfactometer, C. plutellae, was significantly attracted by 1 μL/mL of trans‐2‐hexenal and benzaldehyde. β‐caryophyllene, cis‐3‐hexenol or trans‐2‐hexenal significantly attracted C. plutellae at 10 μL/mL, while nonanal, benzyl alcohol, cis‐3‐hexenol or benzyl cyanide at 100 μL/mL significantly attracted C. plutellae. Trans‐2‐hexenal significantly repelled C. plutellae at 100 μL/mL. EAG of C. plutellae showed strong responses to all mixtures made of five various compounds with mixtures 3 (trans‐2‐hexenal, benzaldehyde, nonanal, cis‐3‐hexenol, benzyl cyanide, farnesene, eucalyptol) and 4 (trans‐2‐hexenal, benzaldehyde, benzyl alcohol, (R)‐(+)‐limonene, β‐ionone, farnesene, eucalyptol) significantly attracting C. plutellae. These findings demonstrate that the behavior of C. plutellae can be affected either by individual compounds or mixtures of plant volatiles, suggesting a potential of using plant volatiles to improve the efficiency of this parasitoid for biocontrol of P. xylostella.