EAD-active Compounds Research Articles

Identification of the Sex Pheromone of the Asparagus Moth, Parahypopta Caestrum (Lepidoptera, Cossidae)

Chemical, electrophysiological, and field trapping experiments were carried out to identify the female-produced sex pheromone of the asparagus moth, Parahypopta caestrum, a very serious pests of asparagus cultivations in southern Europe. Gas chromatography coupled with mass spectrometry and electroantennogram detection (GC-MS-EAD) analysis of hexane and solid-phase microextraction (SPME) extracts of sex pheromone glands of calling females consistently detected four compounds eliciting EAG responses in male moth antennae. According to their GC retention times, mass spectra, and comparative EAG analyses with reference standards, these EAD-active compounds were identified as (Z)-9-tetradecenol (Z9-14:OH), (Z)-5-tetradecenyl acetate (Z5-14:Ac), (Z)-7-tetradecenyl acetate (Z7-14:Ac), and (Z)-9-tetradecenyl acetate (Z9-14:Ac), respectively. In the SPME extracts from the head-space of individual abdominal tips, Z9-14:Ac, Z5-14:Ac, Z7-14:Ac, and Z9:14 OH were detected in the ratio of 82:9:5:4. In EAG dose-response experiments, Z9-14:Ac was the strongest antennal stimulant at different doses tested. In field trapping experiments, Z9-14:Ac, Z7-14:Ac, and Z5-14:Ac proven to be essential for male attraction and a their 85:5:10 blend loaded onto green rubber septum dispensers was significantly more effective than single-, two-, and any other three-component blend of these compounds. The addition of Z9-14:OH to the optimal blend resulted in a significant reduction of male catches. The attractive blend here identified allowed for an effective and accurate monitoring of P. caestrum flight activity in southern Italy.

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.

Quantitative analysis and characterization of floral volatiles, and the role of active compounds on the behavior of Heortia vitessoides.

This study explores the role of floral volatile organic compounds (FVOCs) in insect behavior, focusing on Aquilaria sinensis (AS), a valuable tropical plant threatened by Heortia vitessoides Moore. Despite H. vitessoides' attraction to AS and non-host plants like Elaeocarpus decipiens (ED) and Dalbergia odorifera (DO), little is known about their chemical interactions. FVOCs from these plants were analyzed at 9:00 and 18:00 using GC×GC-QTOF-MS and HS-SPME. The results showed that ED exhibiting the highest concentration (92.340 ng/mg), followed by DO (75.167 ng/mg) and AS (64.450 ng/mg). Through GC-EAD and EAG, a total of 11 FVOC compounds with electrophysiological activates were identified. These compounds, except linalool, showed dose-dependent responses. Y-Tube bioassays confirmed phenylethyl alcohol or the mixture of EAD-active compounds produced positive chemotactic responses in both males and females. FVOCs have the potential to be used as a natural and sustainable alternative to chemical insecticides in pest control.

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.

Colletes hederae bees are equally attracted by visual and olfactory cues of inconspicuous Hedera helix flowers

Wild bees are heavily declining worldwide except for a few species, such as Colletes hederae, which is spreading in its distribution throughout Europe. Colletes hederae mainly forages on ivy (Hedera helix) which is widespread in Europe and the plants’ availability is thought to contribute to the successful spread of C. hederae. A rapid location of the plants using visual and/or olfactory floral cues would allow the bee to efficiently forage. Beside bee visitors, the flowers attract a high variety of other insects, such as Vespula wasps that were recently investigated regarding their floral-cue preferences. The aim of this study was to investigate the communication between C. hederae and its H. helix host flowers, and to compare the results with that previously obtained with V. germanica wasps. We identified headspace compounds detectable by the bees using gas chromatography coupled to electroantennography (GC-EAD) and performed behavioral experiments to both compare the attractiveness of visual and olfactory floral cues and to determine the attractiveness of a synthetic mixture composed of physiologically active compounds. In the GC-EAD analyses, bees responded to 15 flower-specific compounds of various chemical classes, of which 4-oxoisophorone, (E)-linalool-oxide furanoid, and acetophenone were the most abundant in the floral scent. In the bioassays, visual and olfactory flower cues were equally attractive for bees, but a combination of both cues was needed to elicit not only approach responses but also landings. A synthetic mixture of the EAD-active compounds was attractive to the bees, but to a lesser extent than the natural scent of H. helix flowers. The bees’ integrations of different floral-cue modalities in its search image and its strong antennal responses elicited by various floral scent compounds make C. hederae highly effective in finding its host flowers. In comparison to V. germanica wasps, the bees relied stronger on visual cues than the wasps do, but both species showed the highest attraction when presented with a combination of the cues.

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.

Sea Buckthorn Hippophae rhamnoides and Fruit Flies Rhagoletis batava: Search for Volatile Semiochemicals Involved in Pest Attraction

Rhagoletis batava (Diptera: Tephritidae), is the most important pest of Hippophae rhamnoides fruits. For detection and monitoring of R. batava, traps supplied with nonspecific attractants are used. Thus, new, more specific attractants for environment-friendly pest control are needed. Such attractants could be fruit-related semiochemicals that are involved in the host location by flies. Behavioural Y-olfactometer tests revealed that R. batava males were attracted to ripe fruit odour, while females preferred unripe and semi-ripe fruits. Thermal desorption gas chromatography-mass spectrometry (GC-MS) analysis revealed substantial quantitative and qualitative changes in volatiles between unripe and ripe fruits. In the unripe fruit emission, 41 volatile compounds were isolated, whereas 64 compounds were sampled from the ripe fruits. The total amount of volatiles increased five times during the fruit ripening. Gas chromatography-electroantennogram detection (GC-EAD) and GC-MS analyses of the fruit headspace volatiles revealed at least 26 compounds in unripe and 27 compounds in ripe fruits eliciting antennal responses of R. batava for both sexes. The fruits of these two ripening stages differed qualitatively in the single EAD-active compound only, i.e., 3-methylbutyl 2-methylpropionate. Esters were the most abundant volatiles, composing 84% and 93% of EAD-active compounds in the emissions of unripe and ripe fruits, respectively. Based on the persistent EAG responses, 17 compounds were selected as the most promising candidates for kairomone attractants of the sea buckthorn pest R. batava.

Courtship behavior and identification of a sex pheromone in Ibalia leucospoides (Hymenoptera: Ibaliidae), a larval parasitoid of Sirex noctilio (Hymenoptera: Siricidae).

BackgroundIbalia leucospoides (Hymenoptera: Ibaliidae) is a larval parasitoid that has been widely introduced as a biological control agent for the invasive woodwasp,Sirex noctilio (Hymenoptera: Siricidae) in the Southern Hemisphere. In this study, the courtship behavior and identificaion of sex pheromones are described for I. leucospoides under laboratory conditions.MethodsFor courtship behavior, both sexes were observed in a wire mesh observation cylinder (75 cm length ×10 cm diameter) for 15 minutes. The female body washes were analyzed using Gas Chromatography- Electroantennographic Detection (GC-EAD). Then the EAD-active compounds were tentatively identified using GC-Mass Spectrometry (GC-MS) and examined in olfactometer assays.ResultsThe courtship behavior included rhythmic lateral movements, mounting, head-nodding cycles in males, and wing-fanning in females. GC-EAD analysis of female body washes with male antennae revealed seven compounds which elicited antennal responses, four of which are straight-chain alkanes (C23, C25, C26, and C27). The identities of these alkanes were confirmed by matching the retention times, mass spectra, and male antennal activity to those of commercially obtained chemicals. In olfactometer assays, a blend of the four straight-chain alkanes was attractive to I. leucospoides males, and there was no response to blends that lacked any of these four compounds. Female body wash was no more attractive than the four-component blend. The ratios of EAD-active components differ between hydrocarbon profiles from males and females.ConclusionThis study is the first investigation of cuticular hydrocarbons in the family Ibaliidae. It provides evidence that the ubiquitous alkanes (C23, C25, C26, and C27) in sex-specific ratios attract I. leucospoides males.

Antennal and Behavioral Responses of Drosophila suzukii to Volatiles from a Non-Crop Host, Osyris wightiana.

Simple SummaryThe spotted-wing drosophila Drosophila suzukii, native to Southeast Asia, has become a new threat for cultivated and wild soft-skinned fruits in both their native and invaded areas. The attractiveness of volatiles from fresh ripening and ripe fruits of cultivated crops, such as raspberry, blueberry, strawberry, and cherry, has been extensively studied. To date, however, little attention has been paid to the non-crop host of D. suzukii. In this study, we collected headspace volatiles from ripe fruits of a wild non-crop host, Osyris wightiana, and identified seven compounds attractive to D. suzukii from the fruit volatiles. A blend of the seven active compounds captured a significant amount of female and male D. suzukii in field, suggesting that the blend can be used to develop an attractant for management and monitoring of D. suzukii.Drosophila suzukii (Diptera: Drosophilidae) infests a variety of commercial fruits, including cherries and other soft-skinned fruits. After the cropping season of most cultivated crop hosts, it heavily infests the fruit of a wild host-plant, Osyris wightiana in southwest China. Here, we employ gas chromatography-electroantennographic detection (GC-EAD) together with behavioral bioassays and a trapping experiment to identify volatile semiochemicals emitted by O. wightiana that are involved in D. suzukii attraction. GC-EAD recordings of D. suzukii antenna showed responses to 13 compounds, including α-pinene, 3-methylbutyl acetate, 2-hexanol, E-β-ocimene, Z-3-hexenol, β-caryophyllene, α-humulene, and six unidentified compounds. The flies were attracted by seven individual EAD-active compounds at low doses (0.01 and 0.1 μg), but were repelled at high doses (10 and 100 μg). In a similar manner, a blend of seven EAD-active compounds at low doses (0.1 and 1 μg) was attractive to female flies, but became repulsive at high doses (10 μg). The low dose of the blend was as attractive as the fruit volatiles, although both were less attractive than the fruits. The blend attracted both female and male D. suzukii and other Drosophila flies. The percentage of D. suzukii out of all flies captured by the blend was significantly greater than that captured by the control. These results indicate that the EAD-active volatile compounds emitted by fruits of O. wightiana play an important role in D. suzukii attraction, and have the potential to be used for management of D. suzukii.

Limoniic Acid - Major Component of the Sex Pheromones of the Click Beetles Limonius canus and L. californicus.

Wireworms, the larvae of click beetles (Coleoptera: Elateridae), are soil-dwelling insect pests inflicting major economic damage on many types of agricultural crops worldwide. The objective of this work was to identify the female-produced sex pheromones of the Pacific Coast wireworm, Limonius canus LeConte, and the sugarbeet wireworm, L. californicus (Mannerheim) (Coleoptera: Elateridae). Headspace volatiles from separate groups of female L. canus and L. californicus were collected on Porapak Q and analyzed by gas chromatography with electroantennographic detection (GC-EAD) and GC-mass spectrometry. GC-EAD recordings revealed strong responses from male L. canus and male L. californicus antennae to the same compound, which appeared below GC detection threshold. The structure of this candidate pheromone component was deduced from the results of micro-analytical treatments of extracts, retention index calculations on four GC columns, and by syntheses of more than 25 model compounds which were assessed for their GC retention characteristics and electrophysiological activity. The EAD-active compound was identified as (E)-4-ethyloct-4-enoic acid, which we name limoniic acid. In field experiments in British Columbia and Alberta, Canada, traps baited with synthetic limoniic acid captured large numbers of male Limonius click beetles, whereas unbaited control traps captured few. Compared to traps baited with the analogue, (E)-5-ethyloct-4-enoic acid, traps baited with limoniic acid captured 9-times more male L. californicus, and 6.5-times more male western field wireworms, L. infuscatus Motschulsky, but 2.3-times fewer male L. canus. Limoniic acid can now be developed for detection, monitoring and possibly control of L. californicus, L. infuscatus and L. canus populations.

Fruit volatiles mediate differential attraction of Drosophila suzukii to wild and cultivated blueberries

Native to the northeast USA, highbush blueberry is a crop domesticated for close to 100 years and that has been selected mainly for high yields and bigger fruit. We hypothesized that, due to domestication and associated agronomic selection (i.e., cultivation practices), cultivated blueberries differ from their wild ancestors in fruit volatile emissions, affecting the response of a frugivorous pest. To test this hypothesis, we compared the attraction of adult spotted-wing drosophila (Drosophila suzukii) to wild and cultivated blueberry fruit volatiles in choice assays. We also conducted headspace volatile chemical analysis and electroantennographic detection (EAD) analysis to identify and quantify any antennally active compounds. For this, fruit from wild and cultivated blueberries, growing in proximity, was sampled from six farms located in the Pinelands National Reserve (New Jersey, USA)—a blueberry-producing region with a forest understory consisting largely of wild blueberries. On a per gram basis, we found that wild blueberries are more attractive to D. suzukii flies and have higher volatile emission rates than cultivated blueberries. Nine EAD-active compounds from wild blueberries (isobutyl acetate, ethyl butyrate, ethyl 2-methylbutyrate, ethyl 3-methylbutyrate, hexanal, isoamyl acetate, 3-hydroxybutanone (acetoin), 6-methyl-5-hepten-2-one, and 1-hexanol) were attractive individually and as a blend to D. suzukii flies. However, a 4-component blend composed of isoamyl acetate, acetoin, 6-methyl-5-hepten-2-one, and 1-hexanol was more attractive to D. suzukii than the 9-component blend. Altogether, our results show that the domestication/cultivation of blueberries is associated with lower rates of fruit volatile emissions, which has resulted in decreased attraction of a frugivorous pest, D. suzukii.

Peach volatile emission and attractiveness of different host plant volatiles blends to Cydia molesta in adjacent peach and pear orchards

The oriental fruit moth (OFM), Cydia (= Grapholitha) molesta, is a highly damaging pest; peaches are its primary host, and pears serve as post-peach secondary hosts during the late season in China. We collected volatiles from detached peach shoots and fruits, and identified them with gas chromatography–mass spectrometry (GC–MS). Antennally active compounds were identified by gas chromatography-electroantennogram detection (GC-EAD), and these were further tested in the laboratory and field. We detected consistent electroantennographic activity was for ten compounds. Significantly more C. molesta females were caught with a mixture of female EAD-active compounds identified from the detached matured peach fruits (nonanal, butyl acetate, 3-methylbutyl acetate, hexyl acetate, (Z)-3-hexenyl acetate, linalool and farnesene) than other mixtures mimicking the volatile profile from detached matured fruits or shoots. We identified a new GC-EAD active mixture from intact peach shoots composed of nonanal, (Z)-3-hexenyl acetate, (E)-β-ocimene, and 6-methyl-5-hepten-2-one. In the field test, the background odour of orchards could affect trap catches, and two peach-derived blends together with two previously known pear-derived blends were proven to be able to monitor the seasonal OFM population dispersal in adjacent orchards. These host plant blends will be effective for further designing candidate attractants for season-long C. molesta population dynamic monitoring.

Behavioral Responses of Scolytus schevyrewi (Coleoptera: Curculionidae: Scolytinae) to Volatiles From Apricot Tree (Rosales: Rosaceae).

Scolytus schevyrewi Semenov (Coleoptera: Curculionidae: Scolytinae) is native to China and Central Asia. Damage by the adults and larvae weakens local apricot trees (Armeniaca spp.), often causing death to many host trees. In previous studies, freshly cut apricot logs were found to be highly attractive to S. schevyrewi adults. To explore the possibility of trapping and monitoring this bark beetle, we evaluated the effect of the apricot tree volatiles on S. schevyrewi behavior. Volatiles from the apricot logs were collected by headspace sampling and subjected to coupled gas chromatography-electroantennographic detection (GC-EAD) analysis. Behavioral responses to EAD-active compounds were assessed using two-choice Y-tube olfactometers. The results showed that the antennae of females responded to 21 volatile compounds from apricot logs. Seventeen compounds were confirmed with authentic compounds. The Y-olfactometer bioassays showed that at a stimulation dose of 100 µg, four compounds [(1S)-(-)-α-pinene, (±)-limonene, (1S)-(+)-3-carene, and 1-hexanol], and some binary mixtures of the four compounds [(1S)-(-)-α-pinene plus (±)-limonene; (1S)-(-)-α-pinene plus (1S)-(+)-3-carene; (1S)-(-)-α-pinene plus camphene; (1S)-(-)-α-pinene plus (±)-limonene, (1S)-(+)-3-carene, and 1-hexanol] were significantly attractive to both sexes (except (±)-limonene and (1S)-(+)-3-carene for males), suggesting that these compounds may play a role in host tree selection by S. schevyrewi and should be evaluated as lures for population monitoring. In contrast, octanal, nonanal, decanal, linalool and N,N-diethylformamide appeared to repel S. schevyrewi adults in Y-tube at the concentration tested.

Electrophysiological and Behavioral Responses of Queensland Fruit Fly Females to Fruit Odors.

Females of the Queensland fruit fly (QFF), Bactrocera tryoni, are amongst the most damaging pests of horticulture in Australia and neighboring countries. Females can lay eggs into more than a hundred species of fruits and vegetables, resulting in large crop losses. Sexually mature males can be managed sustainably with traps baited with long-lasting synthetic lures, and sexually immature males and females can be attracted and killed by short-lived protein baits applied directly on surfaces, with a low success rate (< 20%). No long-lasting attractants for virgin or mated females exist. With the aim of developing a female attractant for surveillance, we collected and analyzed the odors of four ripe host fruits: orange, cherry guava, banana and feijoa. Virgin and mated female QFF were tested with gas-chromatography coupled with electro-antennographic detection to identify electrophysiologically (EAD)-active compounds. We detected 41 EAD-active compounds, with seven found common for more than one fruit. Overall, mated females responded more often and with higher intensity than virgin females. In particular, five compounds present either in cherry guava or feijoa triggered a significantly higher EAD response from mated females than from virgins. Twenty-six EAD-active compounds were selected and tested individually in a Y-tube olfactometer to measure attraction of both virgin and mated females. Behavioral responses differed significantly amongst the compounds, but not strongly between virgin and mated females. We did not find any correlation between electrophysiological and behavioral responses. Further field testing with behaviorally-active compounds is needed for the development of a new QFF female lure.

Styrene, (+)-trans-(1R,4S,5S)-4-Thujanol and Oxygenated Monoterpenes Related to Host Stress Elicit Strong Electrophysiological Responses in the Bark Beetle Ips typographus

Bark beetles kill apparently vigorous conifers during epidemics by means of pheromone-mediated aggregation. During non-endemic conditions the beetles are limited to use trees with poor defense, like wind-thrown. To find olfactory cues that help beetles to distinguish between trees with strong or weak defense, we collected volatiles from the bark surface of healthy felled or standing Picea abies trees. Furthermore, living trees were treated with methyl jasmonate in order to induce defense responses. Volatiles were analyzed by combined gas chromatography and electroantennographic detection (GC-EAD) on Ips typographus antennae. Compounds eliciting antennal responses were characterized by single sensillum recording for identification of specific olfactory sensory neurons (OSN). Release of monoterpene hydrocarbons decreased, while oxygenated compounds increased, from spring to early summer in felled trees. In both beetle sexes particular strong EAD activity was elicited by trace amounts of terpene alcohols and ketones. 4-Thujanol gave a very strong response and the absolute configuration of the tested natural product was assigned to be (+)-trans-(1R,4S,5S)-thujanol by stereoselective synthesis and enantioselective gas chromatography. One type of OSN responded to all ketones and five other OSN were characterized by the type of compounds that elicited responses. Three new OSN classes were found. Of the eight EAD-active compounds found in methyl jasmonate-treated bark, the known anti-attractant 1,8-cineole was the one most strongly induced. Our data support the hypothesis that highly active oxygenated host volatiles could serve as positive or negative cues for host selection in I. typographus and in other bark beetles.

Electrophysiological and Behavioral Responses of the Kudzu Bug, Megacopta cribraria (Hemiptera: Plataspidae), to Volatile Compounds from Kudzu and Soybean Plants.

The kudzu bug, Megacopta cribraria, is a key pest of soybean in the United States. Electrophysiological and behavioral responses of adult M. cribraria to kudzu and soybean volatile compounds were examined to identify semiochemicals used for host location. Headspace volatiles collected from undamaged potted plants were analyzed by gas chromatography with electroantennographic detection (GC-EAD). Subsequently, six GC-EAD-active compounds were identified by gas chromatography-mass spectrometry (GC-MS). These six compounds, along with some previously reported insect attractants, were selected for electroantennogram (EAG) assays. The four chemicals that elicited the strongest EAG responses, 1-octen-3-ol, nonanal, benzaldehyde, and ocimene, were selected for evaluation in olfactometer bioassays. Both benzaldehyde and 1-octen-3-ol exhibited dose-dependent responses at higher concentration. Our results provide insight into host location compounds used by adult M. cribraria. These results may be evaluated in future field tests and ultimately useful to develop a semiochemical-based monitoring technique and integrated pest management program for M. cribraria.

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.

A female attractant for the blue gum chalcid, Leptocybe invasa (Hymenoptera: Eulophidae), from host plant (DH 201-2: Eucalyptus grandis × Eucalyptus tereticornis)

The blue gum chalcid, Leptocybe invasa, is a severe insect pest of Eucalyptus trees leading to gall formation, stunting, leaf deformation, and death in cases, China. In the previous studies, we found that the Eucalyptus hybrid, DH 201-2 (Eucalyptus grandis × Eucalyptus tereticornis), is highly preferred to L. invasa larvae and adults, but its mechanism has not been fully understood. In the present study, we investigated the volatile organic compounds (VOCs) from DH 201-2 that attract L. invasa. Volatiles were collected from fresh young leaves and identified with gas chromatography–mass spectrometry (GC–MS) and gas chromatography–electroantennogram detection (GC–EAD). The attraction of identified volatiles to L. invasa was then measured under laboratory and field conditions. Two EAD-active compounds, gamma-terpinene and Limonene, were identified. In the dose–response experiments, we found that the EAG response to L. invasa was enhanced with the increased concentration of EAD-active compounds, and gamma-terpinene showed the stronger EAG response than Limonene. Both four-arm olfactometer bioassays and field studies showed that the blend of gamma-terpinene and Limonene with a ratio of 8:2 significantly attracted more L. invasa as compared to other ratios. The potential use of these compounds in the control of L. invasa is ulteriorly discussed.

Oviposition Deterrents in Larval Frass of Potato Tuberworm Moth, Phthorimaea operculella (Lepidoptera: Gelechiidae).

The potato tuberworm moth (PTM) Phthorimaea operculella (Zeller) (Lepidoptera: Gelechiidae) is one of the most damaging pests of potato Solanum tuberosum L. in warm temperate and subtropical areas. Our previous experiment showed that extracts of larval frass of PTM deterred oviposition of conspecific females. In this study, we investigated the identification of chemicals in larval frass that were influencing the oviposition of PTM by behavioral bioassays and electroantennography analysis in the laboratory. Frass was collected from third and fourth instar larvae and combined analysis of gas chromatography coupled with electroantennography (GC-EAD) of dichloromethane extracts showed that eight compounds from larval frass extracts elicited repeatable antennal responses from mated females. Seven EAD-active compounds in frass volatile extract were identified by gas chromatography-mass spectrometry (GC-MS) as linoleic acid, octadecanoic acid, tricosane, pentacosane, heptacosane, nonacosane, and cholesterol. Oviposition bioassays indicated that frass extracts had a deterrent effect on egg laying, the deterrent activity increased with the concentration of frass extracts, and the threshold value for statistical significance in oviposition deterrence was in the range of 20-200mg frass per cage. Linoleic acid, pentacosane, heptacosane, nonacosane, and cholesterol in larval frass volatiles were found to play a key role in repelling oviposition in a dose-dependent manner. We suggest that the bioactive compounds in larval frass are responsible for repelling oviposition of PTM, and n-alkanes, especially pentacosane, strongly deter oviposition and may be considered as a potential oviposition deterrent for potential applications.

Identification of active components from volatiles of Chinese bayberry, Myrica rubra attractive to Drosophila suzukii

Drosophila suzukii (Diptera: Drosophilidae) is native to Southeast Asia and now has become a severe pest of several soft fruits in Europe and the Americas. It causes considerable damage to Chinese bayberry, Myrica rubra, in China. In the present study, we employed gas chromatograph–electroantennographic detection (GC–EAD) together with behavioural bioassays and trapping experiments to identify volatile semiochemicals emitted by Chinese bayberry attracting D. suzukii. Electrophysiological experiments revealed the presence of six EAD-active compounds from ripe bayberry fruits, including methyl (E)-3-hexenoate, methyl (E)-2-hexenoate, ethyl (E)-2-hexenoate, α-ylangene, α-humulene and an unidentified compound that elicited consistent antennal response. In two-choice bioassays, bayberry fruits attracted all responding flies, and significantly more flies responded to the volatile extract of bayberry fruits. Four EAD-active compounds were attractive to mated female D. suzukii at lower doses (0.01 and 0.1 µg), but showed repellency at higher doses (10 and 100 µg). Mixtures of these four compounds at different ratios attracted D. suzukii flies at all test doses (0.1, 1 and 10 µg). Both male and female flies were trapped by a mixture of synthetic methyl (E)-3-hexenoate, methyl (E)-2-hexenoate, ethyl (E)-2-hexenoate and α-humulene in a ratio of 1:1.3:1:6.4 in the field trapping experiment. Significantly more males than females were captured in the trap baited with the synthetic blend, and the percentages of D. suzukii captured out of all flies by the traps baited with lure were higher than that baited with blank control. Our findings may provide insights into the olfactory responses of D. suzukii to specific host plant volatiles, and contribute to further development of an effective lure for monitoring D. suzukii in the field.