Pea plant volatiles guide host location behaviour in the pea moth

Identification of plant volatiles that attract mated insect females for oviposition can provide important information about plant–insect relationships that can be used to develop pest control strategies involving manipulation of the female host search. Our study represents a first step towards identifying volatiles that affect the host location behaviour of the pea moth Cydia nigricana. The behaviours of virgin and mated males and females were analysed in cage experiments testing a two-choice situation at close range and in wind tunnel experiments evaluating upwind orientation over a distance. In both experimental setups, flowering pea plants constituted the most attractive phenological stage for mated females, with 58 % landing on such plants in the wind tunnel. Testing headspace extracts of different phenological stages of pea and of detached pea buds and flowers in the wind tunnel, mated females showed the highest landing responses to volatiles during flower development (budding 42 % and flowering 56 %) and from detached buds (46 %) and flowers (66 %). Volatile compounds collected from the various phenological stages of pea were analysed by gas chromatography–mass spectrometry, and the antennal responses to these headspace collections were evaluated by gas chromatography–electroantennography. Ten antennally active compounds were identified, nine of which were present in the headspace extracts of the whole pea plants at all tested phenological stages and in detached buds and flowers. Overall, our results demonstrate a clear link between host plant phenology, the corresponding plant odour, and the behaviour of mated C. nigricana females.     

Olfactory responses of Drosophila suzukii females to host plant volatiles

Drosophila suzukii Matsumura, an endemic pest in southeast Asia, has invaded Europe and the U.S.A. Unlike most of its closely related sibling species, the serrated ovipositor of D. suzukii permits ovipositing in undamaged fresh fruits. In the present study, volatiles are identified from host plants that are potentially involved in D. suzukii host recognition and oviposition behaviour. It is shown that mated females are attracted to volatiles emitted from intact fruits. The antennally‐active suite of compounds released from the fresh fruits is identified by gas chromatography coupled with electroantennographic detection, as well as gas chromatography‐mass spectrometry. In olfactometer bioassays, mated females are significantly attracted to an electroantennographically active volatile, isoamyl acetate, when tested at 10 µg of synthetic compound in a rubber septa, which has a release rate comparable to that of fresh fruits. In addition, a genomic survey shows that D. suzukii not only possesses the full repertoire of genes encoding odorant receptors activated by isoamyl acetate in D. melanogaster, but also that one of the genes, OR67a, is represented by five duplicated copies. These results indicate that D. suzukii uses olfactory cues to select oviposition sites. The identification of volatiles emitted by host fruits that attract D. suzukii may aid in the development of a selective and efficient synthetic lure for monitoring this pest. As a close relative of Drosophila melanogaster, D. suzukii provides a unique opportunity for understanding the physiological mechanisms involved in the shift of this species from use of rotten to ripe fruits for oviposition.     

Electroantennographic bioassay as a screening tool for host plant volatiles

Plant volatiles play an important role in plant-insect interactions. Herbivorous insects use plant volatiles, known as kairomones, to locate their host plant. When a host plant is an important agronomic commodity feeding damage by insect pests can inflict serious economic losses to growers. Accordingly, kairomones can be used as attractants to lure or confuse these insects and, thus, offer an environmentally friendly alternative to pesticides for insect control. Unfortunately, plants can emit a vast number volatiles with varying compositions and ratios of emissions dependent upon the phenology of the commodity or the time of day. This makes identification of biologically active components or blends of volatile components an arduous process. To help identify the bioactive components of host plant volatile emissions we employ the laboratory-based screening bioassay electroantennography (EAG). EAG is an effective tool to evaluate and record electrophysiologically the olfactory responses of an insect via their antennal receptors. The EAG screening process can help reduce the number of volatiles tested to identify promising bioactive components. However, EAG bioassays only provide information about activation of receptors. It does not provide information about the type of insect behavior the compound elicits; which could be as an attractant, repellent or other type of behavioral response. Volatiles eliciting a significant response by EAG, relative to an appropriate positive control, are typically taken on to further testing of behavioral responses of the insect pest. The experimental design presented will detail the methodology employed to screen almond-based host plant volatiles by measurement of the electrophysiological antennal responses of an adult insect pest navel orangeworm (Amyelois transitella) to single components and simple blends of components via EAG bioassay. The method utilizes two excised antennae placed across a "fork" electrode holder. The protocol demonstrated here presents a rapid, high-throughput standardized method for screening volatiles. Each volatile is at a set, constant amount as to standardize the stimulus level and thus allow antennal responses to be indicative of the relative chemoreceptivity. The negative control helps eliminate the electrophysiological response to both residual solvent and mechanical force of the puff. The positive control (in this instance acetophenone) is a single compound that has elicited a consistent response from male and female navel orangeworm (NOW) moth. An additional semiochemical standard that provides consistent response and is used for bioassay studies with the male NOW moth is (Z,Z)-11,13-hexdecadienal, an aldehyde component from the female-produced sex pheromone.     

Herbivore-induced plant volatiles mediate host selection by a root herbivore

In response to herbivore attack, plants mobilize chemical defenses and release distinct bouquets of volatiles. Aboveground herbivores are known to use changes in leaf volatile patterns to make foraging decisions, but it remains unclear whether belowground herbivores also use volatiles to select suitable host plants. We therefore investigated how above- and belowground infestation affects the performance of the root feeder Diabrotica virgifera virgifera, and whether the larvae of this specialized beetle are able to use volatile cues to assess from a distance whether a potential host plant is already under herbivore attack. Diabrotica virgifera larvae showed stronger growth on roots previously attacked by conspecific larvae, but performed more poorly on roots of plants whose leaves had been attacked by larvae of the moth Spodoptera littoralis. Fittingly, D. virgifera larvae were attracted to plants that were infested with conspecifics, whereas they avoided plants that were attacked by S. littoralis. We identified (E)-β-caryophyllene, which is induced by D. virgifera, and ethylene, which is suppressed by S. littoralis, as two signals used by D. virgifera larvae to locate plants that are most suitable for their development. Our study demonstrates that soil-dwelling insects can use herbivore-induced changes in root volatile emissions to identify suitable host plants.     

Odour masking of tomato volatiles by coriander volatiles in host plant selection of Bemisia tabaci biotype B

The silverleaf whitefly, Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae), is one of the most important pest insects in tomato crop systems worldwide. It has been previously demonstrated that intercropping tomato [Solanum lycopersicum L. Mill. (Solanaceae)] with coriander [Coriandrum sativum L. (Apiaceae)] reduces the incidence and severity of damage caused by B. tabaci. However, it is not yet known how coriander affects the insect′s behaviour. We evaluated the attractiveness of tomato constitutive volatiles to B. tabaci and what effect coriander constitutive volatiles have on the insect′s behaviour. To this end, we conducted three bioassays in a multiple‐choice four‐arm olfactometer (‘×’ type), measuring B. tabaci behaviour when offered tomato and coriander constitutive volatiles presented alone as well as together. We also evaluated the colonisation and establishment of B. tabaci in experimental plots with only single tomato plants and tomatoes intercropped with coriander in a greenhouse. Bemisia tabaci males and females recognised tomato constitutive volatiles as a positive stimulus (kairomonal effect), indicating that semiochemicals from this plant can play an important role in the insect’s host plant selection. Coriander constitutive volatiles reduced the attractiveness of tomato volatiles but no repellency to these volatiles was observed. Greater numbers of adults and nymphs of B. tabaci per plant were observed in tomato monoculture plots than in tomato intercropped with coriander. We suggest that coriander constitutive volatiles have an odour masking effect on tomato volatiles, thus interfering in the host plant selection of B. tabaci.     

Electrophysiological response to herbivore-induced host plant volatiles in the moth Spodoptera littoralis

In cotton, Gossypium hirsutum (Malvacae), the volatiles emitted from the plant change in response to herbivory. Ovipositing females of the Egyptian cotton leaf worm, Spodoptera littoralis (Boisd.) (Lepidoptera: Noctuidae) can discriminate between cotton plants subjected to larval feeding and undamaged plants during oviposition. In this study we investigate whether females of this moth can detect the herbivore-induced cotton volatiles. The response of female S. littoralis antennae to volatiles collected from cotton plants subjected to larval feeding was studied using GC-EAD (coupled gas chromatography electroantennographic-detection). By GC-EAD, responses to over 10 different cotton volatiles were observed. Using single sensillum technique the responses of short sensilla trichodea on the antennae of S. littoralis females to 19 cotton volatiles and 12 general plant volatiles were investigated. Responses to these volatiles were recorded from 108 receptor neurones. Several neurones activated by herbivore-induced cotton volatiles were recorded. For example, a neurone type responding to two homoterpenes [(E,E)-4,8,12-trimethyl-1,3,7,11-tridecatetraene and (E)-4,8-dimethyl-1,3,7-nonatriene] and (E,E)-α-farnesene was frequently found. We also observed sensitive neurones responding specifically to the herbivore-induced volatiles (+/–)-linalool and indole. In general, a stimulus load of less than 1 ng was needed to activate these neurones. In addition, specific neurones were found for constitutive cotton volatiles released in connection with damage to the plant. An abundant neurone type responded to β-caryophyllene and α-humulene. Another neurone type responded specifically to the non-induced cotton volatile (Z)-jasmone. These results show that females of S. littoralis have receptor neurones that would make it possible to discriminate between damaged and undamaged plants using volatile signals.     

Guava leaf volatiles and dimethyl disulphide inhibit response of Diaphorina citri Kuwayama to host plant volatiles

The Asian citrus psyllid, Diaphorina citri Kuwayama, vectors the causal pathogen of huanglongbing (HLB), which is likely the most important disease affecting worldwide citrus production. Interplanting citrus with guava, Psidium guajava L., was reported to reduce D. citri populations and incidence of HLB. We describe a series of investigations on the response of D. citri to citrus volatiles with and without guava leaf volatiles and to synthetic dimethyl disulphide (DMDS), in laboratory olfactometers and in the field. Volatiles from guava leaves significantly inhibited attraction of D. citri to normally attractive host‐plant (citrus) volatiles. A similar level of inhibition was recorded when synthetic DMDS was co‐released with volatiles from citrus leaves. In addition, the volatile mixture emanating from a combination of intact citrus and intact guava leaves induced a knock‐down effect on adult D. citri. Compounds similar to DMDS including dipropyl disulphide, ethyl‐1‐propyl disulphide, and diethyl disulphide did not affect the behavioural response of D. citri to attractive citrus host plant volatiles. Head‐space volatile analyses were conducted to compare sulphur volatile profiles of citrus and guava, used in our behavioural assays, with a gas chromatography‐pulsed flame photometric detector. DMDS, produced by wounded guava in our olfactometer assays, was not produced by similarly wounded citrus. The airborne concentration of DMDS that induced the behavioural effect in the 4‐choice olfactometer was 107 pg/ml. In a small plot field experiment, populations of D. citri were significantly reduced by deployment of synthetic DMDS from polyethylene vials compared with untreated control plots. Our results verify that guava leaf volatiles inhibit the response of D. citri to citrus host plant volatiles and suggest that the induced compound, DMDS, may be partially responsible for this effect. Also, we show that field deployment of DMDS reduces densities of D. citri and thus may have potential as a novel control strategy.     

植物挥发性物质在蚜虫寄主定位中的作用

本文综述了植物挥发性物质的化学性质、研究方法及其在蚜虫寄主定位中的作用     

Evolutionary changes in an invasive plant support the defensive role of plant volatiles

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Anthocorid predators learn to associate herbivore-induced plant volatiles with presence or absence of prey

We investigated how the plant‐inhabiting, anthocorid predator, Anthocoris nemoralis, copes with variation in prey, host plant and associated herbivore‐induced plant volatiles and in particular whether the preference for these plant odours is innate or acquired. We found a marked difference between the olfactory response of orchard‐caught predators and that of their first generation reared on flour moth eggs in the laboratory, i.e. under conditions free of herbivory‐induced volatiles. Whereas the orchard‐caught predators preferred odour from psyllid‐infested pear leaves, when offered against clean air in a Y‐tube olfactometer, the laboratory‐reared first generation of (naive) predators did not. The same difference was found when a single component (methyl salicylate) of the herbivore‐induced plant volatiles was offered against clean air. After experiencing methyl salicylate with prey, however, the laboratory‐reared predators showed a pronounced preference for this volatile. This acquired preference did not depend on whether the volatile had been experienced in the juvenile period or in the adult phase, but it did depend on whether it had been offered in presence or absence of prey. In the first case, they were attracted to the plant volatile in subsequent olfactometer experiments, but when the volatile had been offered during a period of prey deprivation, the predators were not attracted. We conclude that associative learning is the most likely mechanism underlying acquired odour preference.     

Non-consumptive effects of predatory mites on thrips and its host plant

Recent reviews on trait-mediated interactions in food webs suggest that trait-mediated effects are as important in triggering top–down trophic cascades as are density-mediated effects. Trait-mediated interactions between predator and prey result from non-consumptive predator effects changing behavioural and/or life history traits of prey. However, in biological control the occurrence of trait-mediated interactions between predators, prey and plants has been largely ignored. Here, we show that non-consumptive predator effects on prey cascade down to the plant in an agro-ecological food chain. The study system consisted of the predatory mites P. persimilis and N. californicus , the herbivorous non-target prey western flower thrips F. occidentalis and the host plant bean. Irrespective of predator species and risk posed to prey, the presence of predator eggs led to increased ambulation, increased mortality and decreased oviposition of thrips. Furthermore, the presence of predator eggs reduced leaf damage caused by thrips. To our knowledge this is the first experimental evidence suggesting a positive trophic cascade triggered by non-consumptive predator effects on non-target prey in an augmentative biological control system.     

寄主植物信息化合物对苹果蠹蛾行为的影响及其在防控中的应用

苹果蠹蛾（Cydia pomonella)是仁果类水果的重要世界性害虫,也是我国的重要检疫性对象,在我国的发生、危害及潜在扩张的趋势十分严峻.有关寄主植物气味对苹果蠹蛾特异性引诱方面的研究受到了广泛的关注.本文综述了苹果蠹蛾和植物源气味之间的互作关系,主要包括寄主植物气味影响苹果蠹蛾成虫寄主定位、求偶交配和产卵等行为,幼虫取食对寄主植物气味释放以及寄主植物气味对性信息素的影响;同时还介绍了主要植物源化合物梨酯的研究和田间应用概况,以期为我国苹果蠹蛾的防控研究和应用提供参考.     

Role of plant volatiles in host plant location of the leafminer, Liriomyza sativae (Diptera: Agromyzidae)

Abstract The role of plant volatiles in host plant location of the leafminer Liriomyza sativae Blanchard was studied. Four types of antennal sensilla were identified on the funiculus by scanning electron microscopy: trichoid, basiconic, clavate and grooved sensilla. An olfactory pit, containing groups of sensilla, was present on the ventral side of the funiculus. No sexual difference was detected in sensilla diversity and distribution. In behavioural assays, both males and females were attracted by the odour of the bean Phaseolus vulgaris L. They had distinct EAG responses to the bean odour. No significant sexual difference was found in behaviour or EAG responses.
Electroantennograms were recorded from female L. sativae to 14 plant volatile compounds. The most distinct EAG responses were obtained for: (1) the general green leaf volatiles 1-hexanol (E)-2-hexen-1-ol, (E)-3-hexen-1-ol and its isomers, (Z)-3-hexen-1-ol, the acetate (E)-3-hexenylacetate and the aldehyde hexanal; and (2) limonene, a compound associated with tomato, which is a key host plant of this insect. Other volatile compounds associated with host plants, such as α-pinene, myrcene, β-caryophyllene, and eugenol did not elicit responses. The ability of this insect to locate a host plant appears to be augmented by the perception of a combination of host-specific and general green leaf volatiles. A modification of the EAG recording method of Dipteran species was provided.     

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。     

白星花金龟对寄主植物挥发物的电生理反应

[目的]白星花金龟Protaetia brevitarsis是我国经济上重要的农业害虫.本研究拟鉴定苹果、葡萄和玉米3种果实在两种状态(健康与受白星花金龟成虫为害)下的挥发物中能引起白星花金龟雌成虫触角电生理反应的挥发物成分.[方法]采用动态顶空吸附法收集苹果、葡萄和玉米3种果实的挥发物,用气相色谱-触角电位联用技术(...     

Plant volatiles mediate attraction to host and non-host plant in apple fruit moth, Argyresthia conjugella

Plant volatiles mediate host finding in insect herbivores and lead to host fidelity and habitat‐specific mating, generating premating reproductive isolation and facilitating sympatric divergence. The apple fruit moth, Argyresthia conjugella Zeller (Lepidoptera: Argyresthiidae), is a particularly suitable species to study the cues and behavioural mechanisms leading to colonization of a new host: it recurrently oviposits on the non‐host plant, apple Malus domestica Borkh. (Rosaceae), where the larvae cannot complete their development. The larval host of the apple fruit moth (Lepidoptera, Argyresthiidae), is rowan Sorbus aucuparia L. (Rosaceae). Fruit setting in rowan, however, fluctuates strongly over large areas in Scandinavia. Every 2–4 years, when too few rowanberries are available for egg laying in forests, apple fruit moth females oviposit instead on apple in nearby orchards, but not on other fruits, such as pear or plum. This poses the question of which cues mediate attraction to rowan and apple, and how apple fruit moth discriminates rowan from apple. Chemical analysis and antennal recordings showed that 11 out of 15 rowan volatiles eliciting an antennal response in A. conjugella females co‐occur in rowan and apple headspace, in a different proportion. In the field, A. conjugella was attracted to several of these plant volatiles, especially to 2‐phenyl ethanol, methyl salicylate, and decanal. Addition of anethole to 2‐phenyl ethanol had a strong synergistic effect, the 1 : 1 blend is a powerful attractant for A. conjugella males and females. These results confirm that volatiles common to both plants may account for a host switch in A. conjugella from rowan to apple. Some of the most attractive compounds, including 2‐phenyl ethanol, anethole, and decanal, which have been found in several apple cultivars, were not present in the headspace of the apple cultivar, Aroma, which is also susceptible to attack by A. conjugella. This supports the idea that the odour signal from apple is suboptimal for attraction of A. conjugella, but is nonetheless sufficient for attraction, during times when rowan is not available for egg laying.     

Discrepancy in laboratory and field attraction of apple fruit moth Argyresthia conjugella to host plant volatiles

Abstract.  Apple fruit moth Argyresthia conjugella is a specialist seed predator of rowan Sorbus aucuparia . Large-scale synchronous fluctuation of seed production in rowan (i.e. named masting) drives the apple fruit moth to seek alternative host plants such as apple, during years when rowan berries are not available for oviposition. The role of plant volatile compounds in the attraction of gravid apple fruit moth females is studied in a laboratory wind tunnel. Volatiles from rowan branches with green berries stimulate female moths to fly upwind and to land at the odour source. By contrast, females are not attracted to rowan branches without green berries, and they are not attracted to apple, demonstrating that the chemical stimulus from rowan berries is required for attraction. Attraction to synthetic compounds identified from rowan, anethole and 2-phenyl ethanol confirms the role of plant volatiles in host finding. These two compounds, however, show a discrepant behavioural effect in wind tunnel and field tests. Field traps baited with 2-phenyl ethanol capture female moths but anethole does not produce significant captures. Wind tunnel tests produce the opposite results: moths fly upwind towards the anethole lure, whereas 2-phenyl ethanol is not attractive at all. Wind tunnel attraction to 2-phenyl ethanol is achieved by adding odour from a rowan branch without berries, which is not attractive on its own. This finding demonstrates that interaction with the background odour contributes to the behavioural effect of plant volatile stimuli in the field.     

Antennal and behavioural responses of Heortia vitessoides females to host plant volatiles of Aquilaria sinensis

This study investigated volatiles from Aquilaria sinensis (Lour.) Gilg (Thymelaeaceae) leaves that attracted Heortia vitessoides Moore (Lepidoptera: Crambidae). Volatiles from young and old A. sinensis leaves were identified and quantified by gas chromatography–mass spectrometry and gas chromatography‐electroantennogram detection. Both wind tunnel bioassays and field tests were conducted to measure the attraction of adults to synthetic blends of volatiles from leaves of different maturations. Consistent electroantennographic activity was obtained for nine and three compounds from headspace collections of young and old A. sinensis leaves, respectively. Qualitative and quantitative differences were found among two odour profiles. In wind tunnel experiments, the fresh young leaves proved to be more attractive to females than old leaves. A nine‐component mixture, including hexanal, limonene, 2‐hexanol, octanal, (Z)‐3‐hexenyl acetate, (Z)‐3‐hexen‐1‐ol, nonanal, decanal, and 2,6,10‐trimethyl‐dodecane (with a ratio of 2:16:9:4:63:100:13:10:5) from young leaves attracted moths significantly more than the three‐component mixture of nonanal, decanal, and 2,6,10‐trimethyl‐dodecane (with a ratio of 11:14:26) from old leaves. Further subtractive bioassays conducted in the wind tunnel showed that both the complete nine‐component mixture and a subtracted four‐component mixture of hexanal, (Z)‐3‐hexenyl acetate, nonanal, and decanal (with a ratio of 2:63:13:10) elicited equivalent responses in females. All components in the four‐component blend were essential for optimal attraction. In a field trial using the nine‐ and four‐component blends, more moths were captured using both blends than in traps baited with hexane only. Our study indicates that the odour blends of young leaves play an important role in H. vitessoides host plant recognition. The mechanisms behind host recognition and age‐dependent changes in leaf chemistry are discussed.     

Antennal olfactory sensory neurones responsive to host and nonhost plant volatiles in gorse pod moth Cydia succedana

We investigate the response profiles of the antennal olfactory sensory neurones (OSNs) in male and female gorse pod moth Cydia succedana to host and nonhost volatiles, using the single sensillum recording technique. Eight different classes of olfactory sensilla are identified in female C. succedana and five different classes of olfactory sensilla in males. Nineteen different classes of OSNs are identified from the sensilla in females, and nine different classes of OSNs in the male sensilla. All classes of sensilla, except class F7 and class M1 sensilla, co‐compartmentalize two or three OSNs in each sensillum, and the OSNs present in the same sensillum are specialized for different volatiles. Most plant‐volatile OSNs exhibit phasic‐tonic type of temporal responses, whereas the pheromone OSNs in male C. succedana show rather phasic responses. The majority of OSNs identified in C. succedana display highly specialized responses to a narrow range of volatiles, whereas only a small proportion of OSNs show broad response spectra. Two most abundant classes of OSNs exhibit highly specialized responses to β‐myrcene and (E)‐β‐ocimene, two major volatiles released by gorse (Ulex europaeus), the main host of C. succedana. By contrast, several other classes of OSNs exhibit highly specialized responses to geraniol, (Z)‐3‐hexen‐1‐ol, (±)‐α‐terpineol, citral and benzyl acetate, which are produced by various nonhost plants. Taking the results of the present study together, we suggest that C. succedana use the combinational input from a set of highly specialized OSNs for host plant volatiles and another set of highly specialized OSNs for nonhost volatiles to discriminate between hosts and nonhosts.