Host recognition by Rhinocyllus conicus of floral scents from invasive and threatened thistles

One of the main obstacles of classical biological control is that biological control organisms cannot be recalled once they are released in nature. It is particularly true for the flowerhead weevil, Rhinocyllus conicus Frölich, which was released as a biological control organism for the invasive musk thistle, Carduus nutans L. (MT). While weevils successfully suppressed introduced populations of musk thistles and other invasive thistle species, non-target attacks have been reported on multiple native thistles including federally listed threatened and endangered (T&E) thistle species. To investigate the foraging behavior of female weevils on invasive and native thistles, we examined volatile organic compounds (VOCs) emitted from MT and a T&E plant species, Sacramento Mountains thistle, Cirsium vinaceum Wooton & Standley (SMT) in the Lincoln National Forest, New Mexico. We used a dynamic headspace volatile collection system and gas chromatography-mass spectrometry to compare volatile profiles between MT and SMT. Female weevils reacted to 7 electrophysiologically active chemical compounds in the blends based on gas chromatography-electroantennography. The behavioral response of female weevils was indifferent when VOCs from both thistles were offered in y-tube olfactometry experiments. Yet, they preferred VOCs collected from MT to purified air. The searching time of female weevils was longer to VOCs collected from SMT over controls. Investigating signals during the initial host recognition of released biological control organisms may open new opportunities to reduce non-target attacks on T&E plant species.

     

Olfactory responses of Aethina tumida murray (Coleoptera: Nitidulidae) to some major volatile compounds from hive materials and workers of Apis mellifera

The small hive beetle (Aethina tumida Murray) is an invasive pest affecting honey bee colonies. The beetles are known to be attracted to volatiles from hive products and honey bees like Apis mellifera L. Previously we reported the presence of five major compounds from the volatile extracts of hive materials; ethyl linolenate and ethyl palmitate from pollen dough, oleamide and tetracosane in fermenting honey, and oleamide and 5-methyl-2-phenyl-1H-indole from A. mellifera worker bees. This study tested the attractiveness of the aforementioned five volatile organic compounds to small hive beetles (SHB) by Y-tube olfactometric bioassay. Ethyl linolenate was highly attractive to both male and female adults of SHB. Ethyl palmitate was attractive to SHB only at higher concentration (0.01–01 mg/ml). Interestingly, tetracosane, 5-methyl-2-phenyl-1H-indole and oleamide were repellent for SHB of both sexes, but ethyl linolenate and ethyl palmitate as components of honey bee brood pheromone attracted SHB. The results highlight that SHB differentially utilizes volatile chemicals from hive materials and honey bees as cues to locate honey bee hives.     

Differences in volatile emissions between healthy and gall-induced branches of Haplopappus foliosus (Asteraceae)

Changes in plant secondary metabolism due to insect galls are one of the frontiers in knowledge of plant-insect interactions, especially concerning volatile organic compounds (VOCs). Here we studied the in vivo VOCs released from healthy apical branches of Haplopappus foliosus DC. (Asteraceae) and compared these volatiles to the VOCs obtained from apical bud galls produced in this host plant when attacked by the gall midge Haplopappusmyiia gregaria (Cecidomyiidae). We field-collected VOCs by dynamic headspace and identified them by gas chromatography coupled to mass spectrometry. We found changes in the relative proportions of different classes of VOC in apical branches vs. apical bud galls. H. foliosus VOCs had mainly monoterpene hydrocarbons such as p-cymene, a recognized herbivore deterrent. We also found oxygenated monoterpenes and sesquiterpenes in the H. foliosus volatile mixture. H. foliosus modifies its fragrance composition when parasitized by gall midges, showing an increased proportion of some monoterpene hydrocarbons, e.g. limonene and camphene, while others such as α-thujene, p-cymene and γ-terpinene were down-expressed in apical bud gall VOCs. We discuss these results considering gall signaling and chemical ecology hypotheses, including the potential role of plant defenses as well as gall midge-derived modification for host plant VOCs, and comment on the ecological relevance of our findings.     

Electrophysiological and behavioral response of the oriental fruit moth <Emphasis Type="Italic">Grapholita</Emphasis><Emphasis Type="Italic">molesta</Emphasis> (Busck, 1916) (Lepidoptera: Tortricidae) to the volatiles of apple fruits at different stages of development

The oriental fruit moth, Grapholita molesta, occurs in Southern Brazil throughout the year, and migrates from peach to apple orchards. Because moths rely on volatile organic compounds (VOCs) during the host-location process, variations in the emission of these compounds during fruit maturation can influence the time of infestation and preference of the moths for a particular genotype. The aim of this work was to identify VOCs emitted by the apples “Eva” and “Gala” at different stages of development and to determine the behavioral and electrophysiological responses of G. molesta to these compounds. For this purpose, VOCs from immature, maturing, and mature fruits of both cultivars were collected and analyzed by gas chromatography and gas chromatography-mass spectroscopy. The response of the antennae of virgin males and females and mated females to volatiles released by the three fruit stages was registered by gas chromatography coupled to an electroantennography. A dual-choice behavioral test for the different combinations of insect groups and fruit stage was also performed. Amongst the volatiles released by mature fruits, twelve compounds elicited a response. The antennae of the oriental fruit moth did respond to isoamyl hexanoate and α-farnesene emitted by “Eva” maturing fruits. In general, virgin females did not respond to volatiles in olfactometer bioassays and mated females were attracted to volatiles released by mature fruits. Our results show that the variation in the emission during the maturation of fruits can influence the orientation of G. molesta.     

Nematicidal effect of volatiles produced by Trichoderma sp.

Trichoderma is an important biocontrol agent that produces metabolites harmful to nematodes. We investigated the volatile organic compounds (VOCs) of Trichoderma sp. YMF 1.00416 and examined their abilities to kill nematodes. Chemical investigations of the VOCs from this strain led to the isolation and identification of three metabolites: a new compound, 1β-vinylcyclopentane-1α,3α-diol (1) and two known metabolites, 6-pentyl-2H-pyran-2-one (2) and 4-(2-hydroxyethyl)phenol (3). Nematicidal activity assays showed that compound 2 was nematicidal, and killed > 85% of Panagrellus redivivus, Caenorhabditis elegans, and Bursaphelenchus xylophilus in 48 h at 200 mg/L in a 2 mL vial. Our results will help identify new nematicides.     

Mountain Pine Beetles Use Volatile Cues to Locate Host Limber Pine and Avoid Non-Host Great Basin Bristlecone Pine

The tree-killing mountain pine beetle (Dendroctonus ponderosae Hopkins) is an important disturbance agent of western North American forests and recent outbreaks have affected tens of millions of hectares of trees. Most western North American pines (Pinus spp.) are hosts and are successfully attacked by mountain pine beetles whereas a handful of pine species are not suitable hosts and are rarely attacked. How pioneering females locate host trees is not well understood, with prevailing theory involving random landings and/or visual cues. Here we show that female mountain pine beetles orient toward volatile organic compounds (VOCs) from host limber pine (Pinus flexilis James) and away from VOCs of non-host Great Basin bristlecone pine (Pinus longaeva Bailey) in a Y-tube olfactometer. When presented with VOCs of both trees, females overwhelmingly choose limber pine over Great Basin bristlecone pine. Analysis of VOCs collected from co-occurring limber and Great Basin bristlecone pine trees revealed only a few quantitative differences. Noticeable differences included the monoterpenes 3-carene and D-limonene which were produced in greater amounts by host limber pine. We found no evidence that 3-carene is important for beetles when selecting trees, it was not attractive alone and its addition to Great Basin bristlecone pine VOCs did not alter female selection. However, addition of D-limonene to Great Basin bristlecone pine VOCs disrupted the ability of beetles to distinguish between tree species. When presented alone, D-limonene did not affect behavior, suggesting that the response is mediated by multiple compounds. A better understanding of host selection by mountain pine beetles could improve strategies for managing this important forest insect. Moreover, elucidating how Great Basin bristlecone pine escapes attack by mountain pine beetles could provide insight into mechanisms underlying the incredible longevity of this tree species.     

Epirrita autumnata induced VOC emission of silver birch differ from emission induced by leaf fungal pathogen

The production of volatile organic compounds (VOCs) through the activation of different signal-transduction pathways may be induced in various biotic and abiotic stress situations having importance e.g. in insect and disease resistance. We compared the emission of VOCs emitted from silver birch Betula pendula Roth (clones 4 and 80) twigs damaged either by larvae of Epirrita autumnata, or infected with pathogenic leaf spot causing fungus Marssonina betulae. We also analysed whether local herbivore damage can systemically induce the release of VOCs from the undamaged top of same sapling. The emissions of methylsalicylate (MeSA), (Z)-ocimene, (E)-β-ocimene, (E)-4,8-dimethyl-1,3,7-nonatriene (DMNT) and linalool were induced from the twigs after 72 h feeding damage by E. autumnata larvae. However, 48 h feeding damage did not induce rapid systemic release of VOCs from undamaged top leaves of the same twigs. Pathogen-infected birch twigs had significantly greater emission of (Z)-ocimene and (E)-β-ocimene than intact control twigs. The emission of DMNT was not significantly induced and MeSA was not found at all after pathogen infection, both being significantly different from herbivore damaged twigs. According to our results leaf fungal pathogen induces VOC emission profile differs from that of arthropod herbivore-damaged leaves, suggesting that birch is able to transmit parasite-specific information via VOC emissions to conspecifics and natural enemies of herbivores. Handling editor: Yvan Rahbé     

桑天牛卵长尾啮小蜂的寄主选择定位行为

本文对桑天牛卵长尾啮小蜂Aprostocetus prolixus LaSalle et Huang的寄主选择定位行为进行了系统研究。已有研究表明,寄主植物-寄主昆虫复合体释放的挥发物对寄生蜂有显著的引诱作用。为了查明寄主植物 寄主昆虫复合体中挥发性引诱物质的来源,对不同处理桑枝（正常桑枝、机械损伤桑枝、系统枝、桑天牛Apriona germari（Hope）咬食和产卵桑枝）、桑天牛虫粪及雌雄两性桑天牛所释放的挥发物分别进行了测定。结果显示：不同处理桑枝对寄生蜂都具有显著的引诱作用,而且产卵桑枝的引诱活性最大;桑天牛虫粪的气味对寄生蜂有引诱活性,而雌、雄桑天牛体表挥发物对寄生蜂的引诱效果不明显。桑天牛爬行痕迹对寄生蜂的微栖境接受行为没有影响,而桑天牛虫粪中的信息物质在寄生蜂的微栖境接受过程中起着重要作用。寄生蜂对产卵桑枝段的选择几率明显高于正常桑枝段和咬食桑枝段,而对不同植物上产卵刻槽的选择没有差异; 刻槽表面存在着与此卵寄生蜂寄主识别相关的信息物质。     

Pinus koraiensis twigs affect Monochamus saltuarius (Coleoptera: Cerambycidae) longevity and reproduction

This study was conducted to investigate the longevity, reproduction and ovarian development of M. saltuarius adults feeding on Pinus koraiensis twigs of three different age classes (current-year, 1-year and 2-year). Longevity and fecundity of female adults decreased with increasing twig age class (58.4, 41.9 and 35.9 days, respectively, for longevity and 43.0, 13.2 and 6.6 eggs, respectively, for fecundity). In ovarian development, the average follicle size after 1 week of feeding on current-year twigs was 3.1–3.5 times greater than those of beetles fed 1- and 2-year-old twigs. After 2 weeks of feeding, follicle size was 2.3–2.4 times greater than those of beetles fed 1- and 2-year-old twigs. These results showed that current-year twigs of P. koraiensis increase longevity and reproduction of M. saltuarius. By analyzing sugars using high performance liquid chromatography (HPLC), the quantity of fructose was found to be highest in current-year twigs and lowest in 2-year-old twigs. A sugar feeding bioassay indicated that fructose was preferred by M. saltuarius. Therefore, fructose is important to adult feeding and ovariole development in M. saltuarius.     

Tannin allocation in blackbrush (Coleogyne ramosissima)

Blackbrush (Coleogyne ramosissima) is a spinescent shrub occurring in nearly monospecific stands in the southwestern United States. Winter browsing by domestic goats stimulates spring twig production by blackbrush plants. Current season's twigs produced by older branches growing on the outer edges of the plant canopy (terminal branches) contained 2.37 times more tannins than did older twigs. Within blackbrush plants, current season's twigs on terminal branches contained 1.34 times more tannins than did current season's twigs on sprouts and younger branches (basal branches). When analysed separately, current season's terminal twigs contained 1.47 times more tannins than did leaves, while current season's basal twigs contained 1.10 times more tannins than did leaves. Phytochemicals, mainly phenolics, in blackbrush reduce its risk of being over-utilized by domestic herbivores, and the occurrence and distribution of tannins in blackbrush lend support to hypotheses dealing with secondary compounds as plant defences.     

One shot-two pathogens blocked: Exposure of Arabidopsis to hexadecane,a long chain volatile organic compound,confers induced resistance against both Pectobacterium carotovorum and Pseudomonas syringae

Bacteria and plant derived volatile organic compounds have been reported as the chemical triggers that elicit induced resistance in plants. Previously, volatile organic compounds (VOCs), including acetoin and 2,3-butanediol, were found to be emitted from plant growth-promoting rhizobacteria (PGPR) Bacillus subtilis GB03, which had been shown to elicit ISR and plant growth promotion. More recently, we reported data that stronger induced resistance could be elicited against Pseudomonas syringae pv maculicola ES4326 in plants exposed to C13 VOC from another PGPR Paenibacillus polymyxa E681 compared with that of strain GB03. Here, we assessed whether another long hydrocarbon C16 hexadecane (HD) conferred protection to Arabidopsis from infection of a biotrophic pathogen, P. syringae pv maculicola and a necrotrophic pathogen, Pectobacterium carotovorum subsp carotovorum. Collectively, long-chain VOCs can be linked to a plant resistance activator for protecting plants against both biotrophic and necrotrophic pathogens at the same time.     

Two new antioxidant flavones from the twigs of Eriosema robustum (Fabaceae)

Phytochemical study of the ethanol extract of the twigs of Eriosema robustum, a Cameroonian medicinal plant resulted to the isolation of two new flavones, 2′,3′,5′,5,7-pentahydroxy-3,4′-dimethoxyflavone (1) and 2′,3,5′,5,7-pentahydroxy-4′-methoxyflavone (2), along with five known compounds: 6-prenylpinocembrin (3), 1-O-heptatriacontanoyl glycerol (4), β-sitosterol (5), stigmasterol (6) and 3-O-β-d-glucopyranoside of sitosterol (7). The structure of the isolated compounds were elucidated on the basis of their NMR, UV and MS data, and by comparison with those reported in the literature. The ethanol crude extract, fractions and some isolated compounds (1–4) were evaluated for their radical scavenging capacity using 2,2-diphenyl-1-picryhydrazyl (DPPH). The crude extract, fraction II, the new compounds namely robusflavones A (1) and B (2) exhibited significant antioxidant activity.     

Discriminant analysis of volatile organic compounds of Fusarium oxysporum f. sp. cepae and Fusarium proliferatum isolates from onions as indicators of fungal growth

Basal rot is a common onion disease and is mainly caused by Fusarium oxysporum f. sp. cepae and Fusarium proliferatum. To study the possibility of using volatile organic compounds (VOCs) as biomarkers for these fungi, pathogenic isolates of F. oxysporum and F. proliferatum from onions were cultivated in onion medium and VOCs were measured by solid phase microextraction (SPME). Forty-two compounds were detected, and thirty of these compounds were highly related to fungal metabolic activity. Allyl mercaptan was specific to F. oxysporum isolate Fox006. Analysis of the VOCs showed significant differences between the two species and among different isolates within the same species. Sixteen of the VOCs showed were highly positively correlated with the fungal biomass estimated by real-time polymerase chain reaction (PCR). Ethanol, ethyl formate, ethyl acetate, 2-methyl-1-propanol, methyl thioacetate, n-propyl acetate and 3-methyl-1-butanol are volatile metabolites that were potential indicators of Fusarium growth on onions.     

Characterization of volatile organic compounds emitted by kiwifruit plants infected with <Emphasis Type="Italic">Pseudomonas syringae</Emphasis> pv. <Emphasis Type="Italic">actinidiae</Emphasis> and their effects on host defences

Key message

Specific VOC emissions from infected plants allow their recognition and elicit defence responses in neighboring plants, which are, however, insufficient to induce resistance.

Abstract

A wide range of volatile organic compounds (VOCs) is released during plant–pathogen interactions both by the pathogens and the hosts. Some of these VOCs are specific for the different diseases and are known to play a role in the pathogenicity or in plant defence responses. Besides, disease-specific VOCs may serve as markers for diagnostic protocols, which allow a non-destructive and rapid screening of bulk samples of plant material. This work aimed to verify the feasibility of a VOC-based diagnosis and to investigate the possible biological role of VOCs released during the plant–pathogen interactions. The volatile emissions from Pseudomonas syringae pv. actinidiae in axenic cultures and from inoculated in vitro kiwifruit plants were characterized by gas chromatography–mass spectrometry (GC–MS) and proton transfer reaction–time-of-flight-mass spectrometry (PTR–ToF-MS). By GC–MS, several putative biochemical markers, such as 1-undecene, were identified. PTR–ToF-MS resulted highly effective in screening the plant material for latent infections. To develop a more user-friendly, portable and less expensive diagnosis system, two different electronic nose models were tested for the early diagnosis of P. syringae pv. actinidiae in asymptomatic plant material. Our experiments demonstrated the feasibility of the electronic nose-based screening of infected plant material. Concerning the biological role of the VOCs released during the plant–pathogen interactions, the exposure of healthy plants to VOCs from infected ones influences the plant growth and induces the stimulation of protective responses. However, after the infection, P. syringae pv. actinidiae is able to selectively inactivate the induced plant defences.

     

The role of herbivory by wood-boring insects in mangrove ecosystems in Belize

The roles wood-boring insects play in modifying mangrove ecosystems were examined on small, offshore mangrove islands in Belize. Several species of xylem- and phloem-feeding woodborers consume the wood of living mangrove trees. By girdling, pruning, and hollowing, woodborers killed over 50% of the Rhizophora mangle canopy in experimental plots arrayed across a tidal-elevation gradient. In contrast, leaf-feeding herbivores removed less than 6% of the canopy. In the plots, stem girdlers killed over three branches per tree. The patterns of herbivory by three functional feeding groups were heterogeneous and did not vary consistently with tidal elevation. Because R. mangle lacks viable axillary buds or the ability to produce epicormic shoots to replace pruned branches, the canopy architecture was significantly modified by this damage. The branches that were pruned by stem girdlers created numerous small holes or gaps in the mangrove canopy. Shoot growth and flowering increased in R. mangle trees with 50% of their branches experimentally girdled. Because branches and twigs attacked by woodborers lost their leaves prematurely as greenfall, the quantity and quality of leaf litter were altered when a leaf-bearing branch was girdled or hollowed. These changes suggest that wood-boring insects also significantly affect internal and external nutrient cycling processes in mangrove ecosystems.     

Validation of analytical method for (E)-2-decenedioic acid quantification in honey samples

Natural honey is a highly sought-after product owing to its biological uniqueness. We developed a suitable analytical method for the quantitative analysis of (E)-2-decenedioic acid in Korean natural and sugar-fed honey samples. A total of 258 honey samples were screened using ultra-performance liquid chromatography (UPLC) for the detection and quantification of (E)-2-decenedioic acid. (E)-2-decenedioic acid was present in high concentrations (122–127 mg/kg) in sugar-fed honey but only in trace amounts (10.9–14.8 mg/kg) in natural honey. Findings indicate that the UPLC method is suitable and reliable for the quantitative evaluation of (E)-2-decenedioic acid in honey. We expect that this method will be applicable for detecting honey adulteration.     

Production of volatile organic compounds by an antagonistic strain Paenibacillus polymyxa WR-2 in the presence of root exudates and organic fertilizer and their antifungal activity against Fusarium oxysporum f. sp. niveum

The volatile organic compounds (VOCs) produced by antagonistic microbes have great antifungal potential against soil-borne fungal pathogens. The VOCs produced by Paenibacillus polymyxa strain WR-2 in the presence of root exudates and organic fertilizer were identified and their effects on the growth and spore germination of Fusarium oxysporum f. sp. niveum were evaluated. The VOCs produced by WR-2 inhibited the growth of F. oxysporum by 38%, 36% and 40% in agar medium, sterilized soil and natural soil, respectively. This inhibitory effect was increased to 60%, 58% and 64% with the addition of organic fertilizer in agar medium, sterilized soil and natural soil, respectively. The addition of root exudates did not affect the production of antifungal VOCs by WR-2. The VOCs produced by WR-2 completely inhibited the germination of F. oxysporum spores. Out of 42 identified VOCs, seven VOCs; benzothiazole, benzaldehyde, undecanal, dodecanal, hexadecanal, 2-tridecanone and phenol were found to inhibit the growth of F. oxysporum. The results of these experiments suggest another significance of using organic fertilizer as a carrier material with the biocontrol agents to control soil-borne fungal pathogens.     

Volatile organic compounds of some Trichoderma spp. increase growth and induce salt tolerance in Arabidopsis thaliana

Many beneficial effects of Trichoderma spp. on plant growth and/or resistance to biotic/abiotic stresses can result from the production of bioactive compounds including volatile organic compounds (VOCs). We evaluated the effects of the volatile mixtures from 13 strains of different Trichoderma species on induction of tolerance to salt stress (100 mM NaCl) as well as growth promotion of Arabidopsis thaliana. Plants responded differently due to the presence of VOCs from various Trichoderma species ranging from both growth promotion and induction of salt tolerance to no significant changes under any of the conditions tested. In plants exposed for 2 weeks to VOCs of the selected strain, i.e. Trichoderma koningii, there was less H₂O₂ accumulation under salt stress compared to that in control plants. This result may reflect the possible role of VOCs of this strain in plant protection against oxidative damage under salt stress. Together, induction of salt tolerance using VOCs should be added to the known mechanisms of plant vigor enhancement by Trichoderma spp.     

鞭角华扁叶蜂对自然生境柏木挥发物释放的影响

植物挥发物（Volatile organic compounds;VOCs）在植物抵御害虫侵袭的过程中具有重要作用。本研究以重庆市云阳县长江林场人工林中健康和受害柏木为研究对象,通过VOCs测定分析发现鞭角华扁叶蜂虫害发生之前,两种柏木共计有37种VOCs成分,主要为萜类化合物,其次为醇、酯、醛、烷烃等类化合物;其中健康柏木特有驱赶作用的2-莰醇（龙脑）,受害柏木特有吸引作用的顺式-2-癸烯醛,其余35种为共有成分;各成分浓度在两种柏木中存在较大差异。虫害发生之后,两种柏木共计有32种VOCs成分,而2-莰醇、顺式-2-癸烯醛、薄荷醇、臭樟脑和α-石竹烯等5种成分消失;许多成分的浓度变化趋势与虫害发生前的相反。结果表明健康与受害柏木VOCs释放的差异可能是柏木能否抵御鞭角华扁叶蜂侵害的主要防御机制之一,这将为优良抗虫柏木选育提供理论依据和参考指标。     

Effects of aphid herbivory on volatile organic compounds of Artemisia annua and Chrysanthemum morifolium

We showed the effect of aphid infesting on the volatile organic compounds (VOCs) emitted by the infested Artemisia annua and Chrysanthemum morifolium cultivar ‘Nan nong hong feng’ plants by using headspace solid-phase microextraction (HS-SPME) method combined with gas chromatography mass spectrometry (GC–MS). In olfactometer bioassay experiment, aphids showed a preference for the odour of both healthy and infested chrysanthemum, while we found an opposite result in A. annua. Aphids tend to healthy plants compared with the infested, and the phenomenon became obvious with time. Different extracts were tested with the healthy plants and aphid infested plants. Eucalyptol, β-caryophyllene, (E)-β-farnesene, and germacrene D were released as the major constituents in both species. After aphid infesting, we observed a great increase in artemisia ketone and (E)-β-farnesene and a decrease in germacrene D in A. annua; comparatively, eucalyptol, isoborneol and β-caryophyllene increased in chrysanthemum. Combined with the GC–MS data and olfactometer bioassay results we concluded that (E)-β-farnesene and artemisia ketone emitted from A. annua might act as a potential volatile compound to resist aphids, and the two compounds would be useful for future ecological control of aphid in chrysanthemum cultivation.