Volatiles released from cotton plants in response to<Emphasis Type="Italic"> Helicoverpa zea</Emphasis> feeding damage on cotton flower buds

Feeding of Helicoverpa zea larvae on cotton (Gossypium hirsutum L.) flower buds (squares) for 24 or 48 h induced the release of a number of terpenes [(E)--ocimene, linalool, (E)--farnesene, (E,E)--farnesene, (E)-4,8-dimethyl-1,3,7-nonatriene, (E,E)-4,8,12-trimethyl-1,3,7,11-tridecatetraene], isomeric hexenyl butyrates, 2-methylbutyrates, indole and (Z)-3-hexenyl acetate. These compounds are not released in significant amounts from undamaged squares and freshly damaged squares. The release of inducible compounds was not limited to the damaged squares themselves. The compounds were also released systemically from the upper undamaged leaves of the same plant after 72 h. However, the composition of the blend of systemically released volatiles differed from the blend released by damaged squares. The compounds that were systemically released from undamaged leaves in response to feeding on the squares were (Z)-3-hexenyl acetate, (E)--ocimene, linalool, (E)-4,8-dimethyl-1,3,7-nonatriene, (E)--farnesene, (E,E)--farnesene, and indole. This study shows that insect damage inflicted to the reproductive parts of a plant causes a systemic emission of volatiles from its vegetative parts.     

Systemic induction of volatile release in cotton: How specific is the signal to herbivory?

Plants attacked by herbivorous insects release chemical signals that attract natural enemies of the herbivores to the damaged plants. Feeding of Spodoptera exigua larvae on the lower leaves of cotton (Gossypium hirsutum L.) for multiple feeding periods of 9–12 h with a 12 h, interval in between when the caterpillars are removed overnight, will induce a systemic release of volatile compounds that is comparable to the volatiles released in response to continuous feeding damage on the lower leaves for several days. The systemic volatile release in response to herbivory can be mimicked by mechanically damaging the lower leaves and applying caterpillar oral secretion to the injured leaves over 4 days. Cotton plants that are only mechanically damaged systemically release significantly less -pinene, myrcene, (Z)-3-hexenyl acetate, (E)--farnesene and (E,E)--farnesene after 4 days compared to plants damaged mechanically with application of caterpillar regurgitant. However, multiple 9–12 h mechanical damage alone induces a significantly higher systemic release of (Z)-3-hexenyl acetate, myrcene, (E)--ocimene, and (E)--farnesene after 4 days compared to undamaged control plants. This indicates that multiple mechanical damage alone cannot mimic completely the response induced by mechanically injuring the leaves and applying caterpillar regurgitant. A specific elicitor in the regurgitant of the caterpillar enhances the amount of several systemically released volatiles. Thus, the systemic release of volatile compounds by herbivore-damaged cotton plants appears to be regulated by at least two different mechanisms.     

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     

Differential utilization of ash phloem by emerald ash borer larvae: ash species and larval stage effects

• 1 Two experiments were performed to determine the extent to which ash species (black, green and white) and larval developmental stage (second, third and fourth instar) affect the efficiency of phloem amino acid utilization by emerald ash borer (EAB) Agrilus planipennis Fairmaire (Coleoptera: Buprestidae) larvae.
• 2 EAB larvae generally utilized green ash amino acids more efficiently than those of the other two species. For example, the concentrations of only six (two essential) and seven (two essential) amino acids were lower in frass from EAB that fed upon black and white ash than in the corresponding phloem, respectively. By contrast, concentrations of 16 (eight essential) amino acids were lower in the frass from EAB that fed upon green ash than in the phloem. In addition, in green ash, the frass : phloem ratios of 13 amino acids were lower than their counterparts in black and white ash.
• 3 The concentrations of non‐essential amino acids glycine and hydroxylproline were greater in frass than in phloem when EAB fed on black ash, although not when EAB fed on green or white ash.
• 4 The concentration of total phenolics (a group of putative defensive compounds to EAB, expressed as antioxidant activity of acetone extraction) was high in EAB frass but even higher in the phloem samples when the data were pooled across ash species and EAB larval stages. This suggests EAB larvae may eliminate phenolics through a combination of direct excretion and enzymatic conversion of phenolics to nonphenolics before excretion. Because the ratio of frass total phenolics to phloem total phenolics in white ash was lower than the ratios in black and green ash, the ability to destroy phenolics or convert them to nonphenolics was greater when EAB larvae fed on white ash.
• 5 Fourth‐instar EAB extracted phloem amino acids, including threonine, more efficiently than third‐instar EAB. The different larval developmental stages of EAB did not differ in their apparent ability to destroy phenolics or convert them to nonphenolics.

     

Abundance of volatile organic compounds in white ash phloem and emerald ash borer larval frass does not attract Tetrastichus planipennisi in a Y‐tube olfactometer

Many natural enemies employ plant‐ and/or herbivore‐derived signals for host/prey location. The larval parasitoid Tetrastichus planipennisi Yang (Hymenoptera: Eulophidae) is 1 of 3 biocontrol agents currently being released in an effort to control the emerald ash borer (EAB), Agrilus planipennis Fairmaire (Coloeptera: Burprestidae) in North America. To enhance its efficiency, allelochemicals that attract it need to be assessed. In this study, ash phloem volatile organic compounds (VOCs) of black, green, and white ash, and EAB larval frass were compared. Foraging behavior of T. planipennisi females in response to VOCs of white ash or frass from EAB larvae feeding on white ash phloem was tested using a Y‐tube olfactometer. Results indicated that the 3 ash species had similar VOC profiles. EAB larval frass generally contained greater levels of VOCs than phloem. Factor analysis indicated that the 11 VOCs could be broadly divided into 2 groups, with α‐bisabolol, β‐caryophyllene, (E)‐2‐hexenal, (Z)‐3‐hexenal, limonene, methyl benzoate, methyl indole‐3‐acetic acid, methyl jasmonate, methyl salicylate as the first group and the rest (i.e., methyl linoleate and methyl linolenate) as a second. Abundance of VOCs in white ash phloem tissue and frass, nevertheless, did not attract T. planipennisi females. The concealed feeding of EAB larvae might explain the selection for detectable and reliable virbrational signals, instead of undetectable and relatively unreliable VOC cues from phloem and frass, in short‐range foraging by T. planipennisi. Alternatively, it is possible that T. planipennisi is not amenable to the Y‐tube olfactometer assay employed.     

Volatile compounds from young peach shoots attract males of oriental fruit moth in the field

Abstract

The oriental fruit moth (OFM) is one of the most serious pests of commercial fruit orchards worldwide. Newly planted peach trees in particular, can be very attractive for mated OFM females for oviposition. Samples of airborne host plant volatiles from intact young peach shoot tips and old leaves of the same potted plants were collected and analyzed with a gas chromatograph-mass spectrometer. Chemicals present in young shoot tips, but not in old leaves, were used for field trials. Moth capture by traps with the synthetic chemicals was compared to that of the standard terpinyl acetate (TA) food trap. The TA food trap caught OFM males and mated females, but tested synthetic chemicals trapped only OFM males. We observed that the mixture of (Z)-3-hexenyl acetate: (E)-β-ocimene: (E)-β-farnesene in proportion 1:2:2 attracted OFM males. Further, 1 mg of (E)-β-ocimene, and that of (E)-β-farnesene also attracted OFM males.     

Moisture content and nutrition as selection forces for emerald ash borer larval feeding behaviour

1. The exotic phloem‐feeding emerald ash borer (EAB), Agrilus planipennis, has killed tens of millions of North American ash trees (Fraxinus) since its first detection in the U.S.A. in 2002. Ash trees are killed by larval feeding in the cambial region, which disrupts translocation of photosynthates and nutrients. 2. We observed that EAB larvae feed predominantly downwards in naturally grown green ash trees, a behaviour confirmed in greenhouse‐grown black ash seedlings. Furthermore, biomass of larvae feeding downwards was greater than that for larvae feeding upwards. 3. We sought to determine the relative importance of four selection forces (i.e. gravity, moisture content, plant defence, and nutrition) in driving this downward feeding behaviour in this study. The gravity and plant defence (i.e. polyphenols) hypotheses were ruled out because even when seedlings were grown upside down, more EAB larvae moved upwards (towards the root area), and phloem tissue below the feeding site contained higher concentrations of defensive compounds than that above the feeding site. 4. The moisture content hypothesis was supported as phloem moisture above the feeding site decreased to levels reducing survivorship and biomass but was unaffected below. The nutrition hypothesis was also supported as the levels of 11 amino acids (mostly essential amino acids) below the feeding site were greater than those above. Furthermore, growth of larvae reared on an artificial diet deficient in protein and amino acids was worse than larvae reared in diet with complete ingredient or diet deficient in either protein or amino acids. 5. We conclude that moisture content and nutrients are two selective forces for the downward feeding behaviour of EAB larvae.     

Attraction of the egg parasitoid,Gonatocerus ashmeadi Girault (Hymenoptera: Mymaridae) to synthetic formulation of a (E)-β-ocimene and (E,E)-α-farnesene mixture

Glassy-winged sharpshooter (GWSS), Homalodisca vitripennis (Germar), is a vector of the xylem-inhabitant bacterium Xylella fastidiosa Wells et al., which causes Pierce’s disease of grapevines. Current GWSS control strategies in California, USA include area-wide insecticide applications and mass release of mymarid egg parasitoids, including Gonatocerus ashmeadi Girault. Gas chromatography–mass spectrometry was used to identify (E)-β-ocimene and (E,E)-α-farnesene as volatiles emitted from grapevines on which GWSS had previously fed and oviposited. Attractiveness of female G. ashmeadi to sugar-based formulations containing either (E)-β-ocimene, (E,E)-α-farnesene, or a mixture of both was evaluated using Y-tube olfactometry. When exposed to synthetic formulation containing a mixture of (E)-β-ocimene and (E,E)-α-farnesene vs. blank control, 61% of G. ashmeadi females initially chose the synthetic formulation. After the initial choice for a Y-tube arm, females visited the Y-tube arm connected to the source of formulation more often than it did to the arm connected to a blank control. There was no difference in the female’s time spent in the arm connected to the formulation. When testing formulations containing either (E)-β-ocimene or (E,E)-α-farnesene alone, there was a 1:1 ratio between the proportion of parasitoid’s first choice, visits, and residence time. Results suggest that synthetic formulations containing mixtures of certain plant volatiles may be used to localize GWSS egg parasitoids in vineyard systems. Results are discussed in the context of potential applications in GWSS biological control programs.     

Production of multiple terpenes of different chain lengths by subcellular targeting of multi-substrate terpene synthase in plants

Multi-substrate terpene synthases (TPSs) are distinct from typical TPSs that react with a single substrate. Although in vitro activity of few multi-substrate TPSs have been reported, in vivo characterization has not been well investigated for most of them. Here, a new TPS from Cananga odorata, CoTPS5, belonging to TPS-f subfamily was functionally characterized in vitro as well as in vivo. CoTPS5 reacted with multiple prenyl-pyrophosphate substrates of various chain lengths as a multi-substrate TPS. It catalyzed the formation of (E)-β-ocimene, (E,E)-α-farnesene and α-springene from geranyl pyrophosphate, (E,E)-farnesyl pyrophosphate and geranylgeranyl pyrophosphate, respectively. Upon transient expression in Nicotiana benthamiana, CoTPS5 localized to cytosol and produced only (E,E)-α-farnesene. However, expression of plastid-targeted CoTPS5 in N. benthamiana resulted in biosynthesis of all three compounds, (E)-β-ocimene, (E,E)-α-farnesene and α-springene. Similarly, transgenic Arabidopsis plants overexpressing plastid-targeted CoTPS5 showed stable and sustainable production of (E)-β-ocimene, (E,E)-α-farnesene and α-springene. Moreover, their production did not affect the growth and development of transgenic Arabidopsis plants. Our results demonstrate that redirecting multi-substrate TPS to a different intracellular compartment could be an effective way to prove in vivo activity of multi-substrate TPSs and thereby allowing for the production of multiple terpenoids simultaneously in plants.     

Chemical composition of volatiles emitted by Ziziphus jujuba during different growth stages

The volatiles emitted in vivo by different organs (leaf, bud flower, flower, green and red fruits) of Ziziphus jujuba were analysed using HS-SPME-GC/MS. A total of 144 compounds were identified corresponding to 94.6–99.4% of the whole aroma profile of jujube samples. The main constituents detected were (E, E)-α-farnesene, (E)-β-ocimene, perillene, γ-terpinene, cis-sabinene-hydrate, trans-sabinene-hydrate and 4-terpineol. The SPME analyses of the collected samples showed different patterns of emission and can contribute to understand their ecological interactions and fruit production management.     

Girdling increases survival and growth of emerald ash borer larvae on Manchurian ash

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Volatiles released from bean plants in response to agromyzid flies

Liriomyza sativae Blanchard and Liriomyza huidobrensis (Blanchard) (Diptera: Agromyzidae) are two invasive flies in China that have caused economical damage on vegetables and ornamental plants. In this article, we report the profiles of emitted volatiles from healthy, mechanically damaged, and leafminer-damaged bean, Phaseolus vulgaris L., plants. Among 25 emitted volatiles identified, (E)-2-hexen-1-al, (3E)-4,8-dimethyl-1,3,7-nonatriene (DMNT), (Z)-3-hexenyl acetate, (Z)-3-hexen-1-ol, (syn)- and (anti)-2-methylpropanal oxime, (syn)-2-methylbutanal oxime, linalool, and (E,E)-α-farnesene were consistently released from damaged bean plants. Combined amounts of these nine compounds made up more than 70% of the total volatiles emitted from each treatment. No qualitative differences in volatile emission were found between bean plants damaged by the two fly species; however, amounts of several major compounds induced by L. huidobrensis damage were significantly higher than those from plants damaged by L. sativae. The mechanically damaged plants released a higher proportion of green leaf volatiles than plants in the other treatments, whereas leafminer-damaged plants produced more terpenoids and oximes. Furthermore, the volatile profiles emitted from plants, damaged by adult leafminers, by second instar larvae, and even the plants with empty mines left by leafminer larvae (the pupal stage) were significantly different. The identification of volatile oximes released from damaged plants was confirmed and is discussed in a behavioral and biological control context.Electronic Supplementary Material Supplementary material is available for this article at and is accessible for authorized users.     

Drought stress increased survival and development of emerald ash borer larvae on coevolved Manchurian ash and implicates phloem‐based traits in resistance

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Interactions of root and leaf herbivores on purple loosestrife (<Emphasis Type="Italic">Lythrum salicaria</Emphasis>)

Interspecific interactions of herbivores sharing a host plant may be important in structuring herbivore communities. We investigated host plant-mediated interactions of root (Hylobius transversovittatus) and leaf herbivores (Galerucella calmariensis), released to control purple loosestrife (Lythrum salicaria) in North America, in field and potted plant experiments. In the potted plant experiments, leaf herbivory by G. calmariensis reduced H. transversovittatus larval survival (but not larval development) but did not affect oviposition preference. Root herbivory by H. transversovittatus did not affect either G. calmariensis fitness or oviposition preference. In field cage experiments, we found no evidence of interspecific competition between root and leaf herbivores over a 4-year period. Our data suggest that large populations of leaf beetles can negatively affect root-feeding larvae when high intensity of leaf damage results in partial or complete death of belowground tissue. Such events may be rare occurrences (or affected by experimental venue) since field data differed from data obtained from potted plant experiments, particularly at high leaf beetle densities. Interspecific interactions between G. calmariensis and H. transversovittatus are possible and may negatively affect either species, but this is unlikely to occur unless heavy feeding damage results in partial or complete plant death.     

Molecular and biochemical evolution of maize terpene synthase 10, an enzyme of indirect defense

Maize plants attacked by lepidopteran larvae emit a volatile mixture that consists mostly of the sesquiterpene olefins, (E)-α-bergamotene and (E)-β-farnesene. These volatiles are produced by the herbivore-induced terpene synthase TPS10 and attract natural enemies to the damaged plants. A survey of volatiles in maize lines and species of teosinte showed that the TPS10 products (E)-α-bergamotene and (E)-β-farnesene are consistently induced by herbivory, indicating that release of TPS10 volatiles is a defense trait conserved among maize and its wild relatives. Sequence comparison of TPS10 from maize and its apparent orthologs from four teosinte species demonstrated stabilizing selection on this defense trait. The teosinte volatiles and the enzymatic activity of the apparent TPS10 orthologs were not completely uniform but varied in the ratio of (E)-α-bergamotene to (E)-β-farnesene products formed. We identified a single amino acid in the active center which determines the ratio of (E)-α-bergamotene to (E)-β-farnesene and has changed during the evolution of maize and teosinte species. Feeding experiments with the substrate (Z,E)-farnesyl diphosphate revealed that this amino acid controls the rate of isomerization of the (E,E)-farnesyl carbocation intermediate to the (Z,E)-configuration.     

(E,E)-α-Farnesene as a host-induced plant volatile that attracts Apanteles taragamae (Hymenoptera: Braconidae) to host-infested cucumber plants

In tritrophic interactions between cucumber plants, the cucumber moth Diaphania indica Saunders (Lepidoptera: Crambidae) and a larval parasitoid Apanteles taragamae Viereck (Hymenoptera: Braconidae), female A. taragamae may use herbivore-induced plant volatiles (HIPVs) to locate their host. However, the specific compound or blend of chemicals attracting A. taragamae remains unknown. In this study, differences in volatiles released from uninfested, mechanically damaged and host-infested cucumber plants were examined by the headspace volatile collection method. Responses of the larval parasitoid A. taragamae to the volatile extracts were examined in a four-arm olfactometer. We also investigated the attraction of female A. taragamae to a single compound identified as an HIPV from host-infested cucumber plants. Parasitoids discriminated between the volatiles from uninfested, host-infested and mechanically damaged plants. Chemical analysis of headspace volatiles from host-infested cucumber plants showed that (E,E)-α-farnesene was released as a major component (73.1%). When (E,E)-α-farnesene was tested alone in the range of 1.7–170?ng, female parasitoids responded to 17?ng only. Therefore, tritrophic interactions between A. taragamae and D. indica appear to be partly mediated by (E,E)-α-farnesene.     

Nitrogen deficiency induced changes of free amino acids and coumarin contents in the leaves of Matricaria chamomilla

Through o-hydroxycinnamic acids, the biosynthesis of coumarins is connected with aromatic amino acid metabolism and nitrogen uptake. Therefore the quantitative changes in levels of some free amino acids and coumarins (herniarin and its glucosidic precursors (Z) - and (E)-2-β-D-glucopyranosyloxy-4-methoxycinnamic acids; umbelliferone) in the leaf rosettes of chamomile (Matricaria chamomilla L.) subjected to nitrogen deficiency were studied. Nitrogen content decreased in the leaf rosettes and in the roots of N-deficient plants during the course of the experiment, but these plants produced significantly higher root biomass. Among secondary metabolites, the sum of 2-β-D-glucopyranosyloxy-4-methoxycinnamic acids increased sharply, herniarin increased slowly and the content of umbelliferone was low in N-deficient plants. We have concluded that nitrogen deficiency is not an inducing factor for stress accumulation of herniarin and umbelliferone. A decrease in levels of all detected amino acids, besides histidine, was found. Within aromatic amino acids, tyrosine was the most abundant. The content of free phenylalanine was significantly lower in both, control and N-deficient plants when compared to the content of tyrosine. In this view, the increase of herniarin glucosidic precursors is apparently due to enhancing phenylalanine ammonia-lyase activity under nitrogen deficiency and nitrogen-free carbon skeletons are shunted in to the phenylpropanoid metabolism, including biosynthesis of (Z)-and (E)-2-β-D-glucopyranosyloxy-4-methoxycinnamic acids.     

Development of multi-component non-sex pheromone blends to monitor both sexes of Cydia pomonella (Lepidoptera: Tortricidae)

Nineteen host plant volatiles (HPVs) were screened for attractivity to adult codling moth Cydia pomonella (L.) as a fourth component of core blends (3K) including (E,Z)-2,4-ethyl decadienoate, (E)-4,8-dimethyl-1,3,7-nonatriene and acetic acid. Each new quaternary combination was compared with a previously reported attractive bisexual lure (4K), consisting of the 3K blend plus 6-ethenyl-2,2,6-trimethyloxan-3-ol (pyranoid linalool oxide, pyrLOX). All lure evaluations were conducted in apple, Malus domestica (Borkhausen). Several compounds were found to significantly lower total and/or female catches when added to the 3K blend, including (Z)-3-hexenol, (E)-2-hexanal and hexyl butanoate (female and total moths), and (Z)-3-hexenyl acetate and linalool (female moths). Other compounds when added to the 3K blend did not increase or decrease moth catches, including methyl salicylate, (E)-β-ocimene, limonene, β-caryophyllene, butyl hexanoate, farnesol, terpineol, terpinen-4-ol and α-pinene. A few added compounds significantly increased moth catches compared with the 3K blend, including β-pinene (male moths), (Z)-jasmone (male and total moths), (E)-β-farnesene and β-myrcene (female and total moths), and (E,E)-α-farnesene (male, female, and total moths). In addition, each of these five compounds when added to the 3K core blend performed similarly to the 4K lure (male, females, and total moths). Further studies should expand these results through tests of these and other new blends with a range of component ratios and total loading amounts. Field trials should also be replicated within all host crops of codling moth and across major geographical production regions.     

Four terpene synthases produce major compounds of the gypsy moth feeding-induced volatile blend of Populus trichocarpa

After herbivore damage, many plants increase their emission of volatile compounds, with terpenes usually comprising the major group of induced volatiles. Populus trichocarpa is the first woody species with a fully sequenced genome, enabling rapid molecular approaches towards characterization of volatile terpene biosynthesis in this and other poplar species. We identified and characterized four terpene synthases (PtTPS1-4) from P. trichocarpa which form major terpene compounds of the volatile blend induced by gypsy moth (Lymantria dispar) feeding. The enzymes were heterologously expressed and assayed with potential prenyl diphosphate substrates. PtTPS1 and PtTPS2 accepted only farnesyl diphosphate and produced (−)-germacrene D and (E,E)-α-farnesene as their major products, respectively. In contrast, PtTPS3 and PtTPS4 showed both mono- and sesquiterpene synthase activity. They produce the acyclic terpene alcohols linalool and nerolidol but exhibited opposite stereospecificity. qRT-PCR analysis revealed that the expression of the respective terpene synthase genes was induced after feeding of gypsy moth caterpillars. The TPS enzyme products may play important roles in indirect defense of poplar to herbivores and in mediating intra- and inter-plant signaling.