Journal of Chemical Ecology

Fantaye, Chalie; Köpke, Diana; Gershenzon, Jonathan; Degenhardt, Jörg

doi: 10.1007/s10886-015-0556-zpmid: 25893788

The sesquiterpene (E)-β-caryophyllene is emitted from maize (Zea mays) leaves and roots in response to herbivore attack. This compound serves as a signal for the attraction of herbivore enemies and is present in most European maize varieties. However, most North American maize lines have lost the ability to produce (E)-β-caryophyllene. Previously, we showed that restoring the ability to synthesize (E)-β-caryophyllene in a non-producing maize line improved its resistance against the root herbivore Diabrotica virgifera virgifera. However, it is largely unknown whether this modification affects the resistance to other pests. In this study, we investigated the response of constitutively (E)-β-caryophyllene-producing transgenic lines to infection by a hemibiotrophic fungus Colletotrichum graminicola. Our results showed that restoring (E)-β-caryophyllene synthesis in a Hi-II genetic background enhanced the susceptibility of the plant to C. graminicola infection rather than increasing its resistance. This modification did not alter the baseline levels of plant defense hormones and metabolites. Nor did (E)-β-caryophyllene production modify the expression of anti-fungal defense genes. Instead, the addition of (E)-β-caryophyllene seemed to directly stimulate fungal growth. In an in vitro antifungal assay, we found that (E)-β-caryophyllene stimulated hyphal growth of C. graminicola and Fusarium graminearum. Thus, although restoring (E)-β-caryophyllene production in a non-producing maize line may improve the resistance of the plant against herbivores, it may compromise its resistance to major fungal pathogens. This might explain the loss of (E)-β-caryophyllene during maize breeding in environments where C. graminicola and Fusarium graminearum are prevalent.

Achotegui-Castells, Ander; Danti, Roberto; Llusià, Joan; Rocca, Gianni; Barberini, Sara; Peñuelas, Josep

doi: 10.1007/s10886-015-0554-1pmid: 25740205

Seiridium cardinale, the main fungal pathogen responsible for cypress bark canker, is the largest threat to cypresses worldwide. The terpene response of canker-resistant clones of Italian cypress, Cupressus sempervirens, to two differently aggressive isolates of S. cardinale was studied. Phloem terpene concentrations, foliar terpene concentrations, as well as foliar terpene emission rates were analyzed 1, 10, 30, and 90 days after artificial inoculation with fungal isolates. The phloem surrounding the inoculation point exhibited de novo production of four oxygenated monoterpenes and two unidentified terpenes. The concentrations of several constitutive mono- and diterpenes increased strongly (especially α-thujene, sabinene, terpinolene, terpinen-4-ol, oxygenated monoterpenes, manool, and two unidentified diterpenes) as the infection progressed. The proportion of minor terpenes in the infected cypresses increased markedly from the first day after inoculation (from 10 % in the control to 30–50 % in the infected treatments). Foliar concentrations showed no clear trend, but emission rates peaked at day 10 in infected trees, with higher δ-3-carene (15-fold) and total monoterpene (10-fold) emissions than the control. No substantial differences were found among cypresses infected by the two fungal isolates. These results suggest that cypresses activate several direct and indirect chemical defense mechanisms after infection by S. cardinale.

Chen, Gao; Jürgens, Andreas; Shao, Lidong; Liu, Yang; Sun, Weibang; Xia, Chengfeng

doi: 10.1007/s10886-015-0563-0pmid: 25835570

By emitting scent resembling that of organic material suitable for oviposition and/or consumption by flies, sapromyophilous flowers use these flies as pollinators. To date, intensive scent analyses of such flowers have been restricted to Apocynaceae, Annonaceae, and Araceae. Recent studies have suggested that the wide range of volatile organic compounds (VOCs) from sapromyophilous flowers play an important role in attracting saprophagous flies by mimicking different types of decomposing substrates (herbivore and carnivore feces, carrion, and the fruiting bodies of fungi, etc.). In this study, we report the flower visitors and the floral VOCs of Stemona japonica (Blume) Miquel, a species native to China. The flowers do not produce rewards, and pollinators were not observed consuming pollen, thus suggesting a deceptive pollination system. Headspace samples of the floral scent were collected via solid-phase micro-extraction and analysed by gas chromatography coupled with mass spectrometry. Main floral scent compounds were 1-pyrroline (59.2 %), 2-methyl-1-butanol (27.2 %), and 3-methyl-1-butanol (8.8 %), and resulted in a semen-like odor of blooming flowers. The floral constituents of S. japonica were significantly different from those found in previous sapromyophilous plants. An olfaction test indicated that 1-pyrroline is responsible for the semen-like odor in S. japonica flowers. Main flower visitors were shoot flies of the genus Atherigona (Muscidae). Bioassays using a mixture of all identified floral volatiles revealed that the synthetic volatiles can attract Atherigona flies in natural habitats. Our results suggest that the foul-smelling flowers of S. japonica may represent a new type of sapromyophily through scent mimicry.

Eilers, Elisabeth; Pauls, Gerhard; Rillig, Matthias; Hansson, Bill; Hilker, Monika; Reinecke, Andreas

doi: 10.1007/s10886-015-0559-9pmid: 25795090

Most studies on rhizosphere chemicals are carried out in substrate-free set-ups or in artificial substrates using sampling methods that require an air flow and may thus cause disturbance to the rhizosphere. Our study aimed to develop a simplified and inexpensive system that allows analysis of rhizosphere chemicals at experimentally less disturbed conditions. We designed a mesocosm in which volatile rhizosphere chemicals were sampled passively (by diffusion) without air- and water flow on polydimethylsiloxane-(PDMS) tubes. Dandelion (Taraxacum sect. ruderalia) was used as model plant; roots were left undamaged. Fifteen volatiles were retrieved from the sorptive material by thermal desorption for analysis by gas chromatography/mass spectrometry (GC/MS). Furthermore, three sugars were collected from the rhizosphere substrate by aqueous extraction and derivatized prior to GC/MS analysis. In order to study how the quantity of detected rhizosphere compounds depends on the type of soil or substrate, we determined the matrix-dependent recovery of synthetic rhizosphere chemicals. Furthermore, we compared sorption of volatiles on PDMS tubes with and without direct contact to the substrate. The results show that the newly designed mesocosm is suitable for low-invasive extraction of volatile and non-volatile compounds from rhizospheres. We further highlight how strongly the type of substrate and contact of PDMS tubes to the substrate affect the detectability of compounds from rhizospheres.

Joachim, Christoph; Weisser, Wolfgang

doi: 10.1007/s10886-015-0555-0pmid: 25779875

Insect natural enemies use several environmental cues for host/prey finding, and adjust their foraging behavior according to these signals. In insects, such cues are mainly chemical, derived from the host plant or the prey itself. The aphid alarm pheromone, (E)-β-farnesene (EBF), is believed to be such a cue, because several aphid enemies are able to perceive EBF and show attractant behavior. These studies are, however, based mainly on electroantennogram or olfactometer assays, and often use unnaturally high pheromone concentrations. It is, therefore, unclear if EBF is used to locate prey in the field when only naturally released amounts are present. We monitored the frequencies and durations of plant visits by aphid natural enemies in the field using long-duration camera observations. By placing pheromone releasers emitting no, natural or exaggerated amounts of EBF next to small colonies of pea aphids (Acyrthosiphon pisum), we analyzed if EBF presence altered long-range foraging behavior of natural enemies. Thirteen potential groups of aphid natural enemies were observed in 720 hr of analyzed video data. There was no effect of EBF on the number of predator visits to an aphid colony, or on predator patch residence times. The number of plant visits increased at exaggerated EBF amounts but not at natural EBF levels. We conclude that while there may be potential for use of high EBF concentrations for agricultural pest management strategies, an ecological role of EBF as a kairomone in a natural context is doubtful.

Geiselhardt, Sven; Hilker, Monika; Müller, Frank; Kozlov, Mikhail; Zvereva, Elena

doi: 10.1007/s10886-015-0558-xpmid: 25804685

We explored the inter- and intrapopulation variability in the larval defensive chemistry of the leaf beetle Chrysomela lapponica with respect to the salicylic glycoside (SG) content of its host species. Secretions of larvae from three populations associated in nature with SG-poor willows contained nearly twice as many components and 40-fold higher concentrations of autogenously produced isobutyrates and 2-methylbutyrates than secretions of larvae from three populations associated with SG-rich willows, which in turn had 200-fold higher concentrations of host-derived salicylaldehyde. Reciprocal transfer experiments showed that the larvae from populations associated with SG-rich willows did not produce appreciable amounts of butyrates on either SG-rich or SG-poor willows, while populations feeding on several SG-poor willow species retained the ability for efficient sequestration of SGs, along with their ability to produce high amounts of isobutyrates and 2-methylbutyrates. Only the populations associated with SG-poor willows demonstrated among-family variation in the composition of defensive secretion and differential responses of individual families to willows with alternative SG levels, which can be seen as the prerequisites for shifting to novel hosts. These non-specialized populations show a dual defensive strategy, which corresponds to the ancestral state of this species, while populations that fully depend on host-derived toxins (feeding on SG-rich willows) or have lost the ability to produce salicylaldehyde (feeding on birches) are most deviant from the ancestral state. The results indicate that defensive strategies may differ between populations within a species, and suggest that this variation reduces extinction risks and maintains the high ecological diversity and wide distribution of C. lapponica.

Vuts, József; Powers, Stephen; Caulfield, John; Pickett, John; Birkett, Michael

doi: 10.1007/s10886-015-0560-3pmid: 25786892

Males of Acanthoscelides obtectus (Coleoptera: Chrysomelidae, Bruchinae) emit methyl (E,R)-2,4,5-tetradecatrienoate that attracts females for mating. This study identified further roles for this compound in the sexual behavior of A. obtectus. Earlier observations revealed that males touched females with their antennae while tandem-running with them and initiated mounting and copulation, whereas they showed no such behavior toward other males. A series of subsequent laboratory choice tests were set up to establish if certain cuticular compounds aid contact sex recognition in A. obtectus. Males chose virgin females over other males. The activity toward females could be eliminated by rinsing with hexane, but was regained by application of female extract onto previously rinsed females. Gas chromatographic (GC) comparison of hexane extracts revealed the presence of two male-specific compounds, methyl (E,R)-2,4,5-tetradecatrienoate and octadecanal, which were absent from the behaviorally active female samples. Of the two compounds, methyl (E,R)-2,4,5-tetradecatrienoate was found to be responsible for the inhibition of male sexual behavior, similar to that observed with crude male extracts applied to virgin females. Furthermore, males preferred virgin over mated females. GC analyses revealed the presence of methyl (E,R)-2,4,5-tetradecatrienoate in mated females in amounts sufficient to curtail mating attempts. It appears that methyl (E,R)-2,4,5-tetradecatrienoate, besides being a male-produced sex pheromone, acts as a male-recognition signal in A. obtectus. Males also transfer it onto females during mating, resulting in mated females being avoided by courting males.

Silk, P.; Ryall, K.; Mayo, P.; MaGee, D.; Leclair, G.; Fidgen, J.; Lavallee, R.; Price, J.; McConaghy, J.

doi: 10.1007/s10886-015-0562-1pmid: 25786893

The emerald ash borer, Agrilus planipennis (Coleoptera: Buprestidae) (EAB), is an invasive species causing unprecedented levels of mortality to ash trees in its introduced range. The female-produced sex pheromone of EAB has been shown to contain the macrocyclic lactone (3Z)-dodecen-12-olide. This compound and its geometrical isomer, (3E)-dodecen-12-olide, have been demonstrated previously to be EAG active and, in combination with a host-derived green leaf volatile, (3Z)-hexenol, to be attractive to male EAB in green prism traps deployed in the ash tree canopy. In the current study, we show that the saturated analog, dodecan-12-olide, is similarly active, eliciting an antennal response and significant attraction of EAB in both olfactometer and trapping bioassays in green traps with (3Z)-hexenol. Conformational modeling of the three lactones reveals that their energies and shapes are very similar, suggesting they might share a common receptor in EAB antennae. These findings provide new insight into the pheromone ecology of this species, highlighting the apparent plasticity in response of adults to the pheromone and its analog. Both of the unsaturated isomers are costly to synthesize, involving multistep, low-yielding processes. The saturated analog can be made cheaply, in high yield, and on large scale via Mitsunobu esterification of a saturated ω-hydroxy acid or more simply by Baeyer-Villiger oxidation of commercially available cyclododecanone. The analog can thus provide an inexpensive option as a lure for detection surveys as well as for possible mitigation purposes, such as mating disruption.

Kuenen, L.; Siegel, Joel

doi: 10.1007/s10886-015-0557-ypmid: 25801328

The type of solvent and the volume used to load pheromone components onto rubber septa had significant effects on pheromone release ratios, the variability of those release ratios, and the recoverability of the volatile components during subsequent extraction with hexane. Volatile release ratios of synthetic Oriental fruit moth (OFM) pheromone and additional volatile compounds were determined using a gas chromatograph column as a volatile trap for rapid (≤1 hr) analysis from individual rubber septa. Volatile compound solutions were prepared in hexane, pentane, CH2Cl2, and methyl tert-butyl ether, and a 10, 33, or 100 μl aliquot of each solution was applied to rubber septa. Septa loaded with 100 μl of CH2Cl2 emitted significantly (P < 0.05) higher alcohol: acetate (OH:Ac) ratios than septa loaded with the other solvents, which were all similar. Release ratios of the alcohol and acetate components of the OFM pheromone components were assessed over a 3 week period using septa loaded with each solvent. Regardless of loading solvent, the OFM OH:Ac ratios declined logarithmically over 3 weeks; however, the decay slope from septa loaded with CH2Cl2 solutions was different from those of the other three solvents, which were nearly all the same. A high variability in OH:Ac release ratios was measured overall, regardless of the solvent used or the volume it was applied in. Four compounds of near-equal mass: 1-dodecanol, 1-dodecanal, methyl decanoate, and tridecane emitted different release ratios dependent on the solvent, hexane or CH2Cl2, with which a septum was loaded. The more polar and the greater the mass of the test compound, the slower it was emitted from a septum regardless of solvent. These combined results plus comparisons to earlier reports, suggest that researchers should empirically assess the release ratios from septa to be used in bioassays rather than just reporting the type of septum, ratios of compounds applied and solvent used to prepare them.

Johnson, Nicholas; Tix, John; Hlina, Benjamin; Wagner, C.; Siefkes, Michael; Wang, Huiyong; Li, Weiming

doi: 10.1007/s10886-015-0561-2pmid: 25795091

Spermiating male sea lamprey (Petromyzon marinus) release a sex pheromone, of which a component, 7α, 12α, 24-trihydoxy-3-one-5α-cholan-24-sulfate (3kPZS), has been identified and shown to induce long distance preference responses in ovulated females. However, other pheromone components exist, and when 3kPZS alone was used to control invasive sea lamprey populations in the Laurentian Great Lakes, trap catch increase was significant, but gains were generally marginal. We hypothesized that free-ranging sea lamprey populations discriminate between a partial and complete pheromone while migrating to spawning grounds and searching for mates at spawning grounds. As a means to test our hypothesis, and to test two possible uses of sex pheromones for sea lamprey control, we asked whether the full sex pheromone mixture released by males (spermiating male washings; SMW) is more effective than 3kPZS in capturing animals in traditional traps (1) en route to spawning grounds and (2) at spawning grounds. At locations where traps target sea lampreys en route to spawning grounds, SMW-baited traps captured significantly more sea lampreys than paired 3kPZS-baited traps (~10 % increase). At spawning grounds, no difference in trap catch was observed between 3kPZS and SMW-baited traps. The lack of an observed difference at spawning grounds may be attributed to increased pheromone competition and possible involvement of other sensory modalities to locate mates. Because fishes often rely on multiple and sometimes redundant sensory modalities for critical life history events, the addition of sex pheromones to traditionally used traps is not likely to work in all circumstances. In the case of the sea lamprey, sex pheromone application may increase catch when applied to specifically designed traps deployed in streams with low adult density and limited spawning habitat.