Journal of Chemical Ecology

Klarica, Jasmin; Bittner, Lukas; Pallua, Johannes; Pezzei, Christine; Huck-Pezzei, Verena; Dowell, Floyd; Schied, Johannes; Bonn, Günther; Huck, Christian; Schlick-Steiner, Birgit; Steiner, Florian

doi: 10.1007/s10886-011-9956-xpmid: 21537901

Correct species identification is a precondition for many ecological studies. Morphologically highly similar, i.e., cryptic, species are an important component of biodiversity but particularly difficult to discriminate and therefore understudied ecologically. To find new methods for their rapid identification, thus, is important. The cuticle’s chemical signature of insects often is unique for species. Near-infrared spectroscopy (NIRS) can capture such signatures. Imaging NIRS facilitates precise positioning of the measurement area on biological objects and high-resolution spatial capturing. Here, we tested the applicability of imaging NIRS to the discrimination of cryptic species by using the ants Tetramorium caespitum and T. impurum. The classification success of Partial Least Squares Regression was 98.8%. Principal Component Analysis grouped spectra of some T. impurum individuals with T. caespitum. Combined with molecular-genetic and morphological evidence, this result enabled us to pose testable hypotheses about the biology of these species. We conclude that discrimination of T. caespitum and T. impurum with imaging NIRS is possible, promising that imaging NIRS could become a time- and cost-efficient tool for the reliable discrimination of cryptic species. This and the direct facilitation of potential biological insight beyond species identification underscore the value of imaging NIRS to ecology.

Jang, Eric; Khrimian, Ashot; Siderhurst, Matthew

doi: 10.1007/s10886-011-9963-ypmid: 21614534

Oriental fruit fly, Bactrocera dorsalis (Hendel), males are attracted to the natural phenylpropanoid methyl eugenol (ME). They feed compulsively on ME and metabolize it to ring and side-chain hydroxylated compounds that have both pheromonal and allomonal properties. Previously, we demonstrated that mono-fluorination at the terminal carbon of the ME side-chain significantly reduced metabolic side-chain hydroxylation, while mono-fluorination of ME at position 4 of the aromatic ring blocked ring-hydroxylation but surprisingly enhanced side-chain hydroxylation. Here, we demonstrated that the introduction of fluorine atoms on both the ring and side-chain of ME blocks both positions that undergo enzymatic hydroxylation and, in particular, completely inhibits oxidative biotransformation of the allyl group. In laboratory experiments, B. dorsalis males initially were more attracted to both 1-fluoro-4,5-dimethoxy-2-(3,3-difluoro-2-propenyl)benzene (I) and 1-fluoro-4,5-dimethoxy-2-(3-fluoro-2-propenyl)benzene (II) than to ME. However, both I and II were taken up by flies at rates significantly less than that of ME. Flies fed with difluoroanalog II partially metabolized it to 5-fluoro-4-(3-fluoroprop-2-en-1-yl)-2-methoxyphenol (III), and flies fed with trifluoroanalog I produced 4-(3,3-difluoroprop-2-en-1-yl)-5-fluoro-2-methoxyphenol (V), but the rates of metabolism relative to rates of intakes were much lower compared to those of ME. Flies that consumed either the tri- or difluorinated analog showed higher post-feeding mortality than those that fed on methyl eugenol. In field trials, trifluoroanalog I was ∼90% less attractive to male B. dorsalis than ME, while difluoroanalog II was ∼50% less attractive. These results suggest that increasing fluorination can contribute to fly mortality, but the trade off with attractancy makes it unlikely that either a di or trifluorinated ME would be an improvement over ME for detection and/or eradication of this species.

Proffit, Magali; Birgersson, Göran; Bengtsson, Marie; Reis, Ronaldo; Witzgall, Peter; Lima, Eraldo

doi: 10.1007/s10886-011-9961-0pmid: 21559877

The tomato leafminer Tuta absoluta (Lepidoptera: Gelechiidae) is a devastating pest of cultivated tomato Solanum lycopersicum throughout South and Central America and Europe. We aimed to characterize the behavioral mechanisms and the chemical cues involved in host selection of T. absoluta females by chemical analysis of tomato leaf volatiles, wind tunnel attraction assays, and oviposition bioassays. Tomato leaf odor elicited in mated females upwind orientation flight followed by landing as well as egg-laying, demonstrating the essential role of plant volatiles in T. absoluta host-finding behavior. In wind tunnel and oviposition choice experiments, T. absoluta females significantly preferred tomato S. lycopersicum over wild tomato Solanum habrochaites, which is resistant to larval feeding. This indicates that leaf volatiles provide information on the suitability of plants as larval hosts. Mated females also discriminated three cultivars of S. lycopersicum according to their volatile profiles. Headspace collections from leaves of these three cultivars contained large amounts of β-phellandrene, followed by limonene, 2-carene, and (E)-β-caryophyllene, which together accounted for more than 70% of tomato foliage headspace. Most leaf volatiles were released by all three cultivars, but they showed significant differences with respect to the presence of a few minor compounds and blend proportion. This is an initial study of the volatile signatures that mediate attraction and oviposition of tomato leafminer T. absoluta in response to its main host, tomato.

Honda, Keiichi; Ômura, Hisashi; Chachin, Mamoru; Kawano, Seiji; Inoue, Takashi

doi: 10.1007/s10886-011-9965-9pmid: 21573758

Papilio maackii females prefer a rutaceous plant, Phellodendron amurense, for oviposition, whereas another semi-sympatric Rutaceae feeder, Papilio protenor, never exploits this plant as a host in nature. However, the larvae of both species perform well on this plant in the laboratory. Phellamurin, a flavonoid present in the organic fraction from P. amurense inhibits egg laying by P. protenor. We examined whether phellamurin is involved in the differential acceptance of P. amurense by the two butterflies. The ovipositing females of P. maackii readily accepted P. amurense and a methanolic extract of the foliage, while P. protenor rejected them entirely. However, the aqueous fraction derived from the extract elicited significant oviposition responses of similar levels from the two species. Phellamurin did not induce oviposition behavior in P. protenor females. In contrast, P. maackii was stimulated to oviposit by phellamurin at concentrations exceeding 0.2%. The response was dose-dependent and reached ca. 70% at 2% phellamurin, which is approximately equivalent to its natural abundance in young leaves of P. amurense. Since the aqueous fraction was very stimulatory to both species, the combined effect of phellamurin and the aqueous fraction on oviposition was tested. The addition of phellamurin to the aqueous fraction enhanced the ovipositional activity of P. maackii, but dramatically suppressed the oviposition response of P. protenor even at 0.1% concentration. These results, taken together with those obtained from electrophysiological recordings with foretarsal chemosensilla, indicate that phellamurin acts as an oviposition stimulant for P. maackii, and as a potent deterrent for P. protenor. The results suggest that host range expansion or host shifts may be made by ovipositing females that overcome phytochemical barriers.

Fontana, Anna; Held, Matthias; Fantaye, Chalie; Turlings, Ted; Degenhardt, Jörg; Gershenzon, Jonathan

doi: 10.1007/s10886-011-9967-7pmid: 21607717

Plant volatile compounds induced by herbivore attack have been demonstrated to provide a signal to herbivore enemies such as parasitic wasps that use these volatiles to locate their hosts. However, in addition to herbivore-induced volatiles, plants often release volatiles constitutively. We assessed the interaction between herbivore-induced and constitutively released volatiles of maize in the attraction of the wasp Cotesia marginiventris that parasitizes herbivorous lepidopteran larvae feeding on maize. Experiments were carried out with olfactometers in which the sources of volatiles were transgenic Arabidopsis thaliana plants overexpressing maize sesquiterpene synthases that produce blends of herbivore-induced or constitutive compounds. We found that the constitutive volatiles of maize terpene synthase 8 (TPS8) were attractive to C. marginiventris, just like the herbivore-induced volatiles of TPS10 studied earlier. A mixture of both the TPS8 and TPS10 volatile blends, however, was more effective in parasitoid attraction, indicating that constitutively released sesquiterpenes enhance the attraction of those induced by herbivores. While C. marginiventris did not distinguish among the volatiles of TPS8, TPS10, nor those of another maize sesquiterpene synthase (TPS5), when these blends were combined, their attractiveness to the wasp appeared to increase with the complexity of the blend.

Radville, Laura; Chaves, Arielle; Preisser, Evan

doi: 10.1007/s10886-011-9962-zpmid: 21573865

Herbivores can trigger a wide array of morphological and chemical changes in their host plants. Feeding by some insects induces a defensive hypersensitive response, a defense mechanism consisting of elevated H2O2 levels and tissue death at the site of herbivore feeding. The invasive hemlock woolly adelgid Adelges tsugae (‘HWA’) and elongate hemlock scale Fiorinia externa (‘EHS’) feed on eastern hemlocks; although both are sessile sap feeders, HWA causes more damage than EHS. The rapid rate of tree death following HWA infestation has led to the suggestion that feeding induces a hypersensitive response in hemlock trees. We assessed the potential for an herbivore-induced hypersensitive response in eastern hemlocks by measuring H2O2 levels in foliage from HWA-infested, EHS-infested, and uninfested trees. Needles with settled HWA or EHS had higher H2O2 levels than control needles, suggesting a localized hypersensitive plant response. Needles with no direct contact to settled HWA also had high H2O2 levels, suggesting that HWA infestation may induce a systemic defense response in eastern hemlocks. There was no similar systemic defensive response in the EHS treatment. Our results showed that two herbivores in the same feeding guild had dramatically different outcomes on the health of their shared host.

Adfa, Morina; Hattori, Yosuke; Yoshimura, Tsuyoshi; Komura, Kenichi; Koketsu, Mamoru

doi: 10.1007/s10886-011-9968-6pmid: 21598014

We synthesized 23 6-alkoxycoumarin derivatives, 20 of which are novel compounds. The structures of all compounds were confirmed by NMR, MS, and elemental analysis, and their antifeedant and termiticidal activities against Coptotermes formosanus Shiraki were examined. In a no-choice test, 6-(2-pentynyloxy)coumarin (2v), 6-(2-butynyloxy)coumarin (2u), 6-(2-octynyloxy)coumarin (2w), and 6-methoxycoumarin (2a), demonstrated high termiticidal activity at a concentration of 10 μmol. At a concentration of 5 μmol, 6-(2-butynyloxy)coumarin (2u) produced the highest mortality among the compounds tested. On the other hand, all of the 6-alkoxycoumarins showed antifeedant activity at both concentrations, except 6-octadecyloxycoumarin (2j) that was inactive at 5 μmol. Among the 23 compounds and the control, 6-ethoxycoumarin (2b), 6-isopropoxycoumarin (2d), and 6-isobutoxycoumarin (2f) exhibited the highest antifeedant activity with no mass loss (0.00%) at a concentration of 10 μmol. Our findings indicate that the presence of alkenyloxy and alkynyloxy groups was important for the termiticidal activity, while the incorporation of alkoxy groups with longer alkyl chains tended to reduce both the termiticidal and antifeedant activities. Furthermore, short chain alkoxy and arylalkoxy-substituted analogs showed good antifeedant activity, but methoxy groups on the benzene ring had a negative effect.

Wallis, Christopher; Huber, Dezene; Lewis, Kathy

doi: 10.1007/s10886-011-9958-8pmid: 21537900

Lodgepole pines, Pinus contorta Douglas ex Louden var. latifolia Engelm. ex S. Watson, are encountering increased abiotic stress and pest activity due to recent increases in temperature and changes in precipitation throughout their range. This tree species counters these threats by producing secondary metabolites, including phenolics and terpenoids. We examined foliar levels of lignin, soluble phenolics, monoterpenoids, sesquiterpenoids, and diterpenoids in 12 stands in British Columbia, Canada. We used these data to assess associations among foliar secondary metabolite levels and ecosystem, geographic, and climatic variables. Regressions were also performed to observe which combinations of variables best explained secondary metabolite variance. Stands of P. c. latifolia in the Coastal Western Hemlock and Interior Cedar/Hemlock biogeoclimatic zones had consistently greater foliar levels of almost all measured secondary metabolites than did other stands. Lignin was present in greater amounts in Boreal White/Black Spruce ecosystem (i.e., northern) stands than in southern stands, suggesting a role for this metabolite in pine survival in the boreal forest. Attempts to develop regression models with geographic and climatic variables to explain foliar secondary metabolite levels resulted in multiple models with similar predictive capability. Since foliar secondary metabolite levels appeared to vary most between stand ecosystem types and not as much due to geographic and climatic variables, metabolic profiles appeared best matched to the stress levels within local environments. It is unknown if differences in secondary metabolite levels are the result of genetic adaptation or phenotypic plasticity, but results from this and other studies suggest that both are important. These results are interpreted in light of ongoing efforts to assist in the migration of certain populations of P. c. latifolia northward in an effort to counter predicted effects of climate change.

Giudice, Daniela; Riedel, Michael; Rostás, Michael; Peri, Ezio; Colazza, Stefano

doi: 10.1007/s10886-011-9957-9pmid: 21547535

Egg parasitoids are able to find their hosts by exploiting their chemical footprints as host location cues. In nature, the apolar epicuticular wax layer of plants that consists of several classes of hydrocarbons serves as the substrate that retains these contact kairomones. However, experiments on chemical footprints generally have used filter paper as substrate to study insect behavior. Here, we explored the ability of Trissolcus basalis (Scelionidae) females to discriminate between footprint cues left by male and female Nezara viridula (Pentatomidae) on leaves of their host plant Brassica oleracea (broccoli). Furthermore, we analyzed the chemical composition of the outermost wax layer of broccoli leaves to evaluate the degree of overlap in insect and plant cuticular hydrocarbons that could lead to masking effects in the detection of footprint cues. Our results showed that B. oleracea epicuticular wax retains the chemical footprints of adult bugs and allows T. basalis females to differentiate hosts of different sex. Traces of female bugs elicited more extensive searching behavior in egg parasitoids than traces of males. The application of n-nonadecane, a compound specific to male N. viridula, on the tarsi of female bugs prevented parasitoid females from distinguishing between host male and host female footprints. Analyses of B. oleracea leaves revealed that epicuticular waxes were mainly composed of linear alkanes, ketones, and secondary alcohols. Alkanes were dominated by n-nonacosane (nC29) and n-hentriacontane (nC31), while male-specific n-nonadecane (nC19) was absent. The ecological significance of these results for parasitoid host location behavior is discussed.

González, Jorge; Cusumano, Antonino; Williams, Howard; Colazza, Stefano; Vinson, S.

doi: 10.1007/s10886-011-9960-1pmid: 21552995

Contact kairomones from the host mud dauber wasp Trypoxylon politum Say (Hymenoptera: Crabronidae) that mediate behavioral responses of its ectoparasitoid Melittobia digitata Dahms (Hymenoptera: Eulophidae) were investigated. Chemical residues from host by-products, the cocoon, and the meconium, induced arrestment behavior of macropterous female parasitoids, while those from the host stage attacked, i.e., the prepupa, did not. Melittobia digitata response to polar and apolar extracts of host by-products indicated kairomone(s) solubility mainly in hexane. GC and GC/MS analysis of cocoon and meconium apolar extracts revealed a mixture of linear carboxylic acids from C6 to C18, and both extracts contained almost identical compounds. When a reconstructed blend of host by-product carboxylic acids was tested, M. digitata females showed only a weak response, thus suggesting that other unidentified compounds present in small quantities also may be involved. Melittobia digitata’s response to contact kairomones was innate and not affected by previous host exposure experience. Our results provide evidence of contact kairomone exploitation in the genus Melittobia. The ecological significance of these findings in the host selection process of M. digitata is discussed.