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Journal of Chemical Ecology (v.25, #1)

Editors' Note (pp. 1-1).

Inducible Nicotine Production in Native Nicotiana as an Example of Adaptive Phenotypic Plasticity by Ian T. Baldwin (pp. 3-30).
Nicotine, an inducible defense in a number of Nicotiana species, exemplifies adaptive phenotypic plasticity. The mechanisms responsible for its production are reviewed, and the induced character states are characterized allometrically in order to understand how inducibility changes over ontogeny responds to environmental variables that influence plant growth, and to relate inducible production to plant fitness correlates. The empirical evidence for fitness costs and benefits of inducible nicotine production are considered, and the physiological and ecological mechanisms potentially responsible for the costs are considered. An intimate understanding of the plant's natural history is an essential prerequisite to understanding these costs and benefits. Inducible nicotine production is just one of many traits that are altered after herbivore attack, and the cost–benefit model provides a valuable heuristic framework in which to understand the selective factors responsible for the maintenance of inducibly expressed traits.

Keywords: Phenotypic plasticity; induced defense; nicotine; costs and benefits; post-fire germination


From Chemical to Population Ecology: Infochemical Use in an Evolutionary Context by Louise E. M. Vet (pp. 31-49).
The marriage of chemistry with ecology has been a productive one, providing a wealth of examples of how chemicals play important roles in the loves and lives of living organisms. At first the marriage may have been a simple and monogamous one with the major scientific aim of making proximate analyses of chemically mediated, individual level interactions. But times have changed and chemical ecology is broadening, embracing different approaches and disciplines. There is, for example, increasing appreciation of variability in the systems under study and an increase in evolutionary thinking. Another promising development is greater recognition of the potential importance of chemically mediated interactions for population dynamics and for structuring communities and species coexistence. The latter is an utterly underexplored area in chemical ecology. The field of chemical ecology of insect parasitoids shows some of these promising developments. Responses of parasitoids to infochemicals are increasingly studied with an integrated approach of mechanism and function. This integration of “how” and “why” questions significantly enhances the evolutionary and ecological understanding of stimulus–response patterns. The future challenge in chemical ecology is to demonstrate how chemically mediated interactions steer ecological and evolutionary processes at all levels of ecological organization. To reach this goal there is a need for interdisciplinary collaboration among chemists and ecologists working at different levels of organization and with different approaches, with other disciplines as partners.

Keywords: Chemical ecology; evolution; variation; population dynamics; community; species interactions; infochemical; semiochemical; parasitoid; foraging behavior; learning; phenotypic plasticity


Electrophysiologically and Behaviorally Active Volatiles of Buffalo Gourd Root Powder for Corn Rootworm Beetles by Allard A. Cossé; Thomas C. Baker (pp. 51-66).
The dried, powdered roots of buffalo gourd, Cucurbita foetidissima, were tested in a cornfield and shown to attract adult northern and southern corn rootworm beetles. Coupled gas chromatography–electroantennography (GC-EAG) analyses of headspace samples of the root powder showed several GC-EAG-active compounds on the antennae of female northern, southern, and western corn rootworms. Among other techniques, solid-phase microextraction and GC-mass spectrometry identified the following GC-EAG-active compounds: hexanol, nonanal, 1-octen-3-ol, benzaldehyde, benzyl alcohol, (E)-3-octen-2-one, (E,E)-3,5-octadien-2-one, and (E,Z)-3,5-octadien-2-one. EAG dose–response studies of several of the identified root powder volatiles also were performed and compared with results from known attractants. Field tests of synthetic root powder volatiles in commercial cornfields showed that northern corn rootworm adults were attracted to (E,E)-3,5-octadien-2-one. The antennae of the Diabrotica species and the field tests showed specificity for different geometrical isomers of 3,5-octadien-2-one, with a behavioral preference for (E,E)-3,5-octadien-2-one. In addition, we have shown that the efficacy of buffalo gourd root powder as a feeding stimulant and arrestant can be enhanced for northern and western corn rootworm adults by augmenting buffalo gourd root powder with additional (E,E)-3,5-octadien-2-one.

Keywords: Coleoptera; Chrysomelidae; buffalo gourd root powder; Cucurbita foetidissima ; Diabrotica virgifera virgifera ; D. undecimpunctata howardi ; D. barberi ; attractants; solid-phase microextraction; gas chromatography–electroantennography


Patterns of Oviposition Stimulants for Carrot Fly in Leaves of Various Host Plants by Thomas Degen; Hans-Ruedi Buser; Erich Städler (pp. 67-87).
Undamaged leaves of 12 host-plant species differing widely in acceptability to ovipositing carrot flies were extracted with a microwave-assisted method with hexane as solvent. The highly stimulatory diethyl ether fraction obtained by separation on a silica gel column was semiquantitatively analyzed by GC-MS for previously identified oviposition stimulants of the carrot fly (phenylpropenes, fluranocoumarins, polyacetylenes). Various plant species exhibited widely differing profiles of these compounds. In choice assays, moderate numbers of eggs were deposited underneath surrogate leaves sprayed with fractions that contained high amounts of just one type of compound and low amounts of the other two types. Only fractions with medium to high levels of at least two compound classes elicited strong ovipositional responses (e.g., phenylpropenes and polyacetylenes in Daucus carota, furanocoumarins and polyacetylenes in Heracleum sphondylium and Conium maculatum). None of the examined plants contained high quantities of all three compound classes. The contents of the stimulants seemed to account in a synergistic manner for the variation in activity of the diethyl ether fraction. However, they could not explain adequately the observed preference hierarchy of the carrot fly for the host-plant species.

Keywords: Phenylpropenes; furanocoumarins; polyacetylenes; coumarins; Apiaceae; trans-methylisoeugenol; trans-asarone; xanthotoxin; bergapten; falcarinol; falcarindiol; Psila rosae ; Diptera; Psilidae


Extracting Oviposition Stimulants for Carrot Fly from Host-Plant Leaves by Thomas Degen; Guy Poppy; Erich Städler (pp. 89-104).
Extracts of carrot foliage obtained with various extraction methods were compared for effectiveness in stimulating oviposition in the carrot fly. In choice assays, surrogate leaves treated with a hexane surface extract produced with a new microwave-assisted procedure were almost as acceptable as real host leaves. The high stimulatory activity of this extract was attributable to the raised solvent temperature, since cold hexane extracts were much less stimulatory. The microwave extract elicited about twice as much oviposition as the previously used dichloromethane surface extracts and the diethyl ether fraction of an extract that was obtained by brief immersion of leaves into water near its boiling point. The ovipositional responses to crude methanol and hot water extracts were weak because of the presence of yet unidentified polar deterrent compounds. Total extracts of ground foliage (vacuum distillation and extraction with liquid carbon dioxide) had no net stimulatory effect on oviposition.

Keywords: Psila rosae ; Diptera; Psilidae; Daucus carota ; Heracleum sphondylium ; Apiaceae; microwave-assisted extraction; leaf surface extracts; oviposition stimulants; oviposition deterrents


Identification of Female Sex Pheromone of the Legume Pod Borer, Maruca vitrata and Antagonistic Effects of Geometrical Isomers by Tarô Adati; Sadahiro Tatsuki (pp. 105-115).
An EAD-active component in a female abdominal tip extract of the legume pod borer, Maruca vitrata (Fabricius) (= M. testulalis), was identified as (E,E)-10,12-hexadecadienal (E10,E12–16:Ald). In laboratory bioassays, the purified synthetic E10,E12–16:Ald with 99% isomeric purity had attractancy to male moths equal to the crude extract. However, the unpurified chemical with 92% isomeric purity did not show any attractancy. Addition of 0.1 ng EZ isomer or 1 ng of EZ, ZE, or ZZ isomers of 10,12–16: Ald to 1 ng of the purified synthetic pheromone antagonized its attractancy as did addition of each isomer to 1 female equivalent of the crude extract. These results suggest that it is necessary to develop formulation and release techniques that maintain extremely high isomeric purity of the synthetic pheromone for male trapping in the field.

Keywords: Sex pheromone; legume pod borer; Maruca vitrata ; Pyralidae; Lepidoptera (E,E)-10,12-hexadecadienal; attraction; geometrical isomer; isomeric purity; antagonistic effect


Predicting Atmospheric Concentration of Pheromone in Treated Apple Orchards by D. M. Suckling; S. R. Green; A. R. Gibb; G. Karg (pp. 117-139).
A Lagrangian model was developed to predict the vertical distribution of pheromone in apple orchards treated with synthetic pheromone released from polyethylene tubing dispensers. Measurements of tree dimensions' dispenser heights, air temperature, and wind speed were used as inputs to the model. Data to test the model output were obtained by air sampling and capillary gas chromatography to determine atmospheric pheromone concentration. The model predicted highest concentrations of pheromone in the plane of the dispensers. Predicted and measured concentrations were in the range 0.5–5 ng/m3 for blocks treated with 1000 or 2000 dispensers/ha. Mean wind speed had a large influence on pheromone concentrations within the canopy with concentrations decreasing at higher wind speeds. Wind speeds <0.1 m/sec, which represent good flying conditions for moths, resulted in high levels of mean pheromone concentration. Dispenser height had only a small influence on the maximum pheromone concentration, with the peak concentrations decreasing with increasing application height. The lower peak concentration for an elevated dispenser occurred mainly because wind speeds were higher in the upper parts of the tree canopy. Air temperature, dispenser density, and pheromone release rate (as inferred by dispenser liquid length), also had a significant influence on pheromone concentration because of the linear relationship between these parameters and the corresponding flux of pheromone released into the treated orchards. We use known scaling relationships to demonstrate these effects.

Keywords: Pheromone; mating disruption; Lagrangian model; atmospheric concentration; turbulence


Allelochemical Potential of Metopium brownei by Ana Luisa Anaya; Rachel Mata; Fausto Rivero-Cruz; Blanca Estela Hernández-Bautista; Daniel Chávez-Velasco; Arturo Gómez-Pompa (pp. 141-156).
Metopium brownei is a tree that grows in coastal tropical forests along the Gulf of Mexico and in the Yucatan Peninsula. This medicinal species produces a strongly irritant exudate, and sometimes forms pure populations favored by fire. The bioactivity of the aqueous leachates, organic extracts (leaves, bark, and wood), and mixtures of urushiols and flavonoids from M. brownei were evaluated on the growth of two plants: Amaranthus hypochondriacus and Echinochloa crusgalli, and four phytopathogenic fungi: Fusarium oxysporum, Helminthosporium sp., Alternaria sp., and Pythium sp. Alkylcatechols (urushiols) were isolated from an acetone extract of the bark. Dihydroquercetin and eriodictyol were isolated from the chloroform–methanol extract of the wood. In addition, masticadienoic acid was isolated from the leaves. The aqueous leachates, organic extracts, and the mixtures of flavonoids and urushiols were inhibitory to the growth of test plants and phytopathogenic fungi. The allelochemical role of the bioactive compounds from M. brownei is discussed in relation with other results reported in some studies on Anacardiaceae family and M. brownei.

Keywords: Metopium brownei ; Anacardiaceae; dihydroquercetin; eriodyctiol; masticadienoic acid; urushiols; alkylcatechols; allelochemicals; allelopathics


Fragrance Collection, Storage, and Accumulation by Individual Male Orchid Bees by T. Eltz; W. M. Whitten; D. W. Roubik; K. E. Linsenmair (pp. 157-176).
Individually marked males of two species of Euglossa were sighted repeatedly and over considerable periods of time (up to 44 days) at artificial fragrance baits exposed on Barro Colorado Island (BCI), Panama. Individuals switched between different bait chemicals that are attractive for the respective species, and no bait preferences or individual bait constancy was observed. GC-MS analyses of 153 males of three species showed that individual hind tibiae contain highly variable quantities of a complex and species-specific blend of fragrance compounds, mainly terpenoids and aromatics. In all three species, frequency distributions of individual quantities were strongly skewed towards individuals with small amounts, and individual amount and complexity were positively correlated. Tibial contents of male Euglossa imperialis that were kept alive in a flight cage for 0, 5, 10, or 15 days showed no qualitative or quantitative change over time, suggesting that the fragrances are very efficiently stored in the hind legs. In Euglossa cognata wing wear, an established age correlate of the species, was positively correlated with individual fragrance quantity. Our results suggest that male euglossines forage continuously for a variety of volatiles, store them, and finally acquire large quantities of a complex and specific fragrance bouquet. Both qualitative and quantitative aspects of individual contents are likely to contain information on male phenotypic and genotypic quality.

Keywords: Euglossine bees; fragrance collection; sexual selection; species recognition; GC-MS


Comparative Study of Pheromone Production and Response in Swedish and Zimbabwean Populations of Turnip Moth, Agrotis segetum by Wenqi Wu; C. B. Cottrell; Bill S. Hansson; Christer Löfstedt (pp. 177-196).
Analysis of female sex pheromone gland extracts of the turnip moth (or common cutworm), Agrotis segetum, from Zimbabwe revealed three compounds previously identified as sex pheromone components in the Swedish population, namely (Z)-5-decenyl acetate (Z5–10:OAc), (Z)-7-dodecenyl acetate (Z7–12:OAc), and (Z)-9-tetradecenyl acetate (Z9–14:OAc). However, the proportions from the Zimbabwean population (1:0.25:0.03) differ from those in the Swedish population (1:5:2.5). In addition, gas chromatography–mass spectrometric (GC-MS) analysis of the Zimbabwean female gland extracts revealed a trace of (Z)-5-dodecenyl acetate (Z5–12:OAc). This compound has recently been identified as a fourth sex pheromone component for the Swedish population. Single-sensillum recordings from both Zimbabwean and Swedish populations showed the presence of two types of antennal receptors responding to either Z5–10:OAc or Z7–12:OAc. In Zimbabwean males the Z7–12:OAc receptor neuron appeared to be confined to the basal and medial thirds of the antennal branches, while in Swedish males it was distributed along the entire antennal branch. Dose–response curves of Z5–10:OAc or Z7–12:OAc specific receptor neurons from males of both populations showed similar response profiles, but the neurons of the Zimbabwean population showed higher maximal responses. In flight tunnel tests with Zimbabwean males, the three-component Zimbabwean blend of Z5–10:OAc, Z7–12:OAc and Z9–14:OAc elicited significantly greater responses than the Swedish blend, but not significantly greater than pheromone glands from calling Zimbabwean females. (Z)-5-decenol (Z5–10:OH), a constituent of gland extracts, exerted an antagonistic effect in the flight tunnel. In field tests conducted in Sweden, local males were preferentially attracted to local females, while in Zimbabwe preferential attraction to local females was less pronounced. Local response to the Swedish and Zimbabwean synthetic four-component blends mirrored the responses to the local females. Zimbabwean males are much more strongly attracted to Z5–10:OAc alone than are Swedish males and the high concentrations of Z7–12:OAc and/or Z9–14:OAc present in the Swedish blend reduced attraction of Zimbabwean males. This reduced attraction appears to be counteracted by the trace amounts of Z5–12:OAc found in the Swedish four-component blend. Addition of Z5–12:OAc to the three-component Zimbabwean blend did not, however, significantly increase the trap catches of Zimbabwean males.

Keywords: Sex pheromone; turnip moth; common cutworm; Agrotis segetum ; geographical population variation; receptor neurons; single-sensillum recordings; dose–response; flight tunnel; field tests


Discrimination Between Self-Produced Pheromones and Those Produced by Individuals of the Same Sex in the Lizard Cordylus cordylus by William E. Cooper Jr.; Johannes H. Van Wyk; P. Le F. N. Mouton (pp. 197-208).
Male and female Cordylus cordylus can discriminate between tiles labeled by their own pheromones and tiles labeled by individuals of the same sex, as shown by elevated tongue-flick rates in which the tongue contacts only air above the tiles labeled by other individuals and tongue-flicks in which the tongue contacts the tiles themselves. Potential pheromone sources for these discriminations are the femoral glands, cloacal glands, generation glands, ventral skin, and excretory products. Although studied in few species, pheromonal discriminations between self and other individuals, familiar and unfamiliar individuals, and kin and unrelated individuals appear to be broadly distributed in lizards, occurring in Iguania and in both Gekkonoidea and Scincomorpha within Scleroglossa. Both sexes of C. cordylus defend territories against both sexes. An ability to distinguish pheromones of other individuals of the same sex from self-produced pheromones would allow detection of intruders, but pheromonal discriminations among individuals would be more useful. Adaptive functions of pheromonal discriminations for residents and nonresidents and discriminatory abilities required are discussed. Tongue-flicks touching labeled tiles differed between experimental conditions, suggesting vomerolfactory discrimination, but the interpretation of a similar difference for tongue-flicks that contacted no substrate is problematical. Such air tongue-flicks might indicate sampling of volatile molecules for delivery to the vomeronasal organs. Experiments are needed to conclusively determine the sensory bases of the discriminations and the role of air tongue-flicks.

Keywords: Behavior; pheromone; self-recognition; tongue-flicking; Squamata; Cordylidae


Allelopathic Potential of Aquatic Plants Associated with Wild Rice (Zizania palustris): I. Bioassay with Plant and Lake Sediment Samples by H. A. Quayyum; A. U. Mallik; P. F. Lee (pp. 209-220).
The allelopathic potential of eight aquatic plants associated with wild rice was investigated using lettuce and wild rice seedling bioassays. Rhizome aqueous extracts of Scirpus acutus, Potamogeton natans, Nymphaea odorata, Nuphar variegatum; shoot extract of Eleocharis smallii; whole plant extract of Myriophyllum verticillatum; and leaf extract of P. natans significantly reduced the root length of lettuce and wild rice seedlings. The lettuce seedling bioassay was more sensitive than the wild rice bioassay. Shoot growth was less affected than the root growth. Water extract of sediments associated with the aquatic plants had little growth inhibitory effect on wild rice. Our study did not yield any conclusive evidence that the wild rice-associated aquatic plants have allelopathic effects on wild rice. We emphasize the use of target species as a bioassay material in allelopathic studies. Further investigation on allelopathic effects of lake sediments associated with the neighboring plants of wild rice is necessary to evaluate their ecological significance.

Keywords: Allelopathy; aquatic plants; growth inhibition; lake sediments; seedling bioassay; wild rice; Zizania palustris ; Eleocharis smallii ; Equisitum fluviatile ; Myriophyllum verticillatum ; Nuphar variegatum ; Nymphaea odorata ; Potamogeton natan ; Scirpus acutus ; Sparganium fluuctuans


Allelopathic Potential of Aquatic Plants Associated with Wild Rice: II. Isolation and Identification of Allelochemicals by H. A. Quayyum; A. U. Mallik; D. E. Orr; P. F. Lee (pp. 221-228).
Aqueous extracts of rhizomes of Scirpus acutus and shoots of Eleocharis smallii were analyzed for the presence of phytotoxic compounds using ethyl acetate extraction. The organic fractions of the extract of Scirpus rhizomes contained lactic, succinic, fumaric, 2-hydroxysuccinic, 2-phenyl lactic, m-hydroxybenzoic, p-hydroxybenzoic, protocatechuic, dehydroabietic, and ferulic acids; p-hydroxybenzyl alcohol, p-hydroxyphenyl ethanol and catechin. The extract of Eleocharis shoots contained 4-methoxy phenol, benzofuran, benzene acetic acid, 1-hydroxy-5-methyl acetophenone, and 1,3,4-dimethoxyphenol ethanone identified by GC-Mass spectroscopy. The potential allelopathic effect of these compounds on wild rice under field conditions was discussed.

Keywords: Allelochemicals; Eleocharis smallii ; plant phenolics; Scirpus acutus ; wild rice; Zizania palustris


Identification of Host-Related Volatiles Attractive to Pineapple Beetle Carpophilus humeralis by Bruce W. Zilkowski; Robert J. Bartelt; Daniel Blumberg; David G. James; David K. Weaver (pp. 229-252).
Volatiles collected from oranges fed upon by Carpophilus humeralis of either sex were consistently more attractive than volatiles from beetle-free oranges in wind-tunnel bioassays. Three compounds were identified as attractants from this system: 4-ethyl-2-methoxyphenol (1), 2,5-diisopropylpyrazine (2) (a new natural product), and 2-phenylethanol (3). Identifications were confirmed with synthetic compounds that had matching chromatographic and spectral properties. Compounds 1, 2, and 3 had only slight activity alone, but were highly synergistic with each other and with propyl acetate (PA), a fruity ester that is mildly attractive to Carpophilus beetles. Compound 2 was the most active in the wind tunnel; its threshold dose was 0.5 ng when PA was present. The structural specificity for these compounds was high. Twelve phenol analogs of 1 were tested, but only one of these, 2-methoxyphenol, was more attractive than the control. Similarly, the analogs of 2, 2-isopropylpyrazine and 2,6-diisopropylpyrazine, were completely inactive. In the field, a combination of 1, 2, and 3 was not attractive by itself, but it strongly synergized attraction to fermentation volatiles, Carpophilus pheromones, or both. Compounds 1, 2, and 3 apparently have a microbial origin because all three were detected when the host fruit was pineapples instead of oranges, because they could occur in the absence of beetles, and because autoclaved pineapple began to produce the compounds after inoculation from an attractive piece of fruit. The study demonstrated that host location for this generalist species can be far more complex than responding simply to the bouquet of low-molecular-weight volatiles normally associated with fermentation.

Keywords: Carpophilus humeralis ; 4-ethyl-2-methoxyphenol; 2,5-diisopropylpyrazine; 2-phenylethanol; microbe produced attractants; synergism; structure–activity relationship; field trials

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