Showing papers in "Journal of Chemical Ecology in 1995"

Foliar oxidative stress and insect herbivory: Primary compounds, secondary metabolites, and reactive oxygen species as components of induced resistance.

Abstract: Oxidative responses of plants to pathogens and other environmental stresses have received considerable recent attention. We propose that an oxidative response also occurs following attack by herbivores. Our data strongly indicate a shift in the oxidative status of soybean following herbivory by the insectHelicoverpa zea. Herbivory caused significant increases in lipid peroxidation and ·OH radical formation. The activity of several oxidative enzymes including lipoxygenases, peroxidase, diamine oxidase, ascorbate oxidase, and NADH oxidase I increased after herbivory on soybean. The enhanced production of phenolic compounds is indicated by an increase in the activity of phenylalanine ammonia lyase in wounded tissues. On the other hand, the level of soybean foliar antioxidants such as ascorbic acid, total carotenoids, nonprotein thiols, and catalase decreased significantly following herbivory. These results implicate primary compounds (e.g., ascorbic acid, proteins), secondary metabolites (e.g., phenolics), and reactive oxygen species (e.g., hydroxyl radical, hydrogen peroxide) as multiple components of induced resistance. The oxidative changes in the host plant correspond with increased oxidative damage in the midgut of insects feeding on previously wounded plants. Decreases in nonprotein thiols and reduced ascorbic acid occurred in midgut epithelial tissue from insects feeding on wounded plants compared to the insects on control plants. In contrast, midgut hydroperoxides and dehydroascorbic acid concentrations were greater in insects on wounded plants compared to their counterparts on control plants. We conclude that oxidative responses in soybean may have both positive and negative effects upon the host plant: a decrease in herbivory and an increase in oxidative damage to the plant. The salient benefit to the plant, in terms of insect resistance, is the relative balance between these opposing effects.

Volatiles emitted by different cotton varieties damaged by feeding beet armyworm larvae.

Abstract: Volatile compounds elicited by insect herbivore feeding damage in five cotton cultivars and one naturalized cotton variety were examined by allowing beet armyworm larvae to feed overnight on leaves and collecting volatiles from the plants in situ. Of 23 compounds identified from larval damaged leaves, terpenes and lipoxygenase-hydroperoxide lyase-derived volatiles predominated. No pronounced differences in the levels of volatile emission were noted from leaves of undamaged plants of the different varieties. However, average volatile emission from damaged leaves of the naturalized variety was almost sevenfold higher than from damaged leaves of the commercial cultivars. This was despite the fact that larvae preferred feeding on the leaves of commercial cultivars over those of the naturalized variety in choice tests.

Developmental stage of herbivore Pseudaletia separata affects production of herbivore-induced synomone by corn plants.

Abstract: The female parasitic waspCotesia kariyai discriminated between the volatiles of corn leaves infested by younger host larvaePseudaletia separata (first to fourth instar) and uninfested leaves in a Y-tube olfactometer; the wasps were attracted to the infested leaves. In contrast, when corn plants were infested by the later stages (fifth and sixth instar) of the armyworm, the wasps did not distinguish between infested corn leaves and uninfested corn leaves in the olfactometer. Mechanically damaged leaves were no more attractive than undamaged leaves, and host larvae or their feces were not attractive to the parasitoid. Through chemical analysis, the herbivore-induced plant volatiles were identified in the headspace of infested corn leaves. The herbivore-induced volatiles (HIVs) constituted a larger proportion of the headspace of corn leaves infested by early instar armyworms than of corn leaves infested by late instar armyworms. Application of third-instar larval regurgitant onto artificially damaged sites of leaves resulted in emission of parasitoid attractants from the leaf, whereas leaves treated with sixth-instar regurgitant did not. The function of this herbivore-stage related specificity of herbivore-induced synomones is discussed in a tritrophic context.

Effects of benzoic and cinnamic acids on membrane permeability of soybean roots.

Abstract: Benzoic (BEN) and cinnamic (CIN) acids are commonly found in soils and are considered as strong allelochemicals. Published information suggest that BEN and CIN and other phenolic acids decrease plant growth in part by suppressing nutrient absorption. However, studies on the mechanism of action were not conclusive. We examined the effects of BEN and CIN on the cell plasma membrane in intact soybean (Glycine max L. cv. Maple Bell) seedlings. Treating intact root systems with BEN or CIN rapidly increased electrolyte leakage and ultraviolet absorption of materials into the surrounding solution. After 12 hr of treatment, BEN and CIN lowered the extracellular sulfhydryl group content in roots. The two allelochemicals induced lipid peroxidation, which resulted from free radical formation in plasma membranes, inhibition of catalase and peroxidase activities, and sulfhydryl group depletion. Oxidation or cross-linking of plasma membrane sulfhydryl groups is the first mode of action of both compounds. The BEN- and CIN-induced decrease in soybean nutrient absorption may be a consequence of damage to cell membrane integrity caused by a decrease in sulfhydryl groups followed by lipid peroxidation.

Turnabout is fair play: Secondary roles for primary compounds.

Abstract: Chemically based resistance of plants to herbivorous insects is today essentially synonymous with allelochemically based resistance; the importance of plant secondary compounds in determining patterns of host-plant utilization has been established in a wide variety of insect-plant interactions. In contrast, primary metabolites, those involved in fundamental plant physiological processes, are rarely considered to be major determinants of host-plant resistance despite the fact that, as insect nutrients, they can have profound effects on behavior and physiology. The degree to which variation in plant primary metabolism results from the selective impact of herbivory may be greatly underestimated in that the biosynthetic and structural diversity of primary metabolites and the consequences of that diversity on herbivores are rarely taken into account in most studies of insect preference and performance. Qualitative and quantitative variation in the production of primary metabolites can result from herbivore selection pressure if production of primary metabolites is under genetic control and if plant fitness in the presence of herbivores is associated in a predictable way with genetically based primary metabolite variation. Variation in primary metabolism is likely to be particularly effective as a defense against highly oligophagous herbivores with limited mobility, especially those confined to structures containing allelochemicals that could neutralize the benefits associated with compensatory feeding.

Insecticidal defenses of Piperaceae from the neotropics.

Abstract: Insecticidal and growth-reducing properties of extracts of 14 species of American neotropical Piperaceae were investigated by inclusion in diets of a polyphagous lepidopteran, the European corn borer,Ostrinia nubilalis. Nutritional indices suggested most extracts acted by postdigestive toxicity.Piper aduncum, P. tuberculatum, andP. decurrens were among the most active species and were subjected to bioassay-guided isolation of the active components. Dillapiol was isolated from the active fraction ofP. aduncum, piperlonguminine was isolated fromP. tuberculatum, and a novel neolignan fromP. decurrens. The results support other studies on Asian and AfricanPiper species, which suggest that lignans and isobutyl amides are the active defence compounds in this family.

Hydrocarbon dynamics within and between nestmates inCataglyphis niger (Hymenoptera: Formicidae)

Abstract: The objective of the present study was to evaluate the interrelationship between the cuticular and postpharyngeal glands' hydrocarbons, both in the individual ant and during its interaction with nestmates. In vivo radiochemical assays were employed to monitor the de novo hydrocarbon biosynthesis from acetate in the ant's body. The newly synthesized hydrocarbons appeared first internally and after 24 hr they accumulated in the postpharyngeal gland and on the cuticular surface. Blocking the possibility of external transfer of hydrocarbons between cuticle and postpharyngeal gland led to a significant decrease of labeled hydrocarbons in the postpharyngeal gland. In addition, during encounters between labeled and unlabeled ants, newly synthesized hydrocarbons were transferred, mainly via trophallaxis, but also by allo-grooming and physical contact. In view of these results, we propose as a model for their dynamics that hydrocarbons are synthesized in tissues associated with the integument. Through self-grooming, there is a constant exchange of hydrocarbons between the cuticular surface and the postpharyngeal gland. Furthermore, in encounters between nestmates, hydrocarbons are exchanged among them mostly by trophallaxis, with the mediation of the postpharyngeal gland. Thus, this gland acts as a pool for mixing colonial hydrocarbons and may serve to attain a unified colony odor.

The raison d'etre of pyrrolizidine alkaloids in Cynoglossum officinale: Deterrent effects against generalist herbivores

Abstract: In this study we tested whether pyrrolizidine alkaloids (PAs) ofCynoglossum officinale serve as antifeedants against herbivores. Total PA N-oxide extracts of the leaves significantly deterred feeding by generalist herbivores. Specialist herbivores did not discriminate between food with high and low PA levels. Three PAs fromC. officinale, heliosupine, echinatine, and 3′-acetylechinatine, equally deterred feeding by the polyphagous larvae ofSpodoptera exigua. Although the plants mainly contain PAs in their N-oxide form, reduced PAs deterred feeding byS. exigua more efficiently than PA N-oxides. On rosette plants, the monophagous weevilMogulones cruciger significantly consumed more of the youngest leaves, which had the highest PA level and the highest nitrogen percentage. Larvae ofEthmia bipunctella, which are oligophagous within the Boraginaceae, did not discriminate between leaves. All generalist herbivores tested significantly avoided the youngest leaves with the highest PA levels. In the field, the oldest leaves also were relatively more damaged by herbivores than the youngest leaves. It is hypothesized that the skewed distribution of PAs over the leaves of rosette plants reflects optimal defense distribution within the plant.

Volatile compounds induced by herbivory act as aggregation kairomones for the Japanese beetle (Popillia japonica Newman).

Abstract: The Japanese beetle is a polyphagous insect that typically aggregates on preferred host plants in the field. We studied the response of Japanese beetles to artificial damage, fresh feeding damage, and overnight feeding damage to test the hypothesis that beetles are attracted to feeding-induced volatiles. Crabapple leaves that had been damaged overnight by Japanese beetles or fall webworms attracted significantly more Japanese beetles than did undamaged leaves. Artificially damaged leaves or leaves freshly damaged by Japanese beetles, however, were not significantly more attractive than undamaged leaves. Leaves that had been damaged overnight by Japanese beetles or fall webworms produced a complex mixture of aliphatic compounds, phenylpropanoid-derived compounds, and terpenoids. In comparison, artificially damaged leaves or leaves with fresh Japanese beetle feeding damage generated a less complex blend of volatiles, mainly consisting of green-leaf odors. Feeding-induced odors may facilitate host location and/or mate finding by the Japanese beetle.

Multifunctional communication inRiptortus clavatus (Heteroptera: Alydidae): Conspecific nymphs and egg parasitoidOoencyrtus nezarae use the same adult attractant pheromone as chemical cue

Abstract: The bean bug,Riptortus clavatus lays scattered eggs (as opposed to the egg masses of pentatomids) on host as well as nonhost plants. Therefore, the first feeding stage (second-instar) nymphs emerging from eggs laid on nonhost plants need a signal that enables them to locate a food source at the lowest energy cost. Male-released (E)-2-hexenyl (E)-2-hexenoate, (E)-2-hexenyl (Z)-3-hexenoate, and myristyl isobutyrate play the double role of attractant pheromone for adults as well as aggregation pheromone, which enables the second-instar nymphs to find the host food plant. These male-specific semiochemicals are released only when foodstuff is available. On the other hand, females ofOoencyrtus nezarae, the most effective parasitoid of the host in Kumamoto, Japan (where the field experiments were conducted), utilize these semiochemicals as kairomones in order to locate the potential host community. Field experiments revealed that the synthetic pheromone rivaled 10 live males in the attraction of adults and second-instar nymphs. Captures of the egg parasitoidO. nezarae females in cylindrical sticky traps were significantly higher in traps baited with the synthetic semiochemicals than in control traps. The number of females captured was significantly higher than the number of males, although the captures in the sticky suction trap system revealed that the populations of male and female were not significantly different.

Comparison of three methods for quantifying brown algal polyphenolic compounds.

Abstract: Three methods of quantifying total phenolic compounds in marine brown algae were compared for their ability to measure accurately known concentrations of phloroglucinol in the presence of a protein, bovine serum albumin (BSA). These methods were: (1) a Folin-Ciocalteu assay for compounds dissolved in 80% methanol, (2) a Folin-Ciocalteu assay for compounds dissolved in 75% methanol-25% trichloroacetic acid, and (3) an assay in which polyvinylpolypyrrolidone (PVPP) was used to remove phenolic compounds in order to quantify nonphenolic, Folin-Ciocalteu-reactive materials. The Folin-Ciocalteu assay used with compounds dissolved in 80% methanol was the method that produced the most consistent results. It was also the assay in which the presence of proteins interfered least with the measurements of phloroglucinol and the assay that was easiest to conduct. The presence of TCA decreased the pH of the extracting solution and increased the amounts of proteins in solution. These proteins later interfered with the Folin-Ciocalteu reaction. TCA effectively bound proteins when protein concentrations were low but not when protein concentrations were high. The amount of phloroglucinol removed by PVPP varied widely and was dependent on phloroglucinol concentration, making this an unreliable method for quantifying phenolic concentrations. The Folin-Ciocalteu assay will measure some nonphenolic substances when brown algae are extracted in 80% methanol; however, inFucus gardneri, nonphenolic substances were at most 5% of the material quantified by the assay.

Consequences of biotransformation of plant secondary metabolites on acid-base metabolism in mammals—A final common pathway?

Abstract: Regulation of acid-base homeostasis is essential for mammals and birds. Biotransformation and metabolism of absorbed plant secondary metabolites (PSMs) results in the production of organic acids that threaten acid-base homeostasis. Consequently these acids must be buffered and excreted from the body. The production of an acid load from detoxified PSMs should occur in herbivorous mammals and birds and with most PSMs and so may provide a unifying theme to explain many effects of PSMs on animal metabolism. Since the organic acids will be largely ionized at physiological pH, disposal of the hydrogen ion and the organic anion may proceed independently. Most hydrogen ions (H+) from organic acids are eliminated by one or more of three ways: (1) when they react with bicarbonate in the extracellular fluid to form carbon dioxide and the carbon dioxide is exhaled, (2) when they bind to dibasic phosphate and are excreted by the kidney as monobasic phosphate, and (3) when they are buffered and retained in the skeletal system. The secretion of phosphate ions and ammonium excretion are two ways in which the kidney replaces bicarbonate ions that have been eliminated as carbon dioxide. Secretion in the kidney tubule is an important means of excreting excessive organic anions rapidly. This process is saturable and may be subject to competition from a variety of different metabolites. Lagomorphs have limited capacity to form new bicarbonate from ammonium excretion and may therefore be obliged to excrete other cations such as sodium to balance the excretion of organic anions from PSMs. Acidemia has wide-ranging impacts on animals but browsing mammals and birds may have to break down muscle tissues to provide for urinary ammonium in order to generate bicarbonate for buffering. Acidemia also can affect the extent of urea recycling. Animals consuming browse diets may have to regulate feeding so that the rate of formation of hydrogen ions does not exceed the rate of disposal. The mechanisms by which this could occur are unknown.

Effects of biotic and abiotic stress on induced accumulation of terpenes and phenolics in red pines inoculated with bark beetle-vectored fungus

Abstract: This study characterized the chemical response of healthy red pine to artificial inoculation with the bark beetle-vectored fungusLeptographium terebrantis. In addition, we sought to determine whether stress altered this induced response and to understand the implications of these interactions to the study of decline diseases. Twenty-five-year-old trees responded to mechanical wounding or inoculation withL. terebrantis by producing resinous reaction lesions in the phloem. Aseptically wounded and wound-inoculated phloem contained higher concentrations of phenolics than did constitutive tissue. Trees inoculated withL. terebrantis also contained higher concentrations of six monoterpenes,α-pinene,β-pinene, 3-carene, limonene, camphene, and myrcene, and higher total monoterpenes than did trees that were mechanically wounded or left unwounded. Concentrations of these monoterpenes increased with time after inoculation. Total phenolic concentrations in unwounded stem tissue did not differ between healthy and root-diseased trees. Likewise, constitutive monoterpene concentrations in stem phloem were similar between healthy and root-diseased trees. However, when stem phloem tissue was challenged with fungal inoculations, reaction tissue from root-diseased trees contained lower concentrations ofα-pinene, the predominant monoterpene in red pine, than did reaction tissue from healthy trees. Seedlings stressed by exposure to low light levels exhibited less extensive induced chemical changes when challenge inoculated withL. terebrantis than did seedlings growing under higher light. Stem phloem tissue in these seedlings contained lower concentrations ofα-pinene than did nonstressed seedlings also challenge inoculated withL. terebrantis. It is hypothesized that monoterpenes and phenolics play a role in the defensive response of red pine against insect-fungal attack, that stress may predispose red pine to attack by insect-fungal complexes, and that such interactions are involved in red pine decline disease. Implications to plant defense theory and interactions among multiple stress agents in forest decline are discussed.

Antennal perception of oilseed rape,Brassica napus (Brassicaceae), volatiles by the cabbage seed weevilCeutorhynchus assimilis (Coleoptera, Curculionidae).

Abstract: The response of theCeutorhynchus assimilis antenna to volatiles in air entrainment-derived extracts of oilseed rape,Brassica napus, was studied using coupled gas chromatography (GC)-electroantennography (EAG) and coupled GC-single cell recording (SCR) By means of these techniques and coupled gas chromatography-mass spectrometry (GC-MS), 25 active compounds were identified, including isoprenoids and compounds derived from fatty acids and amino acids Some of the latter, the isothiocyanates and goitrin, and probably indole and benzyl cyanide, are catabolites of glucosinolates The electrophysiological activity of the identified compounds was confirmed by EAG using a physiologically discriminating dose, and by SCR studies The importance of the combined use of the EAG and SCR techniques was demonstrated, since specific olfactory cells were located for five compounds that did not elicit significant EAG responses The majority of the olfactory cells from which single cell recordings were obtained showed very high specificity, and in numerous recordings there were consistent pairings of specific cell types

A chemical basis for differential allelopathic potential of sorghum hybrids on wheat

Abstract: The basis for differential allelopathic potentials among sorghum (Sorghum bicolor L. Moench) hybrids was investigated by conducting quantitative and qualitative studies of their phenolic contents. Total phenolic content in sorghum plant parts varied within hybrids, among hybrids, and between growing seasons. Inhibition of wheat (Triticum aestivum L.) radicle growth was positively associated (r=0.66) with concentrations of total phenolics contained in plant parts. Extracts from culms contributed the higherst proportion of toxicity from sorghum plants, inhibiting radicle growth up to 74.7%. Concentrations of five phenolic acids,p-hydroxybenzoic (POH), vanillic (VAN), syringic (SYR),p-coumaric (PCO), and ferulic (FER), differed in all plant parts of the three sorghum hybrids. Concentrations of POH, VAN, and SYR were consistently higher than PCO and FER. PCO and FER wer absent from some plant parts, with FER being the most frequently missing. Inhibition of wheat radicle growth was found to be positively associated with the concentration of each phenolic acid. Vanillic acid was most highly associated (r=0.44) with inhition. Thus, above-ground sorghum tissues contained phenolic acids that contributed to allelopathic potential. Additionally, sorghum roots exuded POH, VAN, and SYR that may enhance the overall allelopathic potential of sorghum during growth and after harvest when residues remain on the soil surface or are incorporated prior to planting a subsquent crop.

Ontogenic development of chemical defense by seedling resin birch: Energy cost of defense production.

Abstract: Whether production of chemical defenses by plants is or is not an energetically costly process is an important, but unresolved, question in chemical ecology. We suggest studies of the ontogenetic development of plant defense systems can help resolve the question. As an example of this approach to the cost question, we explore the problems associated with production of immobile chemical defenses that defend juvenile resin birches against browsing by mammals. From this exploration we draw two conclusions: (1) Shortly after germination, production of chemical defenses by small-seeded species, such as birch, is energetically costly. (2) Opposing selection for defense versus competitive ability in the seedling stage of birch has resulted in a trade-off in allocation of carbon to production of immobile chemical defense versus allocation of carbon to production of storage reserves. We suggest this trade-off results in a large indirect cost of defense because carbon used for production of immobile chemical defenses is unavailable for support of growth in the future, but stored carbon can be used to support future growth.

Modeling metabolic costs of allelochemical ingestion by foraging herbivores

Abstract: A mathematical model of intermediary metabolism of allelochemicals by vertebrate herbivores is presented and used to quantify the metabolic costs of detoxification. Conjugation with glucuronic acid and maintenance of acid-base status causes catabolism of amino acid and is shown to result in loss of body protein and depletion of glucose. An interaction between allelochemical dose and nutrient status is found, and the ratio of allelochemical to nutrient absorption rate defines the tolerance of the animal to absorbable allelochemical concentration in foods. The interaction is nonlinear and the ecological implications of this for foraging behavior and diet choice are discussed.

Host microhabitat location by stem-borer parasitoid Cotesia flavipes: the role of herbivore volatiles and locally and systemically induced plant volatiles.

Abstract: The origin of olfactory stimuli involved in the host microhabitat location inCotesia flavipes, a parasitoid of stem-borer larvae, was investigated in a Y-tube olfactometer. The response of femaleC. flavipes towards different components of the plant-host complex, consisting of a maize plant infested with two or more larvae of the stem borerChilo partellus, was tested in dualchoice tests. The concealed lifestyle of the stem-borer larvae did not limit the emission of volatiles attractive to a parasitoid. A major source of the attractive volatiles from the plant-host complex was the stem-borer-injured stem, including the frass produced by the feeding larvae. Moreover, the production of volatiles attractive to a parasitoid was not restricted to the infested stem part but occurs systemically throughout the plant. The uninfested leaves of a stem-borer-infested plant were found to emit volatiles that attract femaleC. flavipes. We further demonstrate that an exogenous elicitor of this systemic plant response is situated in the regurgitate of a stem-borer larva. When a minor amount of regurgitate is inoculated into the stem of an uninfested plant, the leaves of the treated plant emit volatiles that attract femaleC. flavipes.

Salivary proline-rich proteins in mammals: Roles in oral homeostasis and counteracting dietary tannin.

Abstract: We review information on the structure of proline-rich proteins (PRPs), their various functions related to oral homeostasis and dietary tannin, and the structural basis of these functions. Consideration of the multifunctional nature of these salivary proteins helps explain both the subtle and large variations found in structure and secretion rates both within individuals and between species. We propose that the ancestral function of PRPs is in maintaining oral homeostasis and that counteracting dietary tannins by binding with them is a derived function. PRPs are effective in oral homeostasis at low secretion levels, whereas counteracting tannin depends on high secretion levels. In the dietary habits ranging from carnivores through omnivores to exclusively planteaters, the dietary nitrogen level is progressively reduced, and plant allelochemical intake, including tannins, increases. We suggest that during this evolution from meat-eater to plant-eater, there was some point in omnivory at which selective pressure from nitrogen limitations, arising from a low nitrogen/high tannin diet, became sufficiently great for the evolution of increased secretion level and diversification of PRPs for dealing with tannin. If this hypothesis is correct, carnivorous mammals should secrete low levels of PRPs for oral homeostasis, but should never secrete high levels, unless they are secondarily carnivorous. Omnivores consuming a diet of very little animal tissue but higher levels of tannin-containing foliage or fruit should generally have the capacity to produce high levels of salivary PRPs. Browsers and frugivores should also produce high levels of PRPs, but grazers may have reduced secretion rates depending on the antiquity of the dietary habit. This hypothesis is consistent with the limited information available on the abundance, type, and distribution of PRPs in mammals. Studies are suggested which would test the functional and evolutionary arguments presented.

Enantiomeric composition of ipsdienol: A chemotaxonomic character for north American populations ofIps spp. in thepini subgeneric group (coleoptera: Scolytidae)

Abstract: Thirty-five populations ofIps pini (Say) and one population each ofIps avulsus (Eichhoff) andIps bonanseai (Hopkins) were analyzed for the enantiomeric composition of ipsdienol (2-methyl-6-methylene-2,7-octadien-4-ol). Populations ofI. pini occur as at least two distinct regional pheromone variants: New York type [32%-(−) to 56%-(−)-ipsdienol] and California type [94%-(−) to 98%-(−)-ipsdienol]. A third phenotype may occur in southeastern British Columbia, Idaho, and Montana [91%-(−) to 95%-(−)], possibly indicating a zone of hybridization. Populations of the New York type occur in southwestern British Columbia, Alberta, Saskatchewan, Minnesota, and Wisconsin suggesting a continuum through the Canadian provinces and Lake States. The presence of the New York type in western Canada is likely linked to the Quaternary history of the transcontinentally distributed host,Pinus banksiana Lamb. MaleI. avulsus [∼25%-(−)] and maleI. bonanseai [−29%-(−)] both produce ipsdienol, but not ipsenol. Production of ipsdienol by maleI. pini was evaluated in six differentPinus spp. hosts. Following transfer of maleI. pini to hosts other than the host of origin, the percentage of the (−)-enantiomer of ipsdienol declined when compared to production in the host of origin.

Evaluation of organic infusions and synthetic compounds mediating oviposition in Aedes albopictus and Aedes aegypti (Diptera: Culicidae)

Abstract: Oviposition responses of gravidAedes albopictus andAe aegypti were evaluated to natural organic infusions (hay infusion, larval rearing water, and field-collected larval water) as well as compounds isolated from hay infusion (3-methylindole, 4-methylphenol, 4-ethylphenol, indole, and phenol) known to elicit oviposition inCulex mosquitoes In laboratory bioassays, significant oviposition responses were obtained fromAe albopictus, but not fromAe aegypti, to dilutions of hay infusion and field water Oviposition responses of both species were moderate to the synthetic compounds tested in the laboratory (001–100 µg/liter) Only 3-methylindole (01 µg/liter) and 4-ethylphenol (10 µg/liter) elicited significantly more oviposition byAe albopictus than did well water Of the synthetic compounds tested withAe aegypti, only phenol (10 µg/liter) and 4-ethylphenol (01 µg/liter) elicited significantly more oviposition than did well water Significant repellency or oviposition deterrence for both species occurred in response to at least one high concentration of most of the compounds tested In field cage evaluations, oviposition responses byAe albopictus were strongest to larval water and field water, moderate to hay infusion and 3-methylindole (100 µg/liter), and low to well water A mixture of five synthetic compounds mimicking hay infusion was no more effective than 3-methylindole alone ForAe aegypti, oviposition responses were greatest to larval water and least to 3-methylindole In an olfactometer, gravid females of both species oriented more to field water than to well water and onlyAe albopictus oriented more to larval water or hay infusion than well water In general, gravidAe albopictus responded more strongly to oviposition stimuli than didAe aegypti

Early warning in the predation sequence: A disturbance pheromone in Iowa darters (Etheostoma exile).

Abstract: The probability of prey avoiding a predator's attack should increase if the predator's presence is detected at an early stage in the predation sequence In this study, we tested whether threatened Iowa darters (Etheostoma exile) release disturbance pheromones that warn conspecifics of the presence of predation threat Pairs of aquaria were visually isolated from one another, but connected chemically by water circulating between them Darters in one aquarium were observed before and after darters in the other aquarium were chased with a model predator In control tests, the model was moved in the same manner but there were no darters in the upstream tank Darters receiving water from threatened fish increased vigilance behavior and decreased movement Vigilant fish raised their head above the substratum, propping themselves up on their pectoral fins and/or arching their neck dorsally, pointing the snout upward Exposure to water from disturbed darters suppressed exploratory behavior and resulted in movement by short rapid hops that ended abruptly in a rigid, alert posture This study suggests that Iowa darters release a disturbance pheromone that can provide conspecifics with an early warning of predation risk

Semiochemicals from bark beetles: New results, remarks, and reflections.

Abstract: A brief survey is given about recent results in the identification of semiochemicals in bark beetles: Males ofIps sexdentatus (Boern.), stressed by the attack on resinous trees produce large amounts of 3(S)-1-methyl-5-(1-hydroxyl-1-methylethyl)-cyclohexa-1,3-diene. The compound appears to be derived from Δ3-carene and acts as a repellent. Males ofIps typographus (L.), stressed through the attack on unsuitable host material release 3-methyl-7-methylene-1,3(E), 8-nonatriene, which seems to act as a repellent. The odor bouquet of three species ofPityogenes is described. The occurrence of (+)-grandisol and other compounds related to weevil pheromones points to a close relation between Scolytidae and Curculionidae. Females ofDendroctonus simplex (Le Conte) use (−)-frontalin as the main pheromone. 6-Methyl-6-hepten-2-one, a minor component among the volatile compounds released by the females, is regarded as a possible precursor of frontalin. Similarly, (2R,5S)-2(1-hydroxyl-1-methylethyl)-5-methyltetrahydrofuran, pityol, a pheromone ofPityophthorus spp., is regarded to at least share a common biogenetic precursor with 6-methyl-5-hepten-2-ol, sulcatol. A new bicylic acetal, 2-ethyl-1,5-dimethyl-6,8-dioxabicyclo[3.2.1]octane, is described as an aggregation pheromone of the beech bark beetle,Taphrorychus bicolor (Herbst). Structural relationships between bark beetle pheromones and plant volatiles are discussed.

Effects of fertility on biomass, phytotoxicity, and allelochemical content of cereal rye

Abstract: Studies were conducted to evaluate biomass production, tissue phytotoxicity, and allelochemical content of rye (Secale cereale L.) shoots grown in three fertility regimes (low, medium or high) in the greenhouse. Wheeler rye or a polyculture of rye and hairy vetch (Vicia villosa Roth) grown with high fertility produced the greatest biomass (78.7 and 82.7 g), with the lowest root-to-shoot ratio (0.22 and 0.43) produced in the high-fertility treatments. The polyculture treatment grown with low fertility had a greater proportion of hairy vetch (18%) than when grown with high fertility (6%). Rye shoot residue phototoxicity was affected by fertility regime. Radicle elongation of cress (Lepidium sativum L.) and barnyardgrass [Enchinochloa crus-galli (L.) Beauv. I was inhibited by rye shoot residues in a modified Parker bioassay. Rye shoot residue grown with low fertility was less inhibitory to cress radicle elongation than rye residue from the medium- or high-fertility regimes. Extracts of dried rye shoots grown with high fertility were less inhibitory than extracts from other fertility regimes. The concentrations of ether extracts of rye causing 50% inhibition (I50) of cress radicle elongation were between 125 and 276 µg/ml for greenhouse-grown and 60 and 138 µg/ml for the field-grown rye shoots. The major phytotoxic compounds in the rye shoot extracts were identified as DIBOA and BOA. The concentration of DIBOA in the greenhouse-grown rye shoots ranged between 128 and 423 µg/g while BOA concentration ranged between 2.5 and 31 µg/g. DIBOA and BOA levels were lowest in rye shoots grown with high fertility. Correlations between rye shoot biomass, DIBOA and BOA concentration, and cress barnyardgrass radicle length were significant.

Aggregation pheromone of coconut rhinoceros beetle,Oryctes rhinoceros (L.) (coleoptera: Scarabaeidae)

Abstract: Male coconut rhinoceros beetles,Oryctes rhinoceros (L.), produce three sex-specific compounds, ethyl 4-methyloctanoate, ethyl 4-methylheptanoate, and 4-methyloctanoic acid, the first of which is an aggregation pheromone. Synthesis of these compounds involving conjugate addition of organocuprates to ethyl acrylate is reported. In field trapping experiments, (4S)-ethyl 4-methyloctanoate and the racemic mixture were equally attractive and 10 times more effective in attracting beetles than ethyl chrysanthemumate, a previously recommended attractant. Ethyl 4-methylheptanoate was as attractive as ethyl chrysanthemumate and more attractive than 4-methyloctanoic acid, but further studies are required before it can be classed as an aggregation pheromone. Compared to ethyl 4-methyloctanoate alone, combinations of the three male-produced compounds did not increase attraction, whereas addition of freshly rotting oil palm fruit bunches to pheromone-baited traps significantly enhanced attraction. With increasing dose, captures ofO. rhinoceros increased, but doses of 6, 9, and 18 mg/day were competitive with 30 mg/day lures. Newly designed vane traps were more effective in capturing beetles than were barrier or pitfall traps. Results of this study indicate that there is potential for using ethyl 4-methyloctanoate in operational programs to controlO. rhinoceros in oil palm plantations.

Electroantennographic and coupled gas chromatographic-electroantennographic responses of the mediterranean fruit fly,Ceratitis capitata, to male-produced volatiles and mango odor.

Abstract: We have identified five compounds from the headspace of calling male Mediterranean fruit flies (medfly),Ceratitis capitata (Wiedemann), and three compounds from the headspace of ripe mango (Mangifera indica L). using coupled gas chromatographic-electroantennographic (GC-EAG) recordings, coupled gas chromatographic-mass spectrometric (GC-MS) analysis, and electroantennographic (EAG) assays of standards. The male-produced volatiles eliciting responses from female antennae were ethyl-(E)-3-octenoate, geranyl acetate, (E,E)-α-farnesene, linalool, and indole. An EAG dose-response test of linalool enantiomers and indole with female medfly antennae showed relatively strong EAG activities, but no significant difference between (R)-(-)-linalool and (S)-(+)-linalool. The three mango volatiles were identified as (1S)-(-)-β-pinene, ethyl octanoate, andβ-caryophyllene. In addition, a strong antennal response was recorded from a contaminant,α-copaene, present in a commercial sample ofβ-caryophyllene. The EAG response amplitudes from both male and female antennae to the above three mango volatiles were significantly greater than to a hexanol control. For both male and female medfly antennae, the greatest EAG responses were elicited byβ-caryophyllene followed by ethyl octanoate. The mean EAG responses of female antennae toβ-caryophyllene and (1S)-(-)-β-pinene were significantly greater than those of male antennae.

Role of volatile infochemicals emitted by feces of larvae in host-searching behavior of parasitoid Cotesia rubecula (Hymenoptera: Braconidae): a behavioral and chemical study.

Abstract: The role of volatile infochemicals emitted by feces of larvae in the host-searching behavior of the parasitoidCotesia rubecula was evaluated during single- and dual-choice tests inside a wind tunnel. The following treatments were tested: feces produced by second and fourth instars ofPieris rapae (preferred host), second instars ofP. brassicae (inferior host), second instars ofP. napi (nonhost), and wet feces of second instars ofP. rapae. During a single-choice situation females ofC. rubecula oriented to all types of feces tested. When a preference was to be made,C. rubecula preferred feces of second instars ofP. rapae over that of fourth, feces ofP. rapae over that ofP. brassicae, feces ofP. napi over that ofP. brassicae, and wet over normal host feces. No preference was exhibited between feces of second instars ofP. napi and that of second instars ofP. rapae. The relative importance of infochemicals from host feces versus plant damage caused by host larvae to the searching behavior ofC. rubecula was also evaluated. Plant damage was more important to the searching females than host feces when feces were present in specific concentrations in relation to damage. The volatiles released by normal and wet feces of second instars ofP. rapae, wet feces of fourth instars ofP. rapae, and normal and wet feces ofP. brassicae were collected and identified. Overall, 85 chemical compounds were recorded belonging to the following chemical groups: alcohols, ketones, aldehydes, esters, isothiocyanates, sulfides, nitriles, furanoids, terpenoids and pyridines. The blend of chemicals emitted by feces of different instars ofP. rapae and different species ofPieris exhibited an instar and species specificity in both quantity and quality. Wetting of normal feces increased the amount of volatile chemicals released, and it was also responsible for the appearance of new compounds. The role of feces of larvae in the host-seeking behavior ofC. rubecula is discussed.

Tracking variable environments : there is more than one kind of memory

Abstract: Three kinds of memory help herbivores track changes in the environment. The first is the collective memory of the species with genetic instructions that have been shaped by the environment through millennia. This includes skin and gut defense systems. Auditory and visual stimuli and sensations of pain impinge upon the skin defense system that evolved in response to predation. The taste of food and the sensations of nausea and satiety are an integral part of the gut defense system that evolved in response to toxins and nutrients in plants. The second kind of memory in social mammals is represented by the mother, a source of transgenerational knowledge, who increases efficiency and reduces risk of learning about foods and environments. The third kind of memory is acquired by individual experience. Postingestive feedback from nutrients and toxins enables individuals to experience the consequences of food ingestion and to adjust food preference and selection commensurate with a food's utility. The three memories interact, each linking the past to the present, and collectively shape the present and future of every individual. Thus, the dynamics of foraging involves appreciating the uniqueness of individuals and subgroups of animals, each with their own genetic and behavioral history, and recognizing that foraging behaviors may not be stable, optimal, or even predictable in the conventional sense.

Secondary chemistry of hybrid and parental willows: Phenolic glycosides and condensed tannins in Salix sericea, S. eriocephala , and their hybrids

Abstract: Salix sericea andS. eriocephala differ markedly in secondary chemistry.S. sericea produces phenolic glycosides, salicortin and 2′-cinnamoylsalicortin, and low concentrations of condensed tannin. In contrast,S. eriocephala produces no phenolic glycosides, but high concentrations of condensed tannins. Hybrid chemistry is intermediate for both types of chemicals, suggesting predominantly additive inheritance of these two defensive chemical systems from the parental species. However, there is extensive variation among hybrids. This variation may be due to genetic variation among parental genotypes, which genes were passed on, or to subsequent back-crossing. The differences in chemistry are likely to exert a strong effect on the relative susceptibility of hybrid and parental willows to herbivores.

Alkadienes mediating courtship in the parasitoidCardiochiles nigriceps (Hymenoptera: Braconidae).

Abstract: Courtship inCardiochiles nigriceps (Viereck) (Hymenoptera: Braconidae) involves male attraction to females and male antennation of females followed by mounting and copulation. Once the female is located, antennation and mounting of the female are mediated by the hydrocarbon fraction of female's Dufour's gland and cuticle. The identification of the cuticular hydrocarbons of males and females revealed a mixture of alkanes and alkenes, in addition to a series of alkadienes specific to females. These female-specific alkadienes reported from Braconidae are unusual among insect alkadienes in that the second double bond occurs in the middle of the molecule. Bioassays with three available alkadienes revealed that contact behaviors (antennation and mounting) are in part mediated by the (Z,Z)-7, 13-heptacosadiene and at least one other alkadiene in combination with other hydrocarbons found in males and females.