Showing papers in "Chemoecology in 1998"
TL;DR: It is proposed that variation in the responses of carbon-based secondary compounds to fertilization in woody plants has a biosynthetic cause and accelerated plant growth induced by fertilization may cause a reduction in concentrations of phenylpropanoids but may affect less or not at all the levels of other classes of secondary compounds.
Abstract: We propose that variation in the responses of carbon-based secondary compounds to fertilization in woody plants has a biosynthetic cause. The synthesis of phenylpropanoids and derived compounds (e.g., condensed tannins) competes directly with the synthesis of proteins, and therefore with plant growth, because of a common precursor, phenylalanine. In contrast, the biosynthesis of terpenoids and of hydrolyzable tannins proceeds presumably without direct competition with protein synthesis. Therefore, accelerated plant growth induced by fertilization may cause a reduction in concentrations of phenylpropanoids but may affect less or not at all the levels of other classes of secondary compounds. A meta-analysis based on fertilization experiments with 35 woody plant species supported the predicted differences fertilizing significantly decreased concentrations of phenylpropanoids but not of terpenoids or hydrolyzable tannins.
187 citations
TL;DR: It is predicted that some herbivore/pathogen species have evolved metal tolerance, and it is suggested that resulting high metal levels in herbivores/pathogens may defend them against their own predators.
Abstract: Metal hyperaccumulating plants contain very high metal contents. Because of the general toxicity of metals, chemically-mediated biotic interactions involving hyperaccumulating plants may differ greatly from those of non-hyperaccumulators. Recent research has demonstrated a defensive function for hyperaccumulated metals against herbivores and pathogens. We predict that some herbivore/pathogen species have evolved metal tolerance, and suggest that resulting high metal levels in herbivores/pathogens may defend them against their own predators. Little is known regarding interference and commensal interactions involving hyperaccumulating plants. Decreased competition may occur through an interference interaction similar to allelopathy, in which enrichment of metal in the soil under a hyperaccumulator plant's canopy may inhibit another plant species, thus resulting in “elemental allelopathy”. Metal enrichment of soil under hyperaccumulators also may result in commensalism if another plant species (possibly another hyperaccumulator) derives a benefit from growing in the metal-enriched soil under the canopy of a hyperaccumulating overstory plant. It seems likely that high-metal plant litter will host a specialized microflora of decomposers and may affect nutrient cycling rates. Mutualist biotic interactions also may be affected by the elevated metal contents of hyperaccumulating species. Mycorrhizal fungi may form mutualisms with hyperaccumulators, but the phenomenon is poorly-explored. The few cases investigated to date have not detected mycorrhizae. Pollination and seed dispersal mechanisms may require biotic vectors that might be affected by plant metal content. Hyperaccumulating plants may have solved this dilemma in three ways. First, some may rely on abiotic vectors for pollen or seed dispersal. Second, biotic vectors used by these species may have varied diets and thus dilute metal intake to non-toxic levels. Finally, biotic vectors may have evolved tolerance of elevated dietary levels of metals, and perhaps have become specialists on hyperaccumulator species.
163 citations
TL;DR: The results support the hypothesis that such bark beetles are adapted to recognize and avoid non-host angiosperm trees by responding to a broad spectrum of volatiles that can act in various blends with equal effect.
Abstract: Coupled gas chromatographic-electroantennographic detection (GC-EAD) analysis of the Porapak Q-captured volatiles from the bark of trembling aspen, Populus tremuloides Michx., revealed four compounds that consistently elicited antennal responses by mountain pine beetles (MPBs), Dendroctonus ponderosae Hopkins. One of these, 1-hexanol, disrupted the capture of MPBs in multiple-funnel traps baited with the aggregation pheromones trans-verbenol and exo-brevicomin and the host kairomone myrcene, a blend of semiochemicals that mediates the secondary attraction response in which beetles mass attack and kill living pines. The other three EAD-active aspen bark volatiles, benzyl alcohol, benzaldehyde and nonanal, were inactive alone, but in binary and ternary combinations contributed to a disruptive effect in an additive and redundant manner when all four aspen bark volatiles were tested in all possible binary and ternary blends. The best ternary blend and the quarternary blend achieved ≥ 80% disruption. The quarternary blend enhanced the disruptive effect of the antiaggregation pheromone verbenone in traps, raising the disruptive effect to 98%, and also enhanced the inhibition of attack on attractant-baited lodgepole pines. This is the first demonstration of specific compounds from the bark of angiosperm trees that disrupt the secondary attraction response of sympatric coniferophagous bark beetles. The results support the hypothesis that such bark beetles are adapted to recognize and avoid non-host angiosperm trees by responding to a broad spectrum of volatiles that can act in various blends with equal effect.
77 citations
TL;DR: The systematic distribution of the defensive polypropionates suggests that their defensive use has evolved several times among gastropods, and may mean that synthetic capacity has evolved more than once.
Abstract: Recent advances in both the systematics and the natural products chemistry of the order Sacoglossa (=Ascoglossa) in the gastropod subclass Opisthobranchia suggest a revised and improved historical account of the evolution of the group. Although the algal genus Caulerpa makes a suitable model for the ancestral food of the order, other siphonaceous algae are consistent with both morphological and chemical data. At an early evolutionary stage terpenoids are sequestered from the food, and used defensively, often with modification. With an evolutionary switch to different kinds of algal food, there is often a shift to other, related defensive chemicals. A switch to new food source sometimes leads to the abandonment of chemical defense, but in other cases there is de-novo synthesis of defensive metabolites. The synthesis of polypropionates, which are used defensively, occurs in some other gastropods, but otherwise is known only in fungi. The systematic distribution of the defensive polypropionates suggests that their defensive use has evolved several times among gastropods. Failure to detect them may mean that synthetic capacity has evolved more than once, or it may mean that they exist at low levels, perhaps having a non-defensive function.
70 citations
TL;DR: A graphical approach to quantitative nutrition that focuses on the interplay between behavioural and physiological components of nutritional regulation and some ecological determinants and longer-term, life history consequences of such decisions is described and extended.
Abstract: We describe and extend a graphical approach to quantitative nutrition that focuses on the interplay between behavioural and physiological components of nutritional regulation. The site of integration is the nutrient transfer function, which is the function describing the time course of nutrient transfer between serially connected nutritional compartments (e.g., from the gut to the blood). The relationship between the shape of the nutrient transfer function and the temporal patterns of feeding determines the values of two key quantitative parameters of nutrition: the rate ('power') and the efficiency of nutrient acquisition. The approach can be extended to consider, in addition to the short-term behavioural and physiological decisions made by animals, some ecological determinants and longer-term, life history consequences of such decisions. Most importantly, this category of models can provide insights into the interplay among the various nutrients in an animal's diet. We illustrate this using hypothetical examples, and also present preliminary data for the power-efficiency relationships of protein and digestible carbohydrates in locusts. Finally, we consider existing evidence for the various means available to these and other insects for regulating such relationships.
60 citations
TL;DR: The negative effects of these secondary metabolites on potential foulers, in conjunction with data demonstrating larval avoidance of dictyol-covered surfaces, suggest that these compounds could function as chemical defenses against fouling, and could select for larvae that avoid hosts producing these metabolites.
Abstract: A recent investigation showed that the brown seaweed Dictyota menstrualis was unfouled relative to co-occurring seaweeds, and that larvae of fouling invertebrates avoided settling on D. menstrualis due to chemicals on its surface. The secondary metabolites dictyol E and pachydictyol A are among the compounds found on this alga's surface. In the present study, we tested the effects of specific diterpenes from Dictyota on the survivorship, growth, and development of invertebrate larvae and developing juveniles that could foul seaweeds. Exposure to dictyol E, dictyol B acetate, pachydictyol A, and dictyodial from Dictyota menstrualis and D. ciliolata caused significant larval mortality, abnormal development, and reduce growth rates for three species of co-occurring invertebrates when their larvae were forced into contact with these metabolites. Larvae were damaged at metabolite concentrations as low as 5% of maximum possible surface concentrations of these compounds for the populations of Dictyota we studied. The negative effects of these secondary metabolites on potential foulers, in conjunction with data demonstrating larval avoidance of dictyol-covered surfaces, suggest that these compounds could function as chemical defenses against fouling, and could select for larvae that avoid hosts producing these metabolites.
52 citations
TL;DR: This is one of the first instances of an insect using a mixture of primary and secondary substances for defense against predators, and pure standards of shield compounds were found to be deterrent when assayed.
Abstract: Both adults and larvae of the sumac flea beetle, Blepharida rhois (Forster), are dietary specialists that feed on smooth sumac, Rhus glabra, on Long Island, NY. Instead of discarding their feces, B. rhois larvae retain it on their backs to form fecal 'shields'. We observed that ants attacking shielded larvae retreated and groomed vigorously, indicating the possible presence of chemical deterrents. To examine whether shields were chemical rather physical barriers against predation, we employed a generalist ant predator as a bioassay. Shields of larvae reared on R. glabra thwarted ants while larvae that had their shields removed were readily taken. Moreover, larvae reared on a substitute diet of lettuce were defenseless. However, protection was restored after their lettuce-derived shields were replaced with shields obtained from larvae reared on R. glabra. We then extracted and fractionated shields in order to locate active deterrents. To determine whether larvae synthesized defensive compounds or obtained them from the host, leaves were also analyzed and compared to the chemicals found in shields. The shield defense was a mixture of three fatty acids, a suite of tannins, their metabolites and phytol. All shield compounds or their precursors were obtained entirely from the host plant. Pure standards of shield compounds were found to be deterrent when assayed. This is one of the first instances of an insect using a mixture of primary and secondary substances for defense against predators.
49 citations
TL;DR: The results suggest that C11 metabolites are unusual among the known seaweed chemical defenses in that they are especially effective against mesograzers, which often consume seaweed spores, zygotes, and juveniles.
Abstract: A diverse group of brown seaweeds produce bouquets of C11 metabolites, some of which act as pheromones that cue gamete release or attract sperm to eggs following release. We demonstrate that these C11 metabolites and their degradation products also frequently and strongly deter feeding by the herbivorous amphipod Ampithoe longimana, but rarely by the herbivorous sea urchin Arbacia punctulata. Across the range of concentrations tested, seven of twelve C11 metabolites or mixtures that we tested deterred feeding by the amphipod, but only two of eleven deterred the sea urchin. For those compounds where we could rigorously contrast the magnitude of deterrence against the amphipod with the magnitude of deterrence against the urchin, the amphipod was deterred significantly more than the urchin by five of six metabolites. Thus, C11 compounds were more frequently and more strongly deterrent to the amphipod than to the sea urchin. These findings for C11 metabolites conflict with previous investigations, where other classes of seaweed chemical defenses have been shown to deter feeding by large mobile herbivores like urchins and fishes but to be relatively ineffective against mesograzers, especially the species of amphipod that we used here. Our results suggest that C11 metabolites are unusual among the known seaweed chemical defenses in that they are especially effective against mesograzers, which often consume seaweed spores, zygotes, and juveniles. The high concentrations of C11 metabolites in brown algal eggs could allow these defenses to be especially important in defending gametes, zygotes, or young sporelings from herbivorous mesograzers.
46 citations
TL;DR: The three active phytoalexins can explain only part of the activity of host-pant extracts but might induce a preference for infected plants.
Abstract: Bacteria species known to induce the biosynthesis of crucifer-specific phytoalexins have earlier been shown to be associated with Delia flies. Eleven crucifer-specific phytoalexins and related synthetic compounds were applied on surrogate paper leaves and offered to cabbage root flies in oviposition assays. Since three of these compounds (methoxybrassinin, cyclobrassinin, brassitin) proved to be significantly stimulatory whereas the remaining metabolites had no effect, the reaction of the fly appears to be structure-specific. Inactive phytoalexins had no inhibitory effect on oviposition. 100 μg of methoxybrassinin per surrogate leaf was as stimulatory as 0.05 gle (gram leaf equivalent) of a methanolic host-leaf (Brassica oleracea) extract. Thus the three active phytoalexins can explain only part of the activity of host-pant extracts but might induce a preference for infected plants.
41 citations
TL;DR: The results of this study suggest that non-linear mathematical analysis is a good tool for classification of castes based on cuticular hydrocarbon mixture and confirms that hydrocarbon mixtures observed are real chemical entities and constitute a true chemical signature or odor.
Abstract: Individuals in an insect colony need to identify one another according to caste. Nothing is known about the sensory process allowing nestmates to discriminate minute variations in the cuticular hydrocarbon mixture. The purpose of this study was to attempt to model caste odors discrimination in four species of Reticulitermes termites for the first time by a non-linear mathematical approach using an "artificial neural network" (ANN). Several rounds of testing were carried out using 1 – the whole hydrocarbon mixtures 2 – mixtures containing the hydrocarbons selected by principal component analysis (PCA) as the most implicated in caste discrimination. Discrimination between worker and soldier castes was tested in all four species. For two species we tested discrimination of four castes (workers, soldiers, nymphs, neotenics). To test cuticular pattern similarity in two sibling species (R. santonensis and R. flavipes), we performed two experiments using one species for training and the other for query. Using whole hydrocarbons mixtures, worker/soldier discrimination was always successful in all species. Network performance decreased with the number of hydrocarbons used as inputs. Four-caste discrimination was less successful. In the experiment with the sibling species, the ANN was able to distinguish soldiers but not workers. The results of this study suggest that non-linear mathematical analysis is a good tool for classification of castes based on cuticular hydrocarbon mixture. In addition this study confirms that hydrocarbon mixtures observed are real chemical entities and constitute a true chemical signature or odor. Whole mixtures are not always necessary for discrimination.
40 citations
TL;DR: In the marine polychaete Nereis succinea a sex pheromone was isolated from the coelomic fluid of sexually mature females and identified by NMR studies and independent synthesis as L-cysteine-glutathione disulfide.
Abstract: In the marine polychaete Nereis succinea (Frey & Leuckart 1847) a sex pheromone was isolated from the coelomic fluid of sexually mature females and identified by NMR studies and independent synthesis. This pheromone is released by the females during reproduction together with eggs and coelomic fluid into the free water column and induces sperm release of surrounding males. Its structure was ascertained as L-cysteine-glutathione disulfide. It exhibited a response threshold of 0.6 · 10−7 M.
TL;DR: The volume of secretion produced in the three Chrysochus species seems to be inversely correlated with the known toxicity of the compounds present in the secretion.
Abstract: Leaf beetles of the genus Chrysochus were shown to release secretions from pronotal and elytral glands when disturbed. This defensive reaction is similar to that observed in members of other, not closely related, subfamilies of the Chrysomelidae. In Chrysochus auratus and C. cobaltinus which both feed on plants of the genera Asclepias and Apocynum (Ascle piadaceae and Apocynaceae), the secretions contain cardenolides in a concentration of 77 to 358 μg/μl. Extracts of whole beetles contained cardenolides in concentrations too low for spectrophotometric quantification to a maximum of 748 μg/g dry weight. The cardenolides are apparently taken up from the food plant, since both plant genera contain these toxins and cardenolide pattern and concentration of whole beetle extracts and of the beetles' secretion depended on the local host plant. In C. asclepiadeus, which feeds on Vincetoxicum hirundinaria (Asclepiadaceae) devoid of cardenolides, phenylalanine, tryptophane, leucine and diacetyl putrescine were identified as major constituents of the secretions. The volume of secretion produced in the three Chrysochus species seems to be inversely correlated with the known toxicity of the compounds present in the secretion.
TL;DR: An aphidiid wasp, Paralipsis eikoae, was associated with both Lasius niger and L. sakagamii and both ant species rejected adult workers of the other species but accepted their larvae and pupae, it is suggested that the emerged wasp mimics ant cuticular hydrocarbons to integrate into the ant nest, acquiring the Hydrocarbons by mounting and rubbing against the ants.
Abstract: An aphidiid wasp, Paralipsis eikoae, was associated with both Lasius niger and L. sakagamii attending the wormwood root aphid Sappaphis piri. An L. sakagamii worker was observed carrying a winged female P. eikoae to its nest with its mandible, but it did not kill the wasp. Once accepted by the ants, the wasp often mounted and rubbed against the worker ants and sometimes teased them to regurgitate food to itself. No workers in the colony attacked the wasp. Conspecific foreign workers, however, viciously attacked the wasp when encountered. Gas chromatography-mass spectrometry analyses showed that the accepted wasp had complex cuticular hydrocarbons that were very similar to those of its host ants, whereas the winged wasps collected outside the ant nest showed only a series of n-alkanes. Additionally, the accepted wasp had a hydrocarbon profile closer to that of its host ants than to the conspecific foreign ants. We believe the wasp mimics ant cuticular hydrocarbons to integrate into the ant nest, acquiring the hydrocarbons by mounting and rubbing against the ants. In contrast, the cuticular hydrocarbons of the emerged wasp contained larval and pupal hydrocarbons of L. sakagamii that were also similar to those of L. niger. Both ant species rejected adult workers of the other species but accepted their larvae and pupae. We suggest that the emerged P. eikoae mimics the cuticular hydrocarbons of these Lasius larvae and pupae, which allows P. eikoae to be accepted by both L. sakagamii and L. niger.
TL;DR: The results show that olfactory occlusion results in low steroid hormone levels and milt volumes in precocious males placed in a spawning situation in brown trout males kept in a stream tank with a nest digging female.
Abstract: In the present experiment the behaviour and endocrine status of males of the brown trout, Salmo trutta L., (Salmoniformes: Salmonidae) were studied when males were kept in a stream tank with a nest digging female. Groups of mature adult males and precocious intact or anosmic male parr were placed with the nesting female so that the group resembled a natural spawning situation with big anadromous fish acting as dominant males and precocious parr acting as “sneakers”. A control experiment was also run with only males without a female present. In intact parr there were significant positive correlations between the per cent of the total observation time spent with a female, milt volume, and plasma concentration of 17α, 20β-dihydroxy-4-pregnen-3-one. Anosmic parr had significantly lower volumes of strippable milt and gonadal steroid hormone levels compared with intact parr. However, no differences were found in the control experiment. Significantly fewer anosmic parr attended and courted the nesting female and those anosmic fish that attended the female had significantly lower plasma levels of gonadal hormones. Intact parr also displayed a greater number of agonistic acts against other parr without any difference in fighting ability. No differences in aggression occured in the control experiment. In adult males together with a female, post-experimental gonadal steroid hormone levels were higher than pre-experimental levels. Positive correlations between aggression and androgen hormone levels were observed in adult males. No differences in plasma hormone levels were observed between adult males and intact precocious males. The results show that olfactory occlusion results in low steroid hormone levels and milt volumes in precocious males placed in a spawning situation. The courting behaviour was also affected by anosmia. Odours from the nesting female may have caused the enhanced plasma hormone levels and stimulated the males to attend the female.
TL;DR: 3-CmQA is found to be the major caffeoylcyclohexane-1-carboxylic acid isomer in plants of the genus Asimina, suggesting that responses by swallowtails to hydroxycinnamic acid derivatives as oviposition cues date back at least to the ancestor of the subfamily Papilioninae.
Abstract: We have isolated a caffeoylcyclohexane-1-carboxylic acid derivative, 3-caffeoyl-muco-quinic acid (3-CmQA), as a contact oviposition stimulant for the zebra swallowtail butterfly, Eruytides marcellus (Papilionidae), from the foliage of its primary host plant, Asimina triloba (Annonaceae). This compound alone was as active in stimulating oviposition by females as were the parent ethanolic plant extract and the host plant itself. Other tested isomers of 3-CmQA, including 5-caffeoylquinic acid (5-CQA or trans-chlorogenic acid), were inactive. We found, however, that experienced female butterflies responded strongly to host volatiles, which enhanced landing rates and hence oviposition.¶ This is the first report of an oviposition stimulant for a swallowtail butterfly of the tribe Graphiini. We found 3-CmQA to be the major caffeoylcyclohexane-1-carboxylic acid isomer in plants of the genus Asimina. These plants lack appreciable amounts of 5-CQA, which has been shown previously to be one of the oviposition stimulants for certain Rutaceae- or Apiaceae-feeding swallowtails of the related tribe Papilionini.¶ Our findings, along with earlier results from the tribes Troidini and Papilionini, suggest that responses by swallowtails to hydroxycinnamic acid derivatives as oviposition cues date back at least to the ancestor of the subfamily Papilioninae.
TL;DR: It is shown that the chemical composition of the Dufour gland is colony-specific and that workers can discriminate between secretions from their own and other colonies, and suggest that Dufouring gland secretions are involved in the establishment of hierarchies within a colony.
Abstract: Queens in colonies of the small myrmicine ant, Leptothorax gredleri Mayr 1855 (Hymenoptera, Formicidae) engage in dominance interactions and form social hierarchies, in which typically only the top-ranking queen lays eggs. Occasionally, queen antagonism escalates to violent mandible fighting, during which the sting is used to apply Dufour gland secretions onto the cuticle of the opponent. Contaminated queens often are attacked by nestmate workers. Here we show that the chemical composition of the Dufour gland is colony-specific and that workers can discriminate between secretions from their own and other colonies. Our findings suggest that Dufour gland secretions are involved in the establishment of hierarchies within a colony. When invading an alien colony the queen presumably employs the secretions during the expulsion of the resident queen. Apparently, Dufour gland secretions play a role in intraspecific queen competition similar to that in slave-making and inquiline formicoxenine ants, where they function as "propaganda substances" in an interspecific context.
TL;DR: Characteristics of Hx induction by aphid infestation in T. uniaristatum partially support the expected cost-saving patterns in the allocation of induced defenses.
Abstract: We characterized the induction of hydroxamic acids (Hx) by aphid infestation in the wild wheat Triticum uniaristatum by addressing the following questions: i) Do different leaves have similar responses to aphid damage?, ii) Is the Hx induction localized or systemic?, iii) How long does the induction last?, and iv) Is the degree of damage related to the magnitude of induced Hx? Based on earlier results on this wheat/aphid system (lack of costs of Hx induction) we expected to find the plant exhibiting cost-saving patterns of response to herbivory. Aphid infestation in the primary leaf led to induced levels of Hx, but no differences in Hx levels were found after infestation of the secondary leaf. Induction of Hx was restricted to the infested leaf (primary leaf). Induced Hx levels exhibited by the primary leaf at the end of aphid infestation were not observed 2 days later. Finally, different aphid densities (between 10 and 40 aphids per leaf) did not produce significant differences in Hx levels in infested primary leaves. Characteristics of Hx induction by aphid infestation in T. uniaristatum partially support the expected cost-saving patterns in the allocation of induced defenses.
TL;DR: In this article, the authors described isolation and identification of components of the egg release pheromone bouquet from the coelomic fluid of sexually mature males, including Inosine, L-glutamic acid, and Lglutamine.
Abstract: Pheromones released by male marine polychaetes Nereis succinea (Frey & Leuckart 1847) initiate egg release in mature females. Here we describe isolation and identification of components of the egg release pheromone bouquet from the coelomic fluid of sexually mature males. Inosine, L-glutamic acid and L-glutamine are identified to be components. Inosine, an egg release component, has a response threshold that is reduced eightfold by simultaneous presentation 1 : 1 with L-glutamic acid or L-glutamine. A fourth substance in the bouquet is tentatively identified as guanosine. The natural relative concentrations of all members of the pheromone bouquet and their mutual influence must still be explored.
TL;DR: It is hypothesized that optimisation of the chemical defences allocated to the seed by the maternal parent confers a significant advantage to the Seedling, whose energy is mainly committed to growth.
Abstract: We determined the localization of phenolic compounds in dormant seeds of two American species of Sesbania (Fabaceae) by a combination of histochemical and biochemical methods. Phenolics are located in different layers of the seed coat and in the subhilar parenchyma. We then investigated the release of these compounds by imbibing seeds of both species. The annual S. vesicaria releases the flavonoid luteolin, with minor amounts of proanthocyanidins, whereas the perennial S. drummondii releases mostly proanthocyanidins. Types and amount of allelochemicals exuded seem related to ecology and life history traits of each species. We then showed mobilisation of these allelochemicals by histochemical sections in imbibing seeds of both species. Histological structure is similar in both species. A number of characters (lens, subhilar parenchyma, tracheid bar) appear to function together to facilitate the exudation of compounds that protect young seedlings. Furthermore, the spatial organization of these organs with interlocking function allows retrieval of defensive substances stored in the seed, and their redeployment is beneficial for seedling survival. We hypothesize that optimisation of the chemical defences allocated to the seed by the maternal parent confers a significant advantage to the seedling, whose energy is mainly committed to growth.
TL;DR: It is found that induction of secondary metabolites in response to damage is largely restricted to a single class of compounds, the furanocoumarins, known to be toxic to a wide variety of insect herbivores.
Abstract: Induction of secondary metabolites to herbivore damage is a widespread phenomenon among plants and serves to enhance resistance by reducing suitability or increasing toxicity of foliage. Post-damage responses of primary metabolites are less well known; reductions in primary metabolites may increase resistance by decreasing palatability or nutritional suitability for herbivores or by potentiating toxicity of secondary metabolites. In this study, we examined response to simulated herbivory in Pastinaca sativa, the wild parsnip, in both primary and secondary metabolites. We found that induction of secondary metabolites in response to damage is largely restricted to a single class of compounds, the furanocoumarins. These prooxidant compounds are known to be toxic to a wide variety of insect herbivores. The only primary metabolite that responded to damage was total soluble protein, which increased significantly 24 h after damage. After 24 h, the correlation between total furanocoumarins and total sugars was significant and negative (r = − 0.697). This correlation likely reflects an independent response of sugar to damage, rather than a diversion of resources into furanocoumarin production, inasmuch as this correlation at 3 h, after furanocoumarin induction had taken place, was not significant. In other secondary metabolite pathways, damage produced a significant decline in farnesene and a C-16 unsaturated fatty acid, 7,10,13-hexadecatrienoic acid, each of which may potentiate the furanocoumarin defense response. Farnesene may enhance photooxidative activation of the furanocoumarins and 7,10,13-hexadecatrienoic acid may serve as a precursor to jasmonic acid, a key hormone in regulating induction responses. With few key exceptions, quantities of both primary and secondary metabolites in wild parsnip foliage are unaffected by damage. Those that are affected may well play a role in resistance of parsnips to herbivores.
TL;DR: Concentrations of furanocoumarins in seedlings are far lower than in adult plants, perhaps because the selective regime of seedlings differs from that of mature plants, and inter-seedling competition favors investment in growth rather than defense.
Abstract: To ascertain patterns of allocation between growth and defense in seedlings, we measured plant biomass and the amount of six furanocoumarin defensive chemicals in wild parsnip roots and shoots (Apiaceae: Pastinaca sativa L.) in sequential harvests for sixty days following emergence and compared them to previous studies on mature plants. Furanocoumarins were present from the first day of emergence and were actively synthesized from the onset of seedling growth. Although initial amounts of each furanocoumarin species differed, they were produced at the same rate. Furanocoumarin production was not commensurate with biomass accretion, and fluctuations in concentration varied dramatically between roots and shoots. Concentrations of furanocoumarins in seedlings are far lower than in adult plants, perhaps because the selective regime of seedlings differs from that of mature plants, and inter-seedling competition favors investment in growth rather than defense.
TL;DR: It is concluded that antixenotic resistance of host plants to carrot fly attack depends on complex mixtures of semiochemicals, including methanolic fraction, which apparently contains unknown stimulatory compounds.
Abstract: Foliage of twelve host and two non-host species and surrogate leaves treated with the respective leaf extracts were presented to laboratory populations of the carrot fly (Psila rosae) in oviposition choice assays. The stimulatory activity of dichloromethane surface extracts and the diethyl ether fraction of hot water extracts did not reflect accurately the differences in acceptability observed among intact leaves. A better correlation was found using hexane extracts prepared in a microwave oven. Two out of five fractions of this crude hexane extract obtained by silica gel column chromatography stimulated oviposition. The diethyl ether fraction, which contained the previously identified oviposition stimulants (propenylbenzenes, furanocoumarins, polyacetylenes), could account for only a minor part of the variation in the acceptability of host leaves. The preference hierarchy for intact leaves corresponded better to the ranking of species according to activity of the methanolic fraction, which apparently contains unknown stimulatory compounds.¶ The water fractions of the hot water extracts were shown to reduce egg-laying underneath surrogate leaves treated with a stimulatory extract. This oviposition-deterring effect was particularly strong with the non-preferred species Pimpinella major, which is also highly resistant in the field. Hence, unidentified inhibitory compounds may also contribute to differential accept ability of host plants. It is concluded that antixenotic (non-preference) resistance of host plants to carrot fly attack depends on complex mixtures of semiochemicals.
TL;DR: The results suggest that inter-individual variation in defensive chemistry in insects offered the same diet may be ecologically important.
Abstract: We tested whether inter-individual variation in concentration of sequestered compounds predicts defensive efficacy of the defensive secretion of onion-fed Eastern lubber grasshoppers. When fed onion, lubbers have the ability to sequester sulfur compounds into their defensive secretion, and the secretion from onion-fed lubbers is more deterrent of ants than the secretion from lubbers fed other diets (Jones et al. 1989). To test three hypotheses, we developed a method for measuring total sequestered sulfur in the secretion using energy dispersive spectroscopy (EDS). First, we found that lubbers fed an ad libitum, monophagous diet of onion produce more secretion and have higher concentrations of total sulfur in their secretions than lubbers fed other diets. These sulfur concentrations varied three-fold; we believe that this variation in the composition of defensive secretions stems from physiological variation. Second, our method was sensitive enough to detect sulfur in the secretion of some lubbers that had been fed onion only once. Third, the sulfur concentration of a secretion sample significantly predicted its ability to deter ants from foraging. Hence, our results suggest that inter-individual variation in defensive chemistry in insects offered the same diet may be ecologically important.
TL;DR: Workers of the amblyoponine species Mystrium rogeri employ trail communication during recruitment to food sources and new nest sites using a hitherto unknown sternal gland located in the 7th abdominal sternite, which elicits a repelling response in other ant species.
Abstract: Workers of the amblyoponine species Mystrium rogeri employ trail communication during recruitment to food sources and new nest sites. The trail pheromone originates from a hitherto unknown sternal gland located in the 7th abdominal sternite. The recruiting ant deposits the gland secretions by a special gaster-dragging behavior. The recruitment behavior can be complemented by a rapid vertical body shaking performed by some recruiting ants inside the nest. M. rogeri workers possess a large pygidial gland, the secretion of which elicits a repellent response in other ant species.
TL;DR: Significant differences were found in the relative EAG responses of apple and hawthorn flies to host fruit compounds at five of six paired study sites across the eastern United States, raising the possibility that antennal responses to fruit-related volatile compounds contribute to host plant discrimination in R. pomonella.
Abstract: Domestic apple (Malus pumila)- and hawthorn (Crataegus sp.)-infesting races of Rhagoletis pomonella, Walsh (Diptera: Tephritidae) provide an excellent model to examine the role that host plant specificity plays during sympatric speciation (i.e., divergence in the absence of geographic isolation). Previous work has shown that these races differ in their propensities to accept apple and hawthorn fruits in behavioral choice assays, and that this discrimination translates into "host fidelity" in the field (i.e., apple flies tend to mate on and oviposit into apples and hawthorn flies on hawthorns). ¶We present the results of a study examining possible physiological factors contributing to host choice differences in R. pomonella. We tested whether apple and hawthorn flies differ in their electroantennogram (EAG) responses to biologically relevant volatile compounds emitted from apples and hawthorns. Significant differences were found in the relative EAG responses of apple and hawthorn flies to host fruit compounds at five of six paired study sites across the eastern United States. The geographic pattern of EAG variation was complex, however, with local populations of apple and hawthorn flies tending to be more similar to one another than to flies of the same race at distant sites. This pattern was largely due to EAG responses for several compounds showing longitudinal or latitudinal clines, the latitudinal clines being similar to those observed for allozyme loci in the host races. We also found evidence for sex-related differences, as males tended to have higher mean EAG responses to compounds than females. Host-associated differences were therefore nested within geographic and sex-related differentiation in R. pomonella.¶Further behavioral studies are needed to distinguish whether the EAG differences are responsible for, as opposed to being a consequence of, host-plant fidelity and adaptation. Crosses are also required to establish a genetic basis for the EAG responses, although we did find significant correlations between EAG scores for several compounds and the allozymes NADH-Diaphorase-2 and Hydroxyacid dehydrogenase at one of the study sites. Questions therefore remain concerning the evolutionary significance of the EAG response differences between apple and hawthorn fly races. Nevertheless, these differences raise the possibility that antennal responses to fruit-related volatile compounds contribute to host plant discrimination in R. pomonella. Regardless, the EAG responses represent another set of traits, in addition to diapause/eclosion time phenotypes and allozyme frequencies, differing between apple and hawthorn host races of R. pomonella.