Biomedical subjects

Monika Hilker

Publications and source records attributed to Monika Hilker.

17 recordsLinked to original sources

PubMed2006

Defensive components in insect eggs: are anthraquinones produced during egg development?

Eggs of several insect species are protected against natural enemies by noxious components. However, almost nothing is known about the fate of these defensive substances during egg development nor their site of biosynthesis. The eggs of several leaf beetle species of the taxon Galerucini contain components that are unusual in insects: 1,8-dihydroxylated anthraquinones and anthrones that deter predators such as ants and birds. These components, i.e., the anthrones dithranol and chrysarobin, and the anthraquinones chrysazin and chrysophanol, are not sequestered from host plants. We asked whether the amounts of these components in the overwintering eggs of Galeruca tanaceti change from deposition to larval hatching. Gas chromatography-mass spectroscopy (GC-MS) analyses of eggs revealed a significant decrease in total amounts of dithranol and chrysophanol from egg deposition in autumn to the next spring 5 months later. Thus, these results do not provide any hint of active anthraquinone biosynthesis within eggs. Instead, the anthrones and anthraquinones that must be incorporated by the female into the eggs seem to be degraded to some extent either by the embryo or endosymbionts. GC-MS analyses showed that parasitization of eggs had some effects on the quantities of anthrones and anthraquinones.

Animals↗

PubMed2006

Different polyketide folding modes converge to an identical molecular architecture.

Metabolic diversity is being studied intensively by evolutionary biologists, but so far there has been no comparison of biosynthetic pathways leading to a particular secondary metabolite in both prokaryotes and eukaryotes. We have detected the bioactive anthraquinone chrysophanol, which serves as a chemical defense in diverse eukaryotic organisms, in a bacterial Nocardia strain, thereby permitting the first comparative biosynthetic study. Two basic modes of folding a polyketide chain to fused-ring aromatic structures have so far been described: mode F (referring to fungi) and mode S (from Streptomyces). We have demonstrated that in eukaryotes (fungi, higher plants and insects), chrysophanol is formed via folding mode F. In actinomycetes, by contrast, the cyclization follows mode S. Thus, chrysophanol is the first polyketide synthase product that is built up by more than one polyketide folding mode.

Animals↗

PubMed2006

Early herbivore alert: insect eggs induce plant defense.

Plants are able to "notice" insect egg deposition and to respond by activating direct and indirect defenses. An overview of these defenses and the underlying mechanisms is given from a tritrophic perspective. First, the interface between plant and eggs is addressed with respect to the mode of attachment of eggs on the plant surface. It is elucidated which plant cells might respond to components from insect eggs or the egg deposition. The scarce knowledge on the elicitors associated with the eggs or the egg-laying female is outlined. Since endosymbiotic microorganisms are often present on the eggs, and microorganisms are also abundant on the leaf surface, the role of these hidden players for eliciting oviposition-induced plant responses is considered. Furthermore, the question of which physiological and molecular processes are induced within the plant in response to egg deposition is addressed. Second, studies on the response of the herbivorous insect to oviposition-induced plant defenses are outlined. Third, the importance of oviposition-induced plant volatiles and contact cues for host and prey location of parasitoids and predators is discussed in the context of other informative chemicals used by carnivores when searching for food. Finally, physiological and ecological costs of oviposition-induced plant responses are addressed.

Animals↗

PubMed2006

Behavioral responses of Drosophila to biogenic levels of carbon dioxide depend on life-stage, sex and olfactory context.

Drosophila melanogaster (Meigen) detects and uses many volatiles for its survival. Carbon dioxide (CO(2)) is detected in adults by a special class of olfactory receptor neurons, expressing the gustatory receptor Gr21a. The behavioral responses to CO(2) were investigated in a four-field olfactometer bioassay that is new for Drosophila. We determined (1) whether the sensitivity of this response changes with odor context, and (2) if it depends on sex and life stage. When CO(2) was added to ambient air in one field and tested against ambient air in the three other fields, individually observed adults avoided CO(2) (0.1-1% above ambient), but did not respond to a low rise of 0.02%. We relate this behavior to measurements of CO(2) production in bananas and flies. When 0.02% CO(2) was combined with the odor of apple cider vinegar in one field of the olfactometer and tested against ambient air in the three other fields, the addition of CO(2) did not affect the attractiveness of apple cider vinegar alone. However, this combination of CO(2) and vinegar became repellent when it was tested against vinegar at ambient CO(2) concentrations in the three other fields. This ;odor background effect' was female-specific, revealing a sexually dimorphic behavior. The new assay allowed us to test larvae under similar conditions and compare their behavior to that of adults. Like adults, they avoided CO(2), but with lower sensitivity. Larvae lacking neurons expressing Gr21a lost their avoidance behavior to CO(2), but kept their positive response to vinegar odor. Hence, Gr21a-expressing neurons mediate similar behaviors in larvae and adults.

Acetic Acid↗

PubMed2005

A plant notices insect egg deposition and changes its rate of photosynthesis.

Scots pine (Pinus sylvestris) is known to change its terpenoid metabolism in response to egg deposition by the sawfly Diprion pini (Hymenoptera, Diprionidae). Three days after egg deposition, parts of the pine twig adjacent to the egg-laden one are induced to emit volatiles, which attract egg parasitoids. In this study, we investigated whether egg deposition by this sawfly affects pine photosynthesis. Measurements of photosynthesis were taken from untreated control twigs and from pine twigs adjacent to egg-laden ones (i.e. systemically oviposition-induced twigs) for a period of 3 d starting after egg deposition. The net photosynthetic rate of oviposition-induced pine twigs was lower than that of untreated control twigs, whereas the respiration rate of pine twigs was not affected by egg deposition. CO2 response curves of oviposition-induced twigs tended to be lower than those of controls. The potential rate of electron transport (J(max)) and the maximum rate of Rubisco activity (V(cmax)) were calculated from the data of the CO2 response curves. J(max) of oviposition-induced twigs was significantly lower than that of controls at day 1 after egg deposition, while the difference diminished from day 2 to day 3. A similar pattern was observed for V(cmax). Light response curves of oviposition-induced twigs were significantly lower than those of untreated ones during 3 d of measurements. Stomatal conductance was slightly lowered by egg deposition. When considering photosynthetic activity as a physiological currency to measure costs of induction of plant defense, the effects of insect egg deposition on gas exchange of pine are discussed with respect to known effects of insect feeding on the photosynthesis activity of plants.

Acclimatization↗

PubMed2005

The significance of background odour for an egg parasitoid to detect plants with host eggs.

Scots pine has been shown to produce a volatile bouquet that attracts egg parasitoids in response to oviposition of the herbivorous sawfly Diprion pini. Previous analyses of headspace volatiles of oviposition-induced pine twigs revealed only quantitative changes; in particular, the sesquiterpene (E)-beta-farnesene was emitted in significantly higher quantities by oviposition-induced pine. Here we investigated whether (E)-beta-farnesene attracted the egg parasitoid Chrysonotomyia ruforum. We tested the behavioural response of C. ruforum females to different concentrations of (E)-beta-farnesene. Egg parasitoids did not respond to this sesquiterpene at either concentration tested. However, they did respond significantly to (E)-beta-farnesene when this compound was offered in combination with the volatile blend emitted from pine twigs without eggs. This response was dependent on the applied concentration of (E)-beta-farnesene. Further bioassays with other components [(E)-beta-caryophyllene, delta-cadinene] of the odour blend of pine were conducted in combination with the volatile blend from egg-free pine as background odour. None of the compounds tested against the background of odour from an egg-free pine twig were attractive to the egg parasitoid. These results suggest that the egg parasitoids responded specifically to (E)-beta-farnesene, but only when this compound was experienced in the 'right' context, i.e. when contrasted with a background odour of non-oviposition-induced pine volatiles.

Animals↗

PubMed2005

Chemical communication: butterfly anti-aphrodisiac lures parasitic wasps.

To locate their hosts, parasitic wasps can 'eavesdrop' on the intraspecific chemical communications of their insect hosts. Here we describe an example in which the information exploited by the parasitic wasp Trichogramma brassicae is a butterfly anti-aphrodisiac that is passed from male to female Pieris brassicae butterflies during mating, to render them less attractive to conspecific males. When the tiny wasp detects the odour of a mated female butterfly, it rides on her (Fig. 1) to her egg-laying sites and then parasitizes the freshly laid eggs. If this fascinating strategy is widespread in nature, it could severely constrain the evolution of sexual communication between hosts.

Acetonitriles↗

PubMed2005

Ipangulines and minalobines, chemotaxonomic markers of the infrageneric Ipomoea taxon subgenus Quamoclit, section Mina.

A comprehensive GC-MS analysis of 8 Ipomoea species belonging to the subgenus Quamoclit, section Mina revealed that the members of this taxon form combinations of two necine bases with rare necic acids resulting in unique pyrrolizidine alkaloids. The occurrence and diversity of these metabolites show remarkable variations: Some species, especially Ipomoea hederifolia and Ipomoea lobata, are able to synthesize a large number of alkaloids whereas others, especially Ipomoea coccinea and Ipomoea quamoclit, are poor synthesizers with only a few compounds. However, these metabolites are apparently chemotaxonomic markers of this infrageneric taxon in general. They represent either esters of (-)-platynecine (altogether 48 ipangulines and 4 further esters including results of a previous study) or esters of (-)-trachelanthamidine, an additional novel structural type called minalobines (altogether 21 alkaloids). Both types are characterized by section-specific rare necic acids, e.g., ipangulinic/isoipangulinic acid, phenylacetic acid. The alkaloids of Ipomoea cholulensis, I. coccinea, I. hederifolia, Ipomoea neei, and Ipomoea quamoclit were mono and diesters of platynecine. Minalobines turned out to be metabolites of I. lobata (Cerv.) Thell. (syn.: Mina lobata Cerv.) lacking ipangulines. The major alkaloid of this species, minalobine R, has been isolated and identified as 9-O-(threo-2-hydroxy-2-methyl-3-phenylacetoxy-butyryl)-(-)-trachelanthamidine on the basis of spectral data. Apparently only two of the species included in this study, Ipomoea cristulata and Ipomoea sloteri, are able to synthesize both, ipangulines as well as minalobines. Minalobine O could be isolated as a major alkaloid of I. cristulata, its structure has been established as 9-O-(erythro-2-hydroxy-2-methyl-3-tigloyloxy-butyryl)-(-)-trachelanthamidine on the basis of spectral data.

Gas Chromatography-Mass Spectrometry↗

PubMed2005

Chemotaxonomy of the pantropical genus Merremia (Convolvulaceae) based on the distribution of tropane alkaloids.

The occurrence and distribution of tropane and biogenetically related pyrrolidine alkaloids in 18 Merremia species of paleo-, neo-, and pantropical occurrence have been studied. The extensive GC-MS study included members of almost all sections of the genus and has been carried out with epigeal vegetative parts as well as with roots. It comprises altogether 74 tropanes and 13 pyrrolidines including nicotine. Along with datumetine known already from a solanaceous species, the study led to the isolation (from M. dissecta and M. guerichii, respectively) and structure elucidation (spectral data) of four novel 3alpha-acyloxytropanes, merresectines A-D: 3alpha-(4-methoxybenzoyloxy)nortropane (A), 3alpha-kurameroyloxytropane (B), 3alpha-nervogenoyloxytropane (C), 3alpha-[4-(beta-D-glucopyranosyloxy)-3-methoxy-5-(3-methyl-2-butenyl)benzoyloxy]tropane (beta-d-glucoside of D). Moreover, the novel 3alpha,6beta-di-(4-methoxybenzoyloxy)tropane (merredissine) has been isolated from M. dissecta and structurally elucidated. In addition the structures of datumetine and merresectine A could be confirmed by synthesis. Spectral data for two known 3alpha-acyloxytropanes (merresectine E beta-D-glucoside, 4'-dihydroconsabatine) and one known 3beta-acyloxytropane (concneorine) are documented for the first time. The structures of three further merresectines (F-H) have been determined by mass spectrometry. Furthermore, the linkage (2',3- and 2',4-, respectively) of two position isomer N-methylpyrrolidinylhygrines was proven by synthesis. The results of the study contribute to the solution of infrageneric taxonomic problems. Whereas all species yield pyrrolidine alkaloids without suitably differentiating results the diverging occurrence of tropane alkaloids leads to three groups of sections: (1) taxa free of tropanes, (2) taxa with simple tropanes, and (3) taxa with merresectines in addition to simple tropanes.

Alkaloids↗

PubMed2005

Insect egg deposition induces defence responses in Pinus sylvestris: characterisation of the elicitor.

Egg deposition by the phytophagous sawfly Diprion pini L. (Hymenoptera, Diprionidae) is known to induce locally and systemically the emission of volatiles in Scots pine (Pinus sylvestris L.) that attract the egg parasitoid Chrysonotomyia ruforum Krausse (Hymenoptera, Eulophidae). The egg parasitoids kill the eggs and thus prevent damage to the plant from feeding sawfly larvae. The elicitor inducing the pine's response is known to be located in the oviduct secretion which the female sawfly applies to the eggs when inserting them into a slit in the pine needle using the sclerotized ovipositor valves. In this study we have characterized the elicitor. The elicitor was still active when isolated from the oviduct and applied directly to slits made in the pine needles. However, as soon as the oviduct secretion was dissolved in Aqua dest. and stored for 3 h at room temperature or kept frozen at -80 degrees C, its activity was lost. In contrast, oviduct secretion kept its eliciting activity, when dissolved in Ringer solution (pH 7.2) both after storage at room temperature and after freezing. The activity of the elicitor vanished after treatment of the oviduct secretion with proteinase K, which destroyed all proteins. This suggests that the elicitor in the oviduct secretion is a peptide or protein, or a component bound to these. SDS-PAGE revealed a similar, but not identical protein pattern from hemolymph and oviduct secretion. Hemolymph itself has no eliciting effect. The elicitor in the oviduct secretion is only active when transferred to slit pine needles, since its application on undamaged needles did not induce the emission of attractive volatiles.

Analysis of Variance↗

PubMed2004

Analysis of volatiles from black pine (Pinus nigra): significance of wounding and egg deposition by a herbivorous sawfly.

The composition of headspace volatiles of black pine (Pinus nigra) was analysed by coupled gas chromatography-mass spectrometry (GC-MS). It has been shown in a previous study that egg deposition of the sawfly Diprion pini on P. sylvestris induces a quantitative change of the pine volatile blend . Chrysonotomyia ruforum, an egg parasitoid of D. pini, is known to be attracted by volatiles from egg-carrying P. sylvestris, but not by odour from egg-laden P. nigra. Therefore, the present study focused on the question whether also P. nigra as another host plant of this sawfly responds to egg deposition by change of its volatile blend. The headspace of untreated, egg-carrying, and artificially wounded P. nigra twigs were compared. The artificial damage inflicted to the twigs mimicked the damage by the sawfly female prior to egg deposition. Thirty five mainly terpenoid compounds that were identified in more than 50% of the egg-carrying P. nigra twigs could also be detected in the headspace of untreated and artificially wounded twigs. Quantitative differences of the blends of volatiles from differently treated P. nigra twigs were compared by multivariate data analyses. PLS-DA (projection to latent structures-discriminant analysis) revealed that blends of volatiles from differently treated P. nigra differed significantly. When comparing volatiles from egg-carrying and artificially wounded P. nigra with respective P. sylvestris samples, qualitative and quantitative differences were detected. The differences in volatile composition of P. nigra and P. sylvestris are discussed with special respect to the egg parasitoid's response to odours of egg-carrying pine twigs.

Animals↗

PubMed2003

Indirect interactions between a phytopathogenic and an entomopathogenic fungus.

Slow growth in herbivores may lead to higher mortality, due to prolonged exposure to natural enemies. A number of studies has tested the 'slow-growth, high-mortality' hypothesis using predators or parasitoids as natural enemies of the herbivore, but the possible role of pathogens is poorly documented. We provide evidence that phytopathogenic infection of a plant enhances the susceptibility of herbivore larvae to a generalist entomopathogen. Larvae of the mustard leaf beetle Phaedon cochleariae grow more slowly when feeding on Chinese cabbage leaves infected by the phytopathogenic fungus Alternaria brassicae than larvae feeding on healthy leaves. Treatment of such larvae feeding on diseased plants with an LD(50) of the entomopathogenic fungus Metarhizium anisopliae resulted in 100% mortality, compared with a mortality rate of 54% in the control larvae feeding on uninfected leaves. This is the first demonstration of an interaction between a phyto- and an entomopathogenic fungus.

Alternaria↗

PubMed2003

Chemical analysis of volatiles emitted by Pinus svlvestris after induction by insect oviposition.

Gas chromatography-mass spectrometry analyses of the headspace volatiles of Scots pine (Pinus sylvestris) induced by egg deposition of the sawfly Diprion pini were conducted. The odor blend of systemically oviposition-induced pine twigs. attractive for the eulophid egg parasitoid Chrysonotomyia ruforum, was compared to volatiles released by damaged pine twigs (control) that are not attractive for the parasitoid. The mechanical damage inflicted to the control twigs mimicked the damage by a sawfly female prior to egg deposition. The odor blend released by oviposition-induced pine twigs consisted of numerous mono- and sesquiterpenes, which all were also present in the headspace of the artificially damaged control twigs. A quantitative comparison of the volatiles from oviposition-induced twigs and controls revealed that only the amounts of (E)-beta-farnesene were significantly higher in the volatile blend of the oviposition-induced twigs. Volatiles from pine twigs treated with jasmonic acid (JA) also attract the egg parasitoid. No qualitative differences were detected when comparing the composition of the headspace of JA-treated pine twigs with the volatile blend of untreated control twigs. JA-treated pine twigs released significantly higher amounts of (E )-beta-farnesene. However, the JA treatment induced a significant increase of the amount of further terpenoid components. The release of terpenoids by pine after wounding, egg deposition, and JA treatment is discussed with special respect to (E)-beta-farnesene.

Adaptation, Physiological↗

PubMed2002

Alcoholism in cockchafers: orientation of male Melolontha melolontha towards green leaf alcohols.

Chemical orientation of the European cockchafer, Melolontha melolontha L., a serious pest in agriculture and horticulture, was investigated by field tests and electrophysiological experiments using plant volatiles. In total, 16 typical plant volatiles were shown to elicit electrophysiological responses in male cockchafers. Funnel trap field bioassays revealed that green leaf alcohols (i.e. (Z)-3-hexen-1-ol, (E)-2-hexen-1-ol and 1-hexanol) attracted males, whereas the corresponding aldehydes and acetates were behaviourally inactive. Furthermore, male cockchafers were attracted by volatiles from mechanically damaged leaves of Fagus sylvatica L., Quercus robur L. and Carpinus betulus L. However, volatiles emitted by damaged leaves of F. sylvatica attracted significantly more males than those from the other host plants. Odour from intact F. sylvatica leaves was not attractive to M. melolontha males. Females were not attracted by any of the tested volatile sources. The results suggest that plant volatiles play a similar role as a sexual kairomone in mate finding of M. melolontha, as has been shown for the forest cockchafer, Melolontha hippocastani F. Nevertheless, both species show remarkable differences in their reaction to green leaf alcohols.

Alcohols↗

PubMed2002

Antimicrobial activity of exocrine glandular secretion of Chrysomela larvae.

The exocrine glandular secretions of leaf beetle larvae of the taxon Chrysomela are well-known defensive devices used against some generalist predators. Salicylaldehyde is the major repellent component of secretions emitted by larvae of Chrysomela vigintipunctata and C. lapponica, which feed on salicin-rich Salicaceae. In this study, we examined whether salicylaldehyde is also active against the entomopathogenic fungus Metarhizium anisopliae. The germination and growth of this fungus was strongly inhibited when salicylaldehyde was applied directly onto the blastospores. The salicylaldehyde concentration of the larval secretions of the tested willow feeding Chrsysomela larvae was much higher than the one necessary to display this antifungal activity. Additionally, salicylaldehyde was shown to reduce germination and growth of M. anisopliae via the gas phase over a distance of 45 mm. Further studies on the antimicrobial activity of the salicylaldehyde-containing secretions of Chrysomela larvae revealed that they act nonspecifically against prokaryotic (Escherichia coli) and eukaryotic cells (Saccharomyces cerevisiae and Trichoplusia ni). All antimicrobial and cytotoxic effects detected proved to be due to salicylaldehyde. The larval secretions of the birch-feeding allospecies of C. lapponica, that do not contain salicylaldehyde, but mainly carboxylic acids and their esters, showed no detectable effects on bacteria or fungi and no cytotoxic effects against insect cells. The results are discussed with respect to their ecological relevance.

Aldehydes↗

PubMed2002

Insect egg deposition induces Pinus sylvestris to attract egg parasitoids.

Plant volatiles released in response to feeding insects are known to attract enemies of the feeding herbivores. In this study, egg deposition by a herbivorous insect was shown to induce a gymnosperm plant to emit volatiles that attract egg parasitoids. Odour from twigs of Pinus sylvestris laden with egg masses of the pine sawfly Diprion pini attracts the eulophid egg parasitoid Chrysonotomyia ruforum. Volatiles released from pine twigs without diprionid eggs are not attractive. Oviposition by the sawfly onto pine needles induces not only a local response in pine needles laden with eggs but also a systemic reaction. Needles without eggs but adjacent to those bearing diprionid eggs also release the volatiles that attract the egg parasitoid. The elicitor of the attractive volatiles was shown to be present in the oviduct secretion coating the eggs of D. pini. When pine twigs are treated with jasmonic acid, a well-known plant wound signal, they emit volatiles that attract the egg parasitoid. These results show, for the first time, that a gymnosperm plant is able to attract parasitoids as soon as a herbivore has deposited its eggs on it. Thus, the plant appears to defend itself against herbivores prior to being damaged by feeding larvae.

Animals↗

PubMedDate not supplied

Phenol--another cockchafer attractant shared by Melolontha hippocastani Fabr. and M. melolontha L.

The response of the two most abundant cockchafer species in central Europe, Melolontha hippocastani and M. melolontha, towards phenol, mixtures of phenol with the leaf alcohol (Z)-3-hexen-1-ol and the known cockchafer pheromones, 1,4-benzoquinone (M. hippocastani) and toluquinone (M. melolontha), was investigated in the field. During the swarming period at dusk, phenol attracted males of both species, and enhanced the known attraction of cockchafer males towards (Z)-3-hexen-1-ol. A mixture of phenol plus (Z)-3-hexen-1-ol was less attractive for M. hippocastani males than a mixture of (Z)-3-hexen-1-ol plus 1,4-benzoquinone, whereas phenol plus (Z)-3-hexen-1-ol attracted as many M. melolontha males as a mixture of (Z)-3-hexen-1-ol plus toluquinone. In both species three component mixtures containing phenol, (Z)-3-hexen-1-ol, and the respective benzoquinone did not capture more males than two component mixtures consisting of only (Z)-3-hexen-1-ol and the benzoquinone. A possible role of phenol as another cockchafer sex pheromone component is discussed.

Animals↗