Detoxification of the glucosinolate-myrosinase system by generalist lepidopteran herbivores

Das Glucosinolat-Myrosinase-System ist ein chemisches Abwehrsystem der Pflanzen der Ordnung Brassicales. Es besteht aus den ungiftigen Glucosinolaten und der Thioglucosidase Myrosinase, die getrennt voneinander gespeichert werden. Bei Gewebeverletzung kommt es zum Kontakt der beiden Komponenten und zur Freisetzung der eigentlich biologisch aktiven Abwehrstoffe, der giftigen Isothiocyanate und weiterer Hydrolyseprodukte. Unter den Lepidoptera haben sowohl Spezialisten als auch Generalisten Anpassungsmechanismen an diese pflanzliche Abwehr ausgebildet und können Brassicaceen als Wirtspflanzen nutzen. Die Mechanismen der Generalisten sind noch wenig untersucht und waren Thema dieser Arbeit. Für zwei Modellorganismen, Spodoptera exigua und S. littoralis, konnte die Ausscheidung von intaktem Benzylglucosinolat und weiterer Ausscheidungsprodukte mit dem Kot gezeigt werden. Eine Sequestrierung fand nicht statt. Als möglicher Mechanismus für die Ausscheidung von intaktem Benzylglucosinolat wurde in ersten Versuchen ein hemmender Effekt von Darmextrakten auf die Myrosinaseaktivität gefunden. Die identifizierten Hauptmetabolite waren N-Benzylmalonaminsäure als Metabolit des Benzylisothiocyanats und Hippursäure als Metabolit des Phenylacetonitrils. Als zusätzliche Ausscheidungsprodukte wurden N-Benzyl-dithiocarbamidsäure-S-D-glucosid und Benzylisothiocyanat-Glutathionkonjugat identifiziert. Beide traten sporadisch im Kot der Larven auf. Anhand dieser Ergebnisse kann die Anpassung der untersuchten Generalisten als Zusammenspiel von zwei Vorgängen beschrieben werden, der Hemmung der Myrosinaseaktivität und der Metabolisierung der Hydrolyseprodukte.Plants of the order Brassicales defend themselves against biotic stresses by the glucosinolate-myrosinase system. This activated plant defense is composed of the non toxic glucosinolates and the thioglucosidase myrosinase which are stored separately. Disruption of plant tissue brings the two components together leading to the formation of biologically active products such as toxic isothiocyanates. Specialist as well as generalist lepidopteran herbivores have evolved counteradaptations against this chemical defense enabling them to use these plants as host plants. The mechanisms of adaptation of generalists have been the subject of this work. When fed with benzylglucosinolate-containing plant material, the two investigated generalist model species, Spodoptera exigua and S. littoralis, excreted a proportion of benzylglucosinolate unchanged with the feces along with several metabolites. No sequestration was detected. As a potential mechanism allowing the excretion of intact glucosinolate an inhibitory effect on myrosinase activity was detected in gut extracts. Following metabolites have been identified in the larval feces: N-benzyl malonaminic acid as a metabolite of benzylisothiocyanate and hippuric acid as a metabolite of phenylacetonitrile. In addition, two metabolites, N-benzyl-dithiocarbamic acid-S-D-glucoside and benzylisothiocyanate-glutathione conjugate occurred sporadically. Based on these data, it is suggested that two principle mechanisms are responsible for the ability of the investigated generalists to feed on glucosinolate-containing plants: inhibition of myrosinase and metabolism of glucosinolate hydrolysis products for excretion with the feces

A Plagionotus arcuatus ssp. arcuatus darázscincér (Coleoptera: Cerambycidae) fajon belüli kommunikációjának a vizsgálata két, földrajzilag távoli, európai populáción

A bársonyos darázscincér, Plagionotus arcuatus ssp. arcuatus (L.) Európa nagyobb részén gyako- rinak számító szaproxilofág cincér faj, melyet a nyári hónapokban a szabadban tárolt, frissen kivágott tölgyfa alkalmi kártevőjeként tartunk számon. Annak érdekében, hogy azonosítsuk azokat a csalo- gató illatanyagokat, amelyek felhasználhatók a faj rajzáskövetésére, illatanyag gyűjtést végeztünk az imágókból, majd szabadföldi viselkedésvizsgálatokat végeztünk az azonosított illatanyagokkal, melyek a faj lehetséges aggregációs feromon komponensei. Három vegyület, az (R)-3-hidroxihexán- 2-on, az (R)-3-hidroxioktán-2-on, és az (R)-3-hidroxidekán-2-on viszonylag nagy mennyiségben volt jelen a hím kivonatokban Magyarországon és Svédországban egyaránt, függetlenül a filter típusától (aktív szén vagy PorapakTM Q, ezeket a bogarak által kibocsátott illatanyagok megkötésére hasz- náljuk), illetve függetlenül a kivonat készítésére használt oldószer típusától (hexán, dietil éter, vagy diklórmetán). A hidroxi-keton és annak rokon vegyületeinek egyike sem volt kimutatható a nőstények- ből származó kivonatokban. A szabadföldi vizsgálatokban mindkét országban a C6 és a C10 illatanya- gok keveréke, illetve a háromkomponensű keverék csalogatta a legtöbb bogarat. A kontroll csapdák, más kombinációk illetve az önmagukban alkalmazott illatanyagok csalogató hatása nem volt jelen- tős. A hímek és nőstények hasonlóan reagáltak a kezelésekre. Eredményeink azt mutatják, hogy a (R)-3-hidroxihexán-2-on és a (R)-3-hidroxidekán-2-on a bársonyos darázscincér hímek által termelt aggregációs feromon komponensei, míg a (R)-3-hidroxioktán-2-on szerepe nem tisztázott. Az azo- nosított feromonkomponensek a bársonyos darázscincér populáció megfigyelésére alkalmazhatóak

Revealing hidden species distribution with pheromones: the case of Synanthedon vespiformis (Lepidoptera: Sesiidae) in Sweden

Synanthedon vespiformis L. (Lepidoptera: Sesiidae) is considered a rare insect in Sweden, discovered in 1860, with only a few observations recorded until a sex pheromone attractant became available recently. This study details a national survey conducted using pheromones as a sampling method for this species. Through pheromone trapping we captured 439 specimens in Southern Sweden at 77 sites, almost tripling the number of previously reported records for this species. The results suggest that S. vespiformis is truly a rare species with a genuinely scattered distribution, but can be locally abundant. Habitat analyses were conducted in order to test the relationship between habitat quality and the number of individuals caught. In Sweden, S. vespiformis is thought to be associated with oak hosts, but our attempts to predict its occurrence by the abundance of oaks yielded no significant relationships. We therefore suggest that sampling bias and limited knowledge on distribution may have led to the assumption that this species is primarily reliant on oaks in the northern part of its range, whereas it may in fact be polyphagous, similar to S. vespiformis found as an agricultural pest in Central and Southern Europe. We conclude that pheromones can massively enhance sampling potential for this and other rare lepidopteran species. Large-scale pheromone-based surveys provide a snapshot of true presences and absences across a considerable part of a species national distribution range, and thus for the first time provide a viable means of systematically assessing changes in distribution over time with high spatiotemporal resolution

Tree recovery during the aftermath of an outbreak episode of the Hungarian spruce scale in southern Sweden

In 2010, the first, and so far only, infestation of the Hungarian spruce scale (Physokermes inopinatus) and accompanying sooty mould occurred in Scania, southernmost Sweden. About 1000 ha of Norway spruce (Picea abies) were affected, and the trees suffered from the sucking of the insects as well as from the dense sooty mould that covered the needles. Salvage cuttings were carried out in many of the massively attacked forest stands, both in response to the fear that the trees otherwise would die, e.g. from secondary bark beetle attacks and to prevent spreading of the infestation. The aim of this study was to provide basic, quantitative knowledge on the aftermath response of trees that were heavily infested, but not exposed to salvage cutting. Growth characteristics, in terms of needle weight, shoot length and tree-ring size were measured on infested and uninfested trees to compare and contrast the spruce growth before, during and after the scale outbreak. The infestation resulted in dwarf annual shoots, stunted needles and thin tree rings. The needle weight returned to normal the following year, whereas shoot length and tree rings required one growing season before full recovery

Common Cerambycid Pheromone Components as Attractants for Longhorn Beetles (Cerambycidae) Breeding in Ephemeral Oak Substrates in Northern Europe

Longhorn beetles are ecologically important insects in forest ecosystems as decomposers of woody substrates, microhabitat engineers, and as components of forest food webs. These species can be greatly affected both positively and negatively by modern forestry management practices, and should be monitored accordingly. Through headspace sampling, coupled gas chromatography-electroantennography, gas chromatography-mass spectrometry, and field bioassays, we identified two compounds, 2-methyl-1-butanol and 3-hydroxy-2-hexanone, that constitute aggregation-sex pheromone attractants of three cerambycid species which breed primarily in different types of fresh, recently dead oak wood in Northern Europe: Pyrrhidium sanguineum (L.), Phymatodes alni ssp. alni (L.), and Phymatodes testaceus (L.) (Cerambycinae: Callidiini). Analyses of headspace volatiles collected from live insects indicated that the male-produced aggregation-sex pheromone of P. sanguineum is a 1-15:100 blend of (R)-2-methyl-1-butanol and (R)-3-hydroxy-2-hexanone, whereas the corresponding ratios for P. alni were 70-110:100. In field bioassays, adult P. sanguineum and P. alni were significantly attracted to multiple blends with varying ratios of the two compounds. When tested individually, the compounds were minimally attractive. In contrast, adult P. testaceus exhibited nonspecific attraction to both of the individual compounds and to different blends, despite the hydroxyketone not being part of its pheromone, which consists of (R)-2-methyl-1-butanol alone. Overall, our results suggest that a blend of 50:100 of racemic 2-methyl-1-butanol and 3-hydroxy-2-hexanone is appropriate for parallel, cost-efficient pheromone-based monitoring of all three species. In particular, these species could serve as useful indicators of how modern forestry practices affect a whole guild of saproxylic insects that require ephemeral deadwood substrates for successful breeding

Characteristic scale of response for <i>Elater ferrugineus</i> using two models.

<p>i) Pooled density of trees within the groups <i>Quercus</i>, Noble 1 and Noble 2, and ii) density of <i>Quercus</i> only. The grey line indicates p<0.05, corresponding to Wald value 3.9.</p

Maps of predicted occurrence of <i>Elater ferrugineus.</i>

<p>The maps show >25%, >50%, >75% and >90% probability of occurrence in the study area (<b>a,b,c,d</b>) and in the county of Östergötland (<b>e,f</b>) and the trap capture. Empty traps are presented by crosses (×) while occupied traps are marked with open circles (Ο) which size is proportional to the number of individuals caught. The first column (<b>a,c,e</b>) shows predictions based on models including the pooled density of trees within the groups <i>Quercus</i>, Noble 1 and Noble 2, while the second column (<b>b,d,f</b>) shows predictions based on models including the density of <i>Quercus</i> only. (<b>a,b</b>) shows trap captures in systematically placed traps, (<b>c,d</b>) the strategically sampled validation data and (<b>e,f</b>) the validation data set sampled in the entire Östergötland. In each map, the predictions are based on two models, one for each characteristic scales of response (blue tones represent a smaller scale: 433 m (pooled density of <i>Quercus</i>, Noble 1 and Noble 2) and 327 m (density of <i>Quercus</i> only), while orange tones represent prediction at larger scale: 4051 m (<i>Quercus</i>, Noble 1 and Noble 2) and 4658 m (<i>Quercus</i>).</p

The relationships between occurrence of <i>Elater ferrugineus</i> and density of trees in different hollow classes.

<p>The relationships are expressed as Wald-values from 63 simple binomial GLMs. The explanatory variable ‘tree density’ is measured at 31 different spatial scales and includs trees from three different tree hollow classes: hollow trees ≥1 m dbh, hollow trees <1 m dbh and non-hollow trees. All models showed positive relationship between probability of occurrence and tree density. The grey line indicates p<0.05, corresponding to Wald value 3.9.</p