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Das Wirtswahlverhalten von Blattläusen wird neben primären Nahrungskomponenten auch durch sekundäre Pflanzeninhaltsstoffe gesteuert (Klingauf & al. 1978; Singh 1980; Powell & al. 1999; Campo & al. 2003). Häufig entziehen sich diese jedoch einer gezielten Untersuchung ihrer Wirkung auf die Aphiden, da sie als Substanzgemisch vorliegen. Beziehungen zwischen Substanzkonzentration und Verhaltensmustern aus Electrical Penetration Graphs (EPG) sind nur mit mäßigem Erfolg über statistische Verfahren darzustellen. Eine Versuchsanordnung zur gezielten Prüfung verhaltensbeeinflussender Substanzen mittels EPG wäre in diesem Falle hilfreich. Ein geeignetes einfaches Testsystem müsste mindestens folgende Komponenten beinhalten: – eine von den Aphiden akzeptierte Oberfläche, welche die Kutikula / Epidermis eines natürlichen Systems nachbildet – diese Oberfläche sollte evtl. durch den Versuchsansteller manipulierbar sein – eine dem Parenchym entsprechende Schicht, in welche die Testsubstanzen einzubringen wären – eine flüssige Phase, die dem Phloem entspricht und ebenfalls in ihrer Zusammensetzung variiert werden kann.
Cantharidin, which is mainly found in blister beetles (Coleoptera: Meloidae), is one of the most intensively studied natural products of insect (Dettner, 1997; McCormick & Carrel, 1987). The involvement of cantharidin in courtship behaviour has been already confirmed for certain canthariphilous insects (Eisner & al. 1996a,b; Frenzel & Dettner 1994; Frenzel & al. 1992; Schütz & Dettner, 1992; Hemp & al. 1999). The function and intrinsinc role of cantharidin in the courtship behaviour of Meloids has been never fully established. McCormick & Carrel (1987) only suggested that cantharidin might be used by female meloids when selecting a mate at close range. Pinto (1974, 1975) was, in fact, the first to consider male cuticular pores as being involved in the courtship behaviour of species from the genus Linsleya and Tegrodera (Meloidae). Based on morphology and chemical analyses of Cyaneolytta sp. (Coleoptera: Meloidae), we have hereby provided some further evidences that cantharidin may act as an infochemical in courtship behaviour of meloid beetles.
Sexual deception of male bees is one of the most remarkable mechanisms of pollination (Ackermann 1986, Proctor & al. 1996). Flowers of the orchid genus Ophrys mimic females of their pollinator species, usually bees and wasps, to attract males, which try to copulate with the flowers. During this so-called “pseudocopulation” the male removes the pollinia and transfers them to another flower to ensure pollination. Apart from visual and tactile cues, floral scent was shown to be most important for eliciting mating behaviour in males (Kullenberg 1961, Schiestl & al. 1999, Ayasse & al. 2003). Pollination in Ophrys is highly specific and usually each Ophrys species attracts only one pollinator species (Paulus & Gack 1990). The high degree of specialization provides the means of reproductive isolation between the intercrossable Ophrys-species (Ehrendorfer 1980). The complex odour-bouquets released by the flowers are species-specific and often consist of more than 100 different chemical compounds (Borg-Karlson & al. 1985, Ayasse 2006). Speciation in Ophrys-orchids may be brought about by changes in the pollinator attracting floral scent. The attraction of a new pollinator may act as a pre-zygotic isolation barrier (Stebbins 1970, Paulus & Gack 1990, Soliva & al. 2001). We investigated three sympatrically occuring Ophrys-species on Sardinia. O. chestermanii and O. normanii are endemic and are both pollinated by males of the bumblebee B. vestalis. O. tenthredinifera is pollinated by Eucera nigrilabris. There are different opinions concerning the taxonomic status of O. normanii. It has been described as an actual hybrid between O. chestermanii and O. tenthredinifera (Wood 1983). Paulus & Gack (1995) suggested that it is an own species, that either has developed from a hybrid between O. chestermanii and O. normanii or that has evolved by radiation from O. tenthredinifera. By conducting behavioural-tests with B. vestalis males, performing gas chromatographic analyses and electrophysiological studies we wanted to identify pollinator attracting scent and to clarify the taxonomic status of O. normanii.
The orchid genus Epipactis is represented by 25 species in Europe (Richards 1982). Epipactis helleborine (L.) Crantz is the most common and widely distributed species of the genus (Wiefelspütz 1970), and is a prime example for wasp-flowers, because it is mainly pollinated by social wasps (Hymenoptera: Vespidae), like Vespula vulgaris and V. germanica (Müller 1873). Darwin (1888) already noticed that E. helleborine is almost exclusively ignored by bees and bumblebees, an observation that was confirmed in recent investigations (Keppert 2001). The flowers of E. helleborine show morphological, physiological and phenological adaptations to the visit and the pollination by Vespidae (Keppert 2001). They possess a reddish-brown or dirty purple coloration of the inflorescence (Keppert 2001), have relatively small, mostly bulbous blossoms with a broad entrance and bulbous widened, nectar-rich juice holders (Müller 1873, 1881; Schremmer 1962). Although there is much reported about wasp-pollinated flowers there is little known about the signals that are responsible for the attraction of wasps. Wiefelspütz (1970) proclaimed the statement that only the visual stimulus is responsible for the wasp attraction. Recently studies, however, assumed that odour is involved in the wasp attraction (Keppert 2001). Hölzler (2003) showed that the main attraction of the wasp-flower Epipactis for pollinators is its olfactory stimulus. It remains an unanswered question why E. helleborine flowers almost exclusively attracts social wasps, as opposed to bees and bumblebees. In this study we analysed the role of floral volatiles which are responsible for the specific attraction of social wasps. We supposed a mimicry-system in E. helleborine for the specific attraction of pollinators for the following reasons. So-called “green leaf volatiles” (GLVs) are emitted by plants while herbivorous insects, for example caterpillars, feed on them. GLVs thereby attract predators or parasitoids of the herbivorous insects (Dicke & Sabelis 1988; Turlings & al. 1990, 1995; Dicke & Vet 1999). Among the GLVs so far identified in former studies there are aldehydes, compounds that were also found in flower extracts of E. helleborine (Hölzler 2003). Therefore, we postulated that E. helleborine flowers produce GLVs in order to attract prey hunting social wasps for pollination. We performed bioassays and analysed flower odour gained to headspace-sampling using gas chromatography (GC), mass spectrometry (GC-MS) and gas chromatography coupled with electrophysiological analysis (GC-EAD) to investigate the hypothesis that E. helleborine flowers mimic “green leaf volatiles” (GLVs) to attract their pollinators.
Die Glucosinolate (GS) sind charakteristische sekundäre Pflanzeninhaltsstoffe, vorkommend in der Gruppe der Brassicaceae und anderen Familien der Ordnung Brassicales (Halkier & Gershenzon 2006). Bisher sind mehr als 120 verschiedene GS beschrieben, welche eine gemeinsame Grundstruktur mit variablem Seitenkettenrest kennzeichnet (Fahey et al. 2001). Je nach chemischer Natur der Seitenkette werden die GS in aliphatische, aromatische und Indolyl-GS unterteilt. Alle GS-enthaltenden Pflanzen besitzen zusätzlich räumlich getrennt von den GS hydrolysierende Enzyme, so genannte Myrosinasen. Erst nach Zellbeschädigung kommen die beiden Komponenten in Kontakt zueinander und weitere biologisch aktive Verbindungen wie z. B. Isothiocyanate und Nitrile werden freigesetzt (Rask et al. 2000). Das GS-Myrosinase-System ist ein effektives Abwehrsystem insbesondere gegenüber generalistischen Insekten, Pathogenen und Bakterien, allerdings dienen vielen spezialisierten Insekten diese Stoffe zur Wirtspflanzenfindung und -akzeptanz (Renwick 2002, Halkier & Gershenzon 2006). Die Modellpflanze Arabidopsis thaliana L. enthält als Vertreter der Brassicaceae GS als Fraßabwehrstoffe. In A. thaliana als auch in Brassica ist das aliphatische GS-Muster sehr variabel, wohingegen die Indolyl-GS weit verbreitet sind (Kliebenstein 2001, Li & Quiros 2002). Allerdings fehlen Studien zur Funktion dieser GS-Klassen innerhalb der Pflanzenresistenz gegenüber Phytophagenfraß. Deshalb wurden zwei A. thaliana -Mutanten mit verändertem aliphatischen bzw. Indolyl-GS-Profil im Vergleich zu Columbia WT auf die Wirtspflanzeneignung für drei verschieden spezialisierte Lepidoptera-Arten getestet.
Solitary bees are important pollinators of flowers. Besides nectar they collect pollen at flowers mainly to provide their larvae with food. Many bee species collect pollen only on a few closely related plant species (oligolecty) (Müller & al. 1997). Little is known about the visual and olfactorial signals they use for host-plant finding (Wcislo & Cane 1996). However, bees can olfactorily distinguish between different pollen species (von Frisch 1923), and a species-specific chemistry of pollen odour is known for some plant species (Bergström & al. 1995, Dobson & al. 1999). Further, it was shown that naïve oligolectic bees recognize their host-plant on the basis pollen volatiles (Dobson & Bergström 2000) and that flower-experienced bees could use pollen odours to assess pollen availability (Dobson & al. 1999). Besides scent, also visual cues are of relevance for host-plant finding, and bees orientate especially spectral contrasts. Biotests with dummy flowers revealed that colour contrast and not intensity and dominant wavelengths are influencing innate behavioural responses (Lunau 1990). Further it was shown that naïve bumblebees were most motivated to land on a flower when visual stimuli from the antheres are combined with olfactorial stimuli from the pollen (1992). We choose Osmia adunca P., which is highly specialized on Echium L., as a model to investigate the importance of floral cues for an oligolectic bee. Because bees learn to associate odours with reward more rapidly than visual cues (Menzel 1985), we hypothesize that scent plays a major role in attraction flower-experienced O. adunca females. We used gas chromatography to compare the scent of three Echium species with the scent of a closely related Anchusa species, and a spectrometer to compare the colour of the three Echium species. Additionally we conducted a biotest to determine the importance of visual and olfactorial signals of Echium for host-plant finding of experienced O. adunca females.
Die Entwicklung einer Population des Kalifornischen Blütenthrips (Frankliniella occidentalis) in neuen oder ungewohnten Kulturpflanzenbeständen ist häufig anfangs sehr verhalten, um dann schlagartig zu kulminieren. Nicht selten werden dadurch Bekämpfungsmaßnahmen zu spät eingeleitet, was sich nachteilig auf deren Erfolg auswirkt. Anhand eines standardisierten Biotests im Labor sollte der Einfluss von verschiedenen Wirtspflanzen auf die Populationsentwicklung des Schädlings betrachtet werden.
In agroecological research it has been appreciated only fairly recently that plant-insect interactions and other ecological processes depend on scales much larger than a single habitat (Wiens et al. 1997). Crop-pest interactions have mainly been studied on single pest species by focusing either on the impact of field parameters or on landscape structure but only rarely included both factors (Östman et al. 2001). Here we investigated how the abundances of three major insect pest species in oilseed rape (OSR) responded to field parameters and landscape characteristics at various spatial scales. Pest species considered in the current study include (i) ceutorhynchid stem weevils that lay eggs in leaf petioles or midribs of OSR plants while the larvae tunnel in the stems; (ii) pollen beetles that feed on pollen and destroy flower buds and (iii) brassica pod midge that lay eggs into OSR pods where the hatched larvae consume the seeds as well as tissue of the pod walls and cause the pods to split prematurely (Alford et al. 2003). Studying these different groups of pests is especially important because they attack different parts of the crop, use different habitats as overwintering sites and also differ in their mobility; with the exception of pollen beetles these pest species have never been studied in a landscape context. The specific objectives of this study were to determine (i) whether the major OSR pest species differ in their relation to field and landscape characteristics and (ii) at which spatial scales landscape variables are effective.
Agricultural intensification is a major threat to biological diversity worldwide. Land management activities enhancing landscape diversity are therefore regarded as a key strategy to halt species loss in cultural landscapes. Diverse and abundant communities of predatory arthropods, e.g. spiders (Araneae), have a high potential to suppress pest populations (Symondson et al. 2002) and could therefore contribute to allow reductions of pesticide use. Crop fields alone are usually not able to sustain diverse and individual-rich populations of predatory arthropods, because agricultural management results in disturbances and habitat deteriorations (harvest, soil cultivation, pesticide application) that kill or drive away large parts of the populations. Therefore semi-natural and perennial habitats in agricultural landscapes are considered to be of great importance for beneficial arthropods. On the one hand they offer refuge habitats in times when arable fields are hostile, e.g. fields with bare grounds during winter (Schmidt & Tscharntke 2005). On the other hand, viable populations of predatory arthropods in semi-natural habitats can serve as sources for (re-) colonisation of arable fields (Schmidt & Tscharntke 2005). Because of these exchanges between crop and non-crop areas it is important to include the surrounding landscape when investigating field-scale processes. We investigated the relations between spider assemblages in arable fields and the surrounding landscape in 29 fields of winter oilseed rape (OSR) in an agricultural landscape in eastern Austria. The objectives of this study were to estimate (1) how much spider assemblages in oilseed rape fields are influenced by the surrounding landscape, (2) the relative influence of landscape variables compared to field-scale variables and (3) at which spatial scales landscape variables are effective.
The lower wood-feeding Australian termite Mastotermes darwiniensis Froggatt (Fig. 1) is the only living member of the family Mastotermitidae. The complex symbiotic hindgut flora consists of protozoa (formerly named Archaezoa; Cleveland & Grimstone 1964; Brugerolle & al. 1994; Berchtold & König 1995; Fröhlich & König 1999a, b), bacteria (Berchtold & König 1996; Berchtold & al. 1999), archaea (Fröhlich & König 1999a, b) and yeasts (Prillinger & al. 1996; Schäfer & al. 1996). The digestive system of Mastotermes darwiniensis consists of the foregut with the crop and the gizzard, the midgut, and the hindgut (Noirot & Noirot-Timothée 1969; 1995). The hindgut consists of five segments (P1 – P5): the proctodeal segment, the enteric valve, the paunch, the colon and the rectum. The paunch is the main microbial fermentation chamber, but the colon also contains microorganisms. The paunch is subdivided into a dilated thin-walled region (P3a) and a thick walled more tubular region (P3b) (Fig. 1c). In the case of Mastotermes darwiniensis oxygen diffusion gradients could be detected up to 100 μm below the epithelium (Berchtold & al., 1999).