Research on aboveground-belowground interactions has recently experienced a boost. In spite of the relative prosperity of scientific literature featuring aboveground herbivorous arthropods involved in aboveground-belowground interactions, mites have so far been under-represented. To stimulate work with mites in this area, we summarize existing research on plant-mediated interactions of aboveground herbivorous mites and belowground plant-associated organisms. A literature search revealed 17 studies dealing with plant-inhabiting mites, all of which involve the two-spotted spider mite Tetranychus urticae. We categorize the studies according to the belowground biota associated with the mite's host plants, summarize the observed effects of the belowground organisms on the aboveground mites and discuss possible interaction mechanisms. The paucity of existing studies does not yet allow one to draw general conclusions but it is apparent that these aboveground-belowground interactions are strongly context-dependent and vary among plant species and species of belowground biota. In conclusion, we argue that the wealth of knowledge on the behavior, ecology, physiology, and genetic make-up of T. urticae and its natural enemies, and ability to easily rear and perform experimental studies on this species at various spatial scales and organizational levels, make these plant-inhabiting mites perfectly-suited model organisms for future research on aboveground-belowground interactions.

Summary1. Indirect induced plant defence via emission of herbivore‐induced plant volatiles (HIPV) to recruit natural enemies of herbivores is a ubiquitous phenomenon, but whether and how emission of above‐ground HIPVs is adaptively modulated by below‐ground mutualistic micro‐organisms is unknown.2. We investigated the effects of the mycorrhizal fungus Glomus mosseae on chemical composition of HIPVs emitted by bean plants Phaseolus vulgaris attacked by spider mites, Tetranychus urticae, using proton‐transfer mass spectrometry, and attraction of the spider mites’ natural enemy, the predatory mite Phytoseiulus persimilis, to these HIPVs using a Y‐tube olfactometer.3. Mycorrhiza significantly changed the HIPV composition. Most notably, it increased the emission of β‐ocimene and β‐caryophyllene, two compounds synthesized de novo upon spider mite attack. The constitutively emitted methyl salicylate was increased by spider mite infestation but decreased by mycorrhiza.4. The predators responded strongly to HIPVs emitted by plants infested for 6 days and preferred HIPVs of mycorrhizal plants to those of non‐mycorrhizal plants. In contrast, they were less responsive and indiscriminative to mycorrhization when exposed to volatiles emitted by non‐infested plants and plants infested by spider mites for 1 or 3 days.5. Our study provides a key example of an adaptive indirect HIPV‐mediated interaction of a below‐ground micro‐organism with an above‐ground carnivore.

Root herbivores can influence both the performance and the behaviour of parasitoids of aboveground insect herbivores through changes in aboveground plant quality and in the composition of the plant's odour blend. Here we show that root herbivory by Delia radicum larvae did not influence the innate preferences for plant odours of the two closely related parasitoid species Cotesia glomerata and C. rubecula, but did affect their learned preferences, and did so in an opposite direction. While C. glomerata learned to prefer the odour of plants with intact roots, C. rubecula learned to prefer the odour of root-infested plants. The learned preference of C. glomerata for the odour of plants with intact roots matches our previously published result of its better performance when developing in P. brassicae hosts feeding on this plant type. In contrast, the relatively stronger learned preference of C. rubecula for the odour of root-infested plants cannot be merely explained by its performance, as the results of our present study indicate that D. radicum root herbivory did not influence the performance of C. rubecula nor of its host P. rapae. Our results stress the importance of assessing the influence of root herbivores on both innate and learned responses of parasitoids to plant odours.

Research on trophic cascades in terrestrial ecosystems has only recently revealed that root-associated organisms interact with organisms living on aboveground plant parts. Arbuscular mycorrhizal (AM) symbiosis is a ubiquitous phenomenon, yet studies on its effect on aboveground natural enemies of herbivores are scarce and mainly deal with plant-mediated rather than herbivore-mediated interactions. Here, we studied herbivore-mediated effects of AM symbiosis on an acarine predator. We measured life history characteristics and population growth rates of Phytoseiulus persimilis preying on two-spotted spider mites, Tetranychus urticae, which were feeding on bean plants colonized or not colonized by the AM fungus Glomus mosseae. All major life history characteristics of P. persimilis, foremost oviposition rate, minimum prey requirements needed to reach adulthood, and developmental time, were positively affected by AM colonization of the host plant of their prey, together resulting in enhanced population growth rates of the predators. Hence, we hypothesize that a bottom-up trophic cascade may counteract the apparent negative effects of mycorrhizal symbiosis when promoting herbivory by promoting the predation of herbivores due to improved prey quality. We argue that this pathway may be involved in stabilizing plant–mycorrhizal symbiosis in ecosystems over time.

1. Arbuscular mycorrhiza (AM), the association of AM fungi and plant roots, may alter morphological and physiological attributes of aboveground plant parts and thereby influence plant‐associated organisms such as herbivores and their natural enemies, predators and parasitoids.2. The interactions between AM and the players of aboveground tri‐trophic systems have mainly been considered in isolation from each other. The effects of AM on aboveground herbivore–carnivore population dynamics and the consequences to plant fitness are unknown.3. We explored AM‐induced compensatory mechanisms for AM‐promoted proliferation of the herbivorous spider mite, Tetranychus urticae Koch, on whole bean plants, Phaseolus vulgaris L. Vegetative and reproductive plant growth, AM fungal colonisation levels, and mite densities were assessed on spider mite‐infested plants colonised or not by the AM fungus Glomus mosseae Nicol. & Gerd, and harbouring the natural enemy of the spider mites, the predatory mite Phytoseiulus persimilis Anthias‐Henriot or not.4. AM symbiosis modulated the aboveground tri‐trophic system to the fitness benefit of the plant. AM‐increased plant productivity outweighed the fitness decrease due to AM‐promoted herbivory: at similar vegetative growth, mycorrhizal plants produced more seeds than non‐mycorrhizal plants.5. AM‐increased spider mite population levels were compensated for by enhanced population growth of the predators and increased plant tolerance to herbivory.6. AM‐enhanced predator performance looped back to the AM fungus and stabilised its root colonisation levels, providing the first experimental evidence of a mutually beneficial interaction between AM and an aboveground third trophic level natural enemy.

Most terrestrial plants are associated with arbuscular mycorrhizal fungi but research on the effects of arbuscular mycorrhizal symbiosis on aboveground plant‐associated organisms is scarcely expanded to tri‐trophic systems. The arbuscular mycorrhizal fungus Glomus mosseae Nicol. & Gerd. enhances fitness of the two‐spotted spider mite Tetranychus urticae Koch and its natural enemy, the predatory mite Phytoseiulus persimilis Athias‐Henriot, via changes in host plant and prey quality, respectively. In the present study, it is hypothesized that gravid P. persimilis are able to recognize arbuscular mycorrhiza‐enhanced prey quality and behave accordingly. In two experiments, on leaf arenas and in cages, P. persimilis is given a choice between prey patches deriving from mycorrhizal and non‐mycorrhizal bean plants (Phaseolus vulgaris L.) as feeding and oviposition sites. The use of cages allows the manipulation of distinct patch components acting as possible cues to guide predator foraging and oviposition behaviours, such as eggs produced and traces (webbing and faeces) left by the spider mite females. Both experiments show that P. persimilis preferentially resides close to prey fed on mycorrhizal plants. The cage experiment reveals that P. persimilis uses direct prey‐related cues, mainly derived from eggs, to discern prey quality and preferentially oviposits close to prey from mycorrhizal plants. This is the first study to document that predators recognize arbuscular mycorrhiza‐induced changes in herbivorous prey quality via direct prey‐related cues.

A new steering concept for laser-driven parabolic thrusters is presented. As an alternative to the well-tried spin-stabilization, our concept provides rocket stabilization and trajectory control and is suitable for the injection of a laser-driven launcher into a planetary orbit: Angular and lateral momentum components are systematically applied to the rocket by specific variation of the ignition configuration inside the parabolic thruster. The effect of the tilting angle of the steering gear from the axis of symmetry on momentum coupling is examined, as well as the influences of pulse energy and ignition geometry. Based on the experimental results, an off-axis detonation is modeled with respect to the fluence distribution at the ignition area and the resulting force components. A demonstrator model of a laser-driven rocket with a parabolic thruster has been constructed, including a remotely controlled steering gear and a separate payload fraction. Test flights employing a high energy CO2 laser have been performed successfully.

Learning is a ubiquitous phenomenon in foraging animals, allowing behavioural optimisation in variable environments. Food imprinting is a specific form of learning restricted to the early stages of life and with long lasting consequences. However, since coining of the term four decades ago, the uniqueness of food imprinting has been largely questioned due to a putative mechanistic similarity with associative learning. Here, we demonstrate food imprinting in the predatory mite Neoseiulus californicus , which primarily feeds on spider mites but may use thrips as alternative prey. Brief (24 h) exposure to thrips (contact without feeding) early in life resulted in shorter attack latencies and consistently higher predation rates on thrips during adulthood. Predation and oviposition rates were positively correlated but oviposition did not differ between naive and experienced females. Our results suggest that food imprinting is indeed special because, unlike associative learning, it occurred without reinforcement, was restricted to a sensitive phase and persisted into adulthood. Food imprinting seems particularly advantageous when prey species availability varies little within generations and a given prey is difficult to ingest for young small but not older larger life stages. Food imprintability could be used to improve the efficacy of biocontrol agents such as N. californicus .

The two-spotted spider mite, Tetranychus urticae, is one of the most problematic phytophagous pests in Spanish clementine orchards. The most abundant predatory mites in this ecosystem are Euseius stipulatus, Phytoseiulus persimilis and Neoseiulus californicus. Euseius stipulatus is dominant but poorly adapted to utilize T. urticae as prey. It mainly persists on pollen and citrus red mite, Panonychus citri. A recent study suggested that the more efficacious T. urticae predators P. persimilis and N. californicus are negatively affected by lethal and non-lethal intraguild interactions with E. stipulatus. Here, we investigated the potential of N. californicus and P. persimilis to colonize and thrive on young clementine trees infested by T. urticae in presence and absence of E. stipulatus. Presence of E. stipulatus interfered with establishment and abundance of P. persimilis and negatively affected the efficacy of N. californicus in T. urticae suppression. In contrast, the abundance of E. stipulatus was not affected by introduction of a second predator. Trait-mediated effects of E. stipulatus changing P. persimilis and N. californicus behavior and/or life history were the most likely explanations for these outcomes. We conclude that superiority of E. stipulatus in intraguild interactions may indeed contribute to the currently observed predator species composition and abundance, rendering natural control of T. urticae in Spanish clementine orchards unsatisfactory. Nonetheless, stronger reduction of T. urticae and/or plant damage in the predator combination treatments as compared to E. stipulatus alone indicates the possibility to improve T. urticae control via repeated releases of N. californicus and/or P. persimilis.

Ein Demonstrationsmodell fur einen Raumfahrtantrieb mit einem Hochenergielaser als separater, stationarer Energiequelle wird untersucht. Dazu wird ein leichter parabolischer Reflektor eingesetzt. Er dient zur Fokussierung der gepulsten CO 2 -Laserstrahlung und als Expansionsduse fur das erhitzte Gas aus der laser-induzierten Plasmadetonation. Zeitlich hochaufgeloste Videoaufnahmen und Entfernungsmessungen erlauben die Analyse von Trajektorien aus gepulsten Flugexperimenten. Der Impulsubertrag auf den Reflektor wird analysiert und im Hinblick auf Regelungsmoglichkeiten im Sinne einer Schubvektorsteuerung bewertet.

High energy pulses of a CO2 laser are focused in a parabolic mirror yielding to a laser-supported detonation. The generated thrust acting on the reflector as a bell nozzle is studied in multiple pulse free flight experiments with respect to axial, lateral and angular momentum coupling. The employment of an ignition pin on the reflector's axis of symmetry lowering the ignition threshold by several orders of magnitude is found to provide for a reproducible detonation process. The axial momentum coupling of each pulse is analyzed with respect to initial lateral offset and tilt during the flight. High speed analyses of recorded flights indicate that lateral momentum components occur re-centering the thruster on the beam. Thrust vector steering can be realized by tilt of the ignition pin inside the thruster, thus shifting the detonation. A design model of a laser-driven rocket including a remotely accessible steering gear was developed and tested successfully.

Most terrestrial plants live in symbiosis with arbuscular mycorrhizal (AM) fungi. Studies on the direct interaction between plants and mycorrhizal fungi are numerous whereas studies on the indirect interaction between such fungi and herbivores feeding on aboveground plant parts are scarce. We studied the impact of AM symbiosis on host plant choice and life history of an acarine surface piercing-sucking herbivore, the polyphagous two-spotted spider mite Tetranychus urticae. Experiments were performed on detached leaflets taken from common bean plants (Phaseolus vulgaris) colonized or not colonized by the AM fungus Glomus mosseae. T. urticae females were subjected to choice tests between leaves from mycorrhizal and non-mycorrhizal plants. Juvenile survival and development, adult female survival, oviposition rate and offspring sex ratio were measured in order to estimate the population growth parameters of T. urticae on either substrate. Moreover, we analyzed the macro- and micronutrient concentration of the aboveground plant parts. Adult T. urticae females preferentially resided and oviposited on mycorrhizal versus non-mycorrhizal leaflets. AM symbiosis significantly decreased embryonic development time and increased the overall oviposition rate as well as the proportion of female offspring produced during peak oviposition. Altogether, the improved life history parameters resulted in significant changes in net reproductive rate, intrinsic rate of increase, doubling time and finite rate of increase. Aboveground parts of colonized plants showed higher concentrations of P and K whereas Mn and Zn were both found at lower levels. This is the first study documenting the effect of AM symbiosis on the population growth rates of a herbivore, tracking the changes in life history characteristics throughout the life cycle. We discuss the AM-plant-herbivore interaction in relation to plant quality, herbivore feeding type and site and the evolutionary implications in a multi-trophic context.

Ein Zukunftskonzept fur Raketenantrieb ist der Laserantrieb. Die Idee eines Laserantriebes existiert seit den 70er Jahren als A. Kantrowitz die Idee entwickelte die Energie von hochenergetischem Laserlicht zu nutzen um von einer externen Quelle (z.B. am Erdboden) Schub in einer Luft atmenden Rakete zu erzeugen. An dieser Idee wurde seit dem weitergearbeitet, sowohl experimentell als auch konzeptionell. Der heutige Stand der Dinge ist, dass Fluge bereits realisiert worden sind, wenn auch nur vertikale Fluge von begrenzter Hohe, wahrend die Anwendungskonzepte solcher Antriebe schon ausgereift sind. Den Forschergruppen mangelte es lange an geeigneten Lasern. Doch seit etwa 20 Jahren tut sich einiges, um solche Antrieb in ferner Zukunft anwenden zu konnen. Besonders interessant ist dieses Antriebskonzept im Hinblick auf die gegenwartige Entwicklung in der Weltraumnutzung: Die Anzahl der Satelliten wachst; vor allem Dank kleiner Forschungssatelliten gebaut von einer Vielzahl von offentlich und privaten Forschungseinrichtungen. Gerade fur solch kleine Satelliten wie die „Nanosatelliten“, die gerade mal ein Gewicht von 1-10 kg aufbringen, konnte das Konzept des Laserantriebs geeignet sein. Eine Laserrakete bundelt mittels eines parabolischen Reflektors parallel ankommende Lichtstrahlen in einem Fokuspunkt. Die Intensitat der elektromagnetischen Strahlung in diesem Punkt ist so hoch, dass die Temperatur der den Reflektor fullenden Luft derart ansteigt, dass sie in ein sogenanntes Plasma dissoziiert. Plasma ist ein Gasgemisch aus Ionen und Elektronen. Dabei kann der Laser gepulst oder konstant betrieben werden, wobei in dieser Arbeit mit einem gepulsten Laser gearbeitet wurde. Die Detonation verursacht eine Schockwelle, welche von den Wanden des parabolischen Reflektors in Richtung des ankommenden Laserlichts reflektiert wird. Die reflektierte Schockwelle ubertragt einen Gegenimpuls auf die Laserrakete. Diese wird senkrecht nach oben beschleunigt. Durch Verwendung eines sogenannten Zundstifts, der entlang der Symmetrieachse des parabolischen Reflektors platziert wird, der der sonst raumlich schwankende Zundort stabilisiert werden. Durch Verwendung eines Festtreibstoffes, welcher auf den Zundstift geschraubt wird, kann zusatzlicher Schub erzeugt werden.Steuerungskonzepte fur Laserraketen wurden bislang noch nicht experimentell ausgewertet. In dieser Diplomarbeit soll daher die Funktionalitat eines der Konzepte erforscht werden. Das Konzept einer Schubvektorsteuerung basiert auf der Idee, durch gezieltes Verschieben des Zundortes weg von der Symmetrielinie des parabolischen Reflektors, eine asymmetrische Ausbreitung der Schockwelle und somit einen asymmetrischen Schubvektor und eine Drehung um den Schwerpunkt zu erzeugen. Die gezielte Verschiebung des Zundortes soll mittels Kippen des Zundstiftes um den Scheitel des parabolischen Reflektors erfolgen. Um das Konzept zu testen wurden parabolische Reflektoren, die am DLR bereits, sowohl mit als auch ohne Treibstoff, fur vertikale Fluge verwendet wurden, mit schraggestellten Zundstiften verschiedener Winkel versehen. Im Rahmen dieser Arbeit wurden die Effekte auf Flugeigenschaften, wie die Impulse in vertikaler, horizontaler und rotatorischer Richtung und wie der Flug- und Drehwinkel untersucht. Dazu wurden drei verschiedene Treibstoffgrosen, drei verschiedene Zundstiftwinkel, drei verschieden Energiebereiche und vier verschiedene Frequenzbereiche getestet. Zusammenhange zwischen den Vorgabeparametern und den Reaktionen des parabolischen Reflektors wurden untersucht und versucht zu entschlusseln. Dabei wurde beobachtet, dass eine Steuerung zwar funktioniert, die Reaktionen aber teilweise unerwartet waren. Durch Verwendung eines Treibstoffes verkomplizieren sich die Impuls gebenden Vorgange wahrend des Beschleunigungsprozesses. Um in Zukunft ein experimentelles Arbeiten mit Variablen Treibstoffwinkeln zu ermoglichen, sollte ein Labormodell entwickelt werden, welches einen fernansteuerbaren Stellmechanismus and den parabolischen Reflektor koppelt und Raum fur Testnutzlasten integriert. Diese Laserrakete musste verschiedene Bedingungen erfullen, die eine Konstruktion nicht einfach machten. Durch die Begrenzte Leistung des Lasers, durfte eine bestimmte Masse nicht uberschritten werden. Die geschatzte Grenze lag bei etwa 200 g, dabei wiegen die parabolischen Reflektoren die bislang eingesetzt worden sind bereits bei etwa 15–30 g. Nachdem die benotigten Komponenten grob definiert wurden, wurde eine umfangreiche Komponentenrecherche durchgefuhrt.Ergebnis dieser Recherche war, dass fur die Komponenten fur die Steuerung auf den Modellbau zuruckgegriffen wird und die Flugkorper Hulle aus Plastik hergestellt werden muss. Alles musste dabei so ausgelegt werden, dass die enormen Belastungen bei der Beschleunigung der Rakete bei einem Laserpuls die Teile und Verbindungen nicht zerstoren. Nach Fertigstellung und Lieferung aller konstruierten und bestellten Teile, wurde die Laserrakete auf Flugtauglichkeit, Funktionalitat und Robustheit gepruft. Ergebnis der Testfluge ist, dass die Mechanik, die Elektronik und alle Verbindungen halten und funktionieren, was aufgrund der starken Schocks und der elektromagnetischen Strahlung nicht selbstverstandlich ist. Beeindruckend ist auch die Lenkbarkeit. Trotz der geringen Flughohe die nur durch das hohe Gewicht und die mangelnde Laserleistung erreicht werden konnte, ist eine eindeutige Steuerung sichtbar.