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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
21

Host plant selection in closely related butterfly species due to reproductive interference: Modelling a tritrophic system

Bantounas, Alexandros January 2021 (has links)
Host plant selection is an important process during the life cycle of lepidopterans, providing ovipositing sites for adults and food resources for the larvae. The processes behind host plant selection have been extensively studied, especially in closely related species in the context of niche separation. Empirical and theoretical studies have shown that multiple processes, such as resource competition, parasitoid avoidance and reproductive interference between interspecific individuals can affect host plant selection, often leading to niche separation. The aim of this study was to create and analyze a mathematical model using the adaptive dynamics techniques, in order to study the evolution of habitat selection. Our model incorporated three processes: Resource competition in the form of density dependent growth, parasitoid attacks and repro- ductive interference in a two species-two habitat system. It was hypothesized that the presence of parasitoids would promote co-existence through top-down control, while reproductive inter- ference would promote niche separation. The results confirmed both hypotheses. The analysis incorporating only the effect of parasitism showed the evolution of habitat separation when parasitoids attacked randomly and the evolution of co-existence in both habitats in the case of switching parasitoids. On the other hand, incorporating reproductive interference promoted the evolution of partial or complete niche separation. The extent of this process was shown to depend on the strength of reproductive interference and the initial habitat choice of the two species. Stronger reproductive interference increased the size of the set of initial conditions leading to the evolution of complete niche separation. The analysis conducted in this study demonstrated the opposing effects of parasitism and reproductive interference on the evolution of habitat selection, promoting co-existence and separation respectively.
22

Oxidation of plant allelochemicals by phytophagous sucking insects

Lorraine, Debrah F. January 1995 (has links) (PDF)
Addendum in pocket. Biblography: leaves 162-173. Phytophagous sucking insects, aphids in particular, are common pests of plants. These insects secrete salivary enzymes into their food material. One plant defence mechanism is the induction and/or accumulation of deterrent phytochemicals. In the present study, a model enzyme system was chosen to mimic the oxidative activity of insect saliva. Isolation and sructural identification of the products of plant allelochemicals was achieved for several substrates. Insects were also exposed to individual plant chemicals in feeding "choice" tests. Preliminary examinations suggest that plants containing increased levels of phenolic allelochemicals show correlated increases in resistance to attack by aphids.
23

Oxidation of plant allelochemicals by phytophagous sucking insects / by Debrah F. Lorraine.

Lorraine, Debrah F. January 1995 (has links)
Addendum in pocket. / Biblography: leaves 162-173. / v, 177, [5] leaves : ill. ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Phytophagous sucking insects, aphids in particular, are common pests of plants. These insects secrete salivary enzymes into their food material. One plant defence mechanism is the induction and/or accumulation of deterrent phytochemicals. In the present study, a model enzyme system was chosen to mimic the oxidative activity of insect saliva. Isolation and sructural identification of the products of plant allelochemicals was achieved for several substrates. Insects were also exposed to individual plant chemicals in feeding "choice" tests. Preliminary examinations suggest that plants containing increased levels of phenolic allelochemicals show correlated increases in resistance to attack by aphids. / Thesis (Ph.D.)--University of Adelaide, Dept. of Crop Protection, 1996
24

The effect on phytophagous insects of variations in defence mechanisms within a plant

West, Christopher January 1985 (has links)
No description available.
25

Etude de l'histoire évolutive d'insectes phytophages: approche phylogéographique et développements méthodologiques

Dellicour, Simon 04 December 2013 (has links)
Doctorat en Sciences / info:eu-repo/semantics/nonPublished
26

When and where to lay your eggs?

Köhncke, Arnulf 26 September 2013 (has links)
Bei der Eiablage müssen sich Pflanzen fressende Insekten wiederholt entscheiden, Eier auf Wirtspflanzen niedriger Qualität zu legen oder auf bessere Pflanzen zu warten. Diese Entscheidungen sind Fitness relevant, weil Larven sich je nach Wirt unterschiedlich entwickeln und weil Weibchen in diesem inter-temporären Optimierungsproblem sowohl zu wählerisch als auch nicht wählerisch genug sein und so nicht alle Eier bzw. Eier in zu geringer Qualität legen können. Meine Arbeit nutzt vier Ansätze um zu untersuchen, wie diese Entscheidungsprobleme entstehen und wie Weibchen diese strategisch lösen. Erstens benutze ich analytische Optimierungsmodelle um zu zeigen, dass ein evolutionärer Trade-Off zwischen Vermehrung und Überleben variierender evolutionär stabiler Ei- und Zeit-Limitierung führen kann, dass aber keiner dieser zwei Faktoren ignoriert werden darf. Zweitens stelle ich klar, dass in der Vergangenheit vorgeschlagene schematische Zeit- und Ei-Kosten der Eiablage sich nicht mit den wirklichen Selektionskräften auf die Ei-Anzahl decken und daher kein gutes Werkzeug zur Analyse von Eiablage-Strategien darstellen. Drittens zeige ich mit Optimierungs- und populationsgenetischen Modellen, dass räumliche Heterogenität in der Wirtsverfügbarkeit keine notwendige Bedingung für die Evolution von Generalismus ist, weil emergente Quellen-Senken Dynamiken die Anpassung der Insekten an marginale Habitate verhindern, wenn Migrationsraten nicht hoch sind. Viertens zeige ich an Agenten basierte Simulationen zum Beispiel des Aurorafalters, Anthocharis cardamines, dass der phänologische Spezialismus der Larven dieser Art den Eiablage-Generalismus der Weibchen zur Folge hat. Insgesamt zeigen diese vier Ergebnisse, wie nützlich theoretische Ansätze zur Untersuchung spezifischer Szenarios der strategischen Eiablage sein können und machen deutlich, dass die Evolution von Generalismus leichter aus zeitlicher denn aus räumlicher Heterogenität folgt. / Ovipositing phytophagous insects repeatedly face the decision problem of laying eggs on lower-quality host plants or waiting out for higher-quality ones. These choices carry fitness costs and benefits because larvae develop differentially on different hosts and because, in this inter-temporal optimization task, females may be too choosy and die before laying all eggs (i.e. become time-limited) or not be choosy enough and run out of eggs before their death (i.e. become egg-limited). This thesis employs four approaches to examine how oviposition decision problems arise and how they are strategically solved by female insects. First, I use analytical optimization models to show that a life-history trade-off between survival and reproduction can lead to varying evolutionarily stable levels of egg and time limitation, but that neither egg nor time limitation can be ignored in evolutionary analyses of oviposition. Second, I highlight that such schematic time and egg costs of oviposition as advocated in the past do not match the actual forces of natural selection on egg number as partitioned between egg and time limitation and therefore represent a less useful practice to analyze oviposition strategies. Third, I use optimality and population genetic models to show that spatial heterogeneity in host availability is not a sufficient condition for the evolution of generalism because emergent source-sink dynamics preclude adaptation of insects to marginal habitats unless migration rates are high. Fourth, I employ individual-based simulations built around the case study of the orange tip butterfly, Anthocharis cardamines, to show that this species’ larvae’s phenological specialism may drive the adult females’ oviposition generalism. All these findings show the usefulness of theoretical approaches to examine specific questions of strategic oviposition. Moreover, they demonstrate that evolution of generalism more likely results from resource unpredictability in time than in space.
27

Drivers of macrophyte assemblages in South African freshwater systems

Martin, Grant Douglas January 2013 (has links)
Potentially damaging submerged invasive freshwater macrophytes have been identified in South African freshwater systems, but have received less attention than their floating counterparts. To ascertain the changes and effects that these species may have on macrophyte ecology, an understanding of the drivers of macrophyte assemblages is essential. The aims of this thesis were to investigate select abiotic and biotic factors driving introduction, establishment and spread of submerged macrophytes in South Africa. Surveys on the status of submerged plant species in South Africa were conducted to find out the distribution and diversity of the species present, imported to, and traded in South Africa. Numerous submerged indigenous and invasive macrophyte locality records were collected during field surveys, of which many were first time records. Pet stores and aquarist trading activities were identified as potential vectors for the spread of submerged macrophytes through online surveys and personal interviews. These results highlighted the potential these species have for continuing to enter, and spread within South African water bodies. Maximum Entropy (MAXENT) is a general-purpose method used to predict or infer distributions from incomplete information, and was used here to predict areas suitable for the establishment of five of these invasive macrophytes. Many systems throughout South Africa, particularly those in the subtropical coastal regions, were found to be climatically suitable for the establishment of Elodea canadensis Michx., Egeria densa Planch., Hydrilla verticillata (L.f.) Royle (all Hydrocharitaceae), Myriophyllum spicatum L. (Haloragaceae), and Cabomba caroliniana Gray (Cabombaceae). Despite the high probability of invasion, facilitated by vectors and suitable climate, South Africa’s rich indigenous submerged aquatic flora may be preventing the establishment of these submerged invasive species. Studies on the competitive interactions between a common indigenous submerged macrophytes, Lagarosiphon major (Roxb.) (Hydrocharitaceae) and M.spicatum, an invasive native to Eurasia, were conducted to ascertain which conditions influence competitive superiority. High sediment nutrient conditions significantly increased the growth rate and competitive ability of both species, while clay sediments significantly increased the competitive ability of L. major over M. spicatum, but sandy sediments improved the competitive ability of M. spicatum. These results highlighted the dynamic changes in competition between submerged species driven by abiotic factors, but did not take into consideration the effect that herbivory, a biotic factor, could have on competition between the two species. The effect of herbivory by phytophagous insects of submerged plant species has been regarded as negligible. To find out what this effect is, multiple field surveys were undertaken throughout South Africa to find natural enemies of indigenous Lagarosiphon species with the aim of identifying such species, and quantifying their influence on plant growth dynamics. Several new phytophagous species were recorded for the first time. An ephydrid fly, Hydrellia lagarosiphon Deeming (Diptera: Ephydridae) was ascertained to be the most ubiquitous and abundant species associated with L. major in South Africa. The influence of herbivory by this fly on the competitive ability of L. major in the presence of M. spicatum was investigated using an inverse linear model, which showed that herbivory by H. lagarosiphon reduced the competitive ability of L. major by approximately five times in favour of M. spicatum. This study served to highlight the importance of herbivory as a driver of submerged aquatic plant dynamics. Current ecological theory emphasises the importance of investigating beyond plant-herbivore interactions, by including multitrophic interactions in community dynamics. Therefore, the potential of parasitism by a parasitoid wasp, Chaenusa luteostigma sp. n. Achterberg (Hymenoptera: Braconidae: Alysiinae) on H. lagarosiphon to shift the competitive interactions between the two plant species was also examined. The addition of the parasitoid reduced the effect of herbivory by the fly on L. major by half, thereby shifting the competitive balance in favour of L. major over M. spicatum. This study provides valuable insight into a selection of drivers of submerged macrophyte assemblages of South Africa. It highlights the precarious position of South African freshwater systems with regard to the potential invasion by damaging submerged invasive species. It also provides interesting insights into the effect of competition, herbivory and parasitism on the establishment and spread of species within submerged freshwater systems. Understanding the different influences could assist managers and policy makers to make validated decisions ensuring the integrity of South African freshwater systems.
28

Pflanze-Herbivore-Parasitoid Interaktionen auf Wildrosenarten und ihren Hybriden entlang eines geographischen Gradienten / Plant-herbivore-parasitoid interations on dog rose species and their hybrids along a geographic gradient

Klinge, Katrin 19 January 2006 (has links)
No description available.
29

Untersuchungen zum Einfluß des Kots phytophager Insekten auf die Keimung und das frühe Wachstum von Kiefern (Pinus sylvestris L.), Birken (Betula pendula Roth.) und Eichen (Quercus robur L.) unter besonderer Berücksichtigung des Inhaltsstoff-Musters der Blattorgane / Investigation of the influence of insectfrass on the germination and the early growth of young pines (Pinus sylvestris L.), birches (Betula pendula Roth.) and oaks (Quercus robur L.) - especially on the patterns of the nutrients and inhibitors in the needles and leaves

Jung, Peter 22 October 2004 (has links)
No description available.
30

Birds, bats and arthropods in tropical agroforestry landscapes: Functional diversity, multitrophic interactions and crop yield

Maas, Bea 20 November 2013 (has links)
No description available.

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