Modellentwicklung für ein Entscheidungsunterstützungssystem für den optimalen Einsatz von Pestiziden in der Baumwollproduktion

In this thesis, we proposed and described well organized materials for the development of a Decision Support System aiming at the optimal allocation of pesticides in agriculture, given that resistance can develop in the target population, and pesticides environmental pollution, mainly water resources, can occur. These materials are a collection of mathematical sub-models, simulating the dynamics of crops and pests and the environmental fate of pesticides. Different mathematical approaches were used: continuous time models in the form of ordinary differential equations for the growth of cotton crop and for the kinetics of insecticides; in the form of partial differential equations for the spatial spread of pests and pesticides in soil and a discrete time model for population dynamics of age and stage structured populations. For the cotton crop dynamics sub-model, parameter estimation was carried out based on literature data. The Decision Support System was then constructed by integrating the sub-models. The models were implemented in the numerical programming environment Matlab. For the solutions of the partial differential equations, the finite elements tool COMSOL Multiphysics was used. Various tests were carried out to verify the model behavior for plausibility: syntax check, stress tests with extreme parameters values and comparison with measured data. The behavior of the model with respect to parameters variations followed expected trends. Using a suitable objective function, control measures were evaluated including economic criteria with fictive environmental costs. The application of the integrated model to the development of better management practices for the control of the cotton pest Helocoverpa armigera in the growing areas of Burkina Faso led to substantial modifications of the usual practical method. However, more tests and applications are necessary in different production areas to effectively transfer the method presented here to other crops and pests.In dieser Arbeit beschreibe ich die Entwicklung eines Entscheidungsunterstützungs-Systems mit dem Ziel der optimierten Verwendung von Pestiziden in der Landwirtschaft, um das Risiko für das Auftreten von Resistenzen bei den Zielorganismen und die Verschmutzung von Wasserressourcen zu minimieren. Die dafür verwendeten Methoden sind eine Sammlung mathematischer Teilmodelle für die Simulation der Dynamik von Kulturpflanzen und Schädlingen und des Umweltverhaltens von Pestiziden. Dabei wurden unterschiedliche mathematische Ansätze verwendet: zeitkontinuierliche Modelle in Form eines Systems von gewöhnlichen Differentialgleichungen für das Wachstum von Baumwollkulturen und für die Kinetik von Insektiziden und in Form von partiellen Differentialgleichungen für die räumliche Ausbreitung von Schädlingen und Pestiziden in Böden sowie ein zeitdiskretes Modell für die Populationsdynamik von alters- und stadienstrukturierten Populationen. Die Teilmodelle wurden separat getestet, um sie zu verifizieren. Für das Teilmodell für die Bestandesdynamik von Baumwolle konnte anhand von Literaturdaten eine Parameteridentifikation durchgeführt werden. Das Entscheidungsunterstützungs-System ergab sich dann aus der Integration der Teilmodelle. Die Modelle wurden in die numerischen Programmierumgebung Matlab implementiert. Für die Lösung der partiellen Differentialgleichungen wurde das Finite-Elemente-Tool COMSOL Multiphysics verwendet. Verschiedene Tests wurden durchgeführt, um das Modellverhalten auf Plausibilität zu überprüfen: Syntaxprüfung, Stresstests mit extremen Parameterwerten und Vergleich mit Messdaten. Das Verhalten des Modells in Bezug auf die Parameter-Variationen folgte den erwarteten Trends. Anhand einer geeigneten Zielfunktion, die ökonomische Kriterien mit fiktiven Umweltkosten verknüpft, wurden Kontrollmaßnahmen bewertet. Die Anwendung des integrierten Modells auf die Entwicklung optimaler Managementverfahren zur Bekämpfung des Baumwollschädlings Helocoverpa armigera im Anbaugebiet von Burkina Faso führte zu erheblichen Modifikationen der praxisüblichen Verfahren. Jedoch sind mehr Tests und Anwendungen in verschiedenen Anbaugebieten notwendig, um die hier vorgestellte Methode effektiv auf andere Kulturen und Schädlinge zu übertragen

Invasion Impact and Biotic Resistance by Invertebrate Communities

Invasive species have been recognized as one of the greatest threats to global biodiversity and can have dire economic consequences. Yet rates of invasion are increasing due to the fast and growing network of transportation across the globe. The establishment, spread and impact of invasive species are affected by environmental conditions as well as resident species. Species respond differently to the same abiotic factors and different native species can respond either positively or negatively to invasion. The interaction between invasive and resident species, as well as the effect of temperature on invasive species, has gained much attention. The synergistic effect of suboptimal temperature and biotic resistance could have a much stronger limiting or controlling effect on invasive species than either factor alone. Linepithema humile (Argentine ants) are invasive species originally from a Mediterranean climate, but successfully spreading into extra range habitats. The establishment and spread of these ants in temperate New Zealand represents an ideal model system for studying invasion biology in terms of temperature limits and biotic resistance effects. I investigated the changing distribution of the invasive species the Argentine ants over multiple years at five sites in New Zealand. To test whether their rate of spread corresponds with microclimate I investigated their fine-scare distribution patterns and evaluated the number of generations they may develop seasonally and annually in different microhabitat types. I also evaluated their impact on other arthropod species. I conducted a laboratory experiment to evaluate the effect of temperature on their aggression towards other species, walking speed, and foraging abundance. Similarly, I tested the effect of biotic resistance from other ant species (Monomorium antarcticum and Prolasius advenus) with varying colony sizes. I investigated whether there was any interactive effect of temperature and biotic resistance on the Argentine ants. The distribution of Argentine ants had declined across many invasion fronts over the past 7-8 years. They were more likely to be found in concrete, short grass and sandy habitats, which provide warm microsites. Degree-day calculations predicted that they could develop between 2.5 to 3 generations in each of the above microhabitats per year in urban and rural sites while they were predicted to be unable to develop one generation under tree habitats. In tall grass microhabitats they were predicted to develop between 1-1.5 generations per year. The Argentine ants were hypothesised to adversely affect many other arthropod species. Richness and abundance of resident beetle species were negatively correlated with the invasion of the Argentine ants. Areas invaded by the Argentine ants were also associated with a greater number of exotic beetle species, which may imply secondary invasion. Laboratory experiments showed that lowering temperatures below 17°C negatively affected the Argentine ants‟ walking speed, foraging abundance, aggression and their resource control. A high colony size of M. antarcticum (the competing ant species) affected the foraging success of Argentine ants, and the effect was stronger when coupled with unsuitable temperature (17°C and below). Therefore, Argentine ants are weak competitors at low temperature levels. The results of my thesis underline the importance of biotic and abiotic resistances, their interactive effect as well as the effect of the Argentine ants on other species. Based on climatic considerations and the habitat preferences of resident species it may be possible to predict future spread of the Argentine ants. More importantly, knowledge of microhabitat preferences and biotic resistance may help future control measures against Argentine ants based on management of vegetation structure and microhabitat availability