Browsing by Subject "Populationsdynamik"

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Integrated weed management in intensive cropping systems : towards reduction of herbicide input
(2016) Jäck, Ortrud; Gerhards, Roland
Weed control in conventional cropping is commonly done using herbicides. Those, however, can have negative side-effects on the environment. The objective of this thesis is to investigate the potential of reducing herbicide input into cropping systems with a focus on two of the most important staple crops, maize and winter wheat. The thesis is divided into five main sections, dealing with different topics, i.e.: 1. Determination of herbicide efficacy 2. Efficacy of reduced herbicide dosages in maize 3. Efficacy of reduced herbicide dosages in winter wheat 4. Integrated weed management 5. Long-term effect of reduced herbicide dosages To examine herbicide efficacy at reduced dosages it is necessary to conduct a wide range of dose-reponse experiments. They are usually time and labour consuming and the assessment of herbicide efficacy is often not objective. To overcome these issues, a novel method for assessing herbicide efficacy using bi-spectral imaging was tested. The results show at the example of Bromus japonicus that weed coverage assessed with the bi-spectral camera system can serve as a non-destructive, rapid and objective method to assess herbicide efficacy. In field experiments the potential for reducing herbicide dosages in summer maize was investigated with several common herbicides and herbicide mixtures. These experiments show that it is possible to reduce herbicide dosages for weed control in maize without influencing weed control efficacy and crop yield. However, the extent to which dosages can be reduced without loss in efficacy is dependent on the herbicide used and the weed growth stage. One of the herbicide tested in the field (topramezone) is usually applied together with a methylated seed oil (MSO) adjuvant. Adjuvants play an important role for herbicide efficacy, but the mechanism for enhancing herbicide efficacy is often not clear, yet. To examine the mechanism of MSO in enhancing efficacy of topramezone, several experiments were conducted. Efficacy of topramzone was significantly increased by addition of MSO. The results show that MSO enhances the uptake and translocation of topramezone in the two tested weed species. Furthermore, physical properties of the spray solution were altered. More precisely, surface tension and thus the contact angle on the leaf was decreased. These results can explain why MSO adjuvant enhances topramezone efficacy. To investigate the potential of reducing herbicide dosages in winter wheat and its impact on weed seed production, experiments were conducted using A. fatua as weed. The results show, that dosages of the four tested herbicides could be tremendously reduced without loss in efficacy. However, A. fatua seed production was influenced by winter wheat competitiveness and herbicide mode of action and did not necessarily follow herbicide efficacy. These results on the one hand highlight the potential of herbicide dosage reduction for controlling A. fatua in winter wheat. But on the other hand, the results point out that decision on herbicide dosage reduction should not only be made on basis of herbicide efficacy data but also on its influence on weed seed production. Reduction of herbicide input cannot only be achieved by reducing herbicide dosages, but also by applying non-chemical weed control methods. These methods may not be able to fully replace herbicide usage, but they can serve as tool to reduce weed pressure and competitiveness. Field experiments were carried out to investigate the effect of adjusted winter wheat seeding rate and nitrogen fertilization on Calystegia hederacea abundance and herbicide control efficacy. The results show that increased seeding rate reduces density of this weed while enhancing herbicide efficacy. Lowering nitrogen fertilization rate towards Nmin based fertilization increased density of C. hederacea. This study points out how adjustment of agronomic parameters can influence weed competitiveness and can serve in enhancing weed control efficacy by herbicides. It had been shown in several studies that cover crops or undersown crops can effectively suppress weed growth. This suppression may not only be due to competition for resources, but also by chemical interaction via allelopathic active compounds. To examine the allelopathic effect of several cover crops, pot and laboratory experiments were carried out. These experiments show, that effects of the tested cover crops can be growth promoting or inhibiting, and are dependent on the species and extract concentration. Furthermore, cover crops can also affect growth of the crop. To discuss the long-term effect of reduced herbicide dosages on weed population development, a simulation model was set-up at the example of winter wheat and A. fatua. Different strategies for herbicide input reduction were simulated. This paper highlights the potential of reducing total herbicide input without population increase, while keeping grain yield and net return at high level. The presented articles work out the risks and potential for herbicide dosage reduction and point out the possibilities of using integrated weed management options for enhancing weed suppression.
Modeling population dynamics and dispersion of Codling moth Cydia pomonella L. (Lepidoptera, Tortricidae)
(2009) Gharehkhani, Gholamhossein; Zebitz, Claus P. W.
The study of insect dispersal plays an essential role in estimating the spread of damage caused by a newly invaded pest or the spatial distribution of an insect during the active period in growing season. Moreover concerning dispersal, quantitative information performs a crucial role in the evaluation and implementation of pest control. Since rearing clean and healthy insects in sufficient numbers is the most important prerequisite for many basic research programs and for developing pest control strategies, mass rearing of the Codling moth on the artificial diet carried out as the first step at optimum conditions. With regard to the fundamental function of feeding and pre-releasing handling on insect biological attributes, we intended to evaluate the individual marking influence on longevity of Codling moths in the next step. For this purpose, one day old adult male and female moths were kept three and five minutes at -20°C to make them motionless, then immediately marked individually with felt tip pens and coded by the different colors, maintained under optimum condition and checked daily for 13 days. The proposed linear model accounted for 89 % of the variations. Numbing and marking process influenced of the moths longevity regardless of their sex while the duration of the anesthetize does not affect the survival of moths meaningfully. Regarding the obstacles associated with egg and pupa storage of Codling moth, we examined the possibility of adult moth?s storage in low temperature in order to evaluate its eﬀect on longevity of moths. Adult 12-24 h old male and female moths were treated separately and maintained in 4 ◦C and (0:24 h, L:D) photoperiod during the entire adult life. The survival rate evaluated with two days interval throughout 27 days. The effects of day and treatment were significant. It seems that the female moths tolerate the cold condition better and further than the male moths and live longer. Additionally the proposed models accounted for 71 % and 57 % of the variations for male and females respectively as verified more affection and debility of the males by the storage condition. Disadvantages of individual marking led us to test the mass marking and it?s influence on the survival of the moths. One-day-old moths were marked with fluorescent powder. Mortality of the males and females recorded daily for a 20 days period. Results indicated that the effects of the sex, the replications and interaction of them were significant as well as the effect of the day. The model accounted for 96 % of the variations. This study indicated that male and female moths were inﬂuenced by the ﬂuorescent powder. Findings of this study may facilitate the improvement of mark-release experiment results and interpretation more precisely in particular for dispersal studies. In the field experiments, firstly trade off trap structure in assessing the horizontal and vertical distribution of Codling moth carried out as well as outward and inward dispersal. Three different types of the traps including Delta pheromone traps, Delta Pear ester trap and Cylinder shape Pear ester traps were used in the research station of the Hohenheim University. Ninety six traps were suspended in eight compass directions in order of four traps per direction, at three heights in random arrangement in outward dispersal. In inward dispersal study the traps arrangement and number was the same but dissimilarly the releasing site was from borders of directions SW, NW, W, E, and SE. The traps were checked daily and followed nine days after release. Results demonstrated no significant differences between three types of traps in attracting the marked and feral females ?Fn?. Meanwhile significant dissimilarity in marked and feral male ?Mn? catches were traced. Reaction of the moths to the traps elevation was not similar in the vertical distribution study. whereas marked female moths exhibited significant differences to different heights, marked and feral male and ?Fn? moths revealed no difference reaction to traps in different heights.In horizontal distribution study marked female moths ?Fr? exhibited significant differences. It is revealed that dominant directions for marked and feral moths were different. Concerning inward distribution, both marked male ?Mr? and female demonstrated significant differences in their direction and distances. In regard to this findings and priceless and effortless manufacturing of the Cylinder traps, utilization of this trap in mark-release-recapture studies of female and male Codling moths is recommended. Effect of apple cultivar on pheromone and Pear ester trap efficiency studied as the next tread. In this experiment 32 Delta pheromone traps and 32 Cylinder-shape Pear ester traps impartially mounted on different varieties of apple trees. Artificially reared and marked 24 to 26 h old moths were released at 1 m height from a central point. Among the simple effects the most important explanatory variable for the response variables ?Mn? and ?Fn? moths was sampling dates of moths, while the variety and distance from the releasing point for ?Mn? and the variety and trap height for ?Fn? were the second and third influential variables respectively. Moreover among the nested effects the interaction of distance-height-variety was the most influential one for ?Mn? likewise the interactions of date, release point, direction and trap height with the variety were the most influential for ?Fn?. For the ?Mr? and ?Fr? moths releasing date was the most important influential variable, while the trap type and variety for ?Mr? and variety and trap height for the ?Fr? were the second and third influential variables respectively. Current study revealed that dispersal of the feral and marked-released male and female Codling moths influenced by host cultivars distinctly and decidedly. Meanwhile, quantifying these relationships and propose distinct model for marked and feral male and female moths are the exclusive characteristics of present findings. The next stage of present study related to study of climatic factors on dispersal of Codling moth. In this study, Hohenheim station climatic data were used. Several climatic elements including temperature, relative humidity, precipitation, wind speed in two different heights (2.5 m and 10 m), Day Degree, twilight temperature, wind speed and precipitation were utilized in the analysis. Diversity and high number of variables led us to use AIC method for selecting of appropriate regressors and fitted model. The main regressors that inföuenced the ?Fr? were flight height, ageing, twilight wind speed (2.5 m heights) and precipitation. For the ?Mr? the same regressors plus the distance from the releasing point were the best subset. In the case of the feral moths the flight height, relative humidity, Day Degree, twilight temperature and wind speed were the best subset regressors. Comprehensively we concluded that present study provides new knowledge in basic as well as in applied science. Twilight temperature, rainfall, wind speed and Day Degree impress the distribution of the moths in a superior way than the circadian weather data. This knowledge could mitigate confusion which arises from observations of erratic flight patterns and could lead to fewer treatment decision errors in the future. Also may accelerate and strengthen forecasting programs of this key pest as well as the related management tactics. The combination of mark-release-recapture and diffusion models have been shown to be effective for measuring insect dispersal. We attempted to measure the Codling moth dispersal using traps placed at different distances and heights. Diffusion coefficient calculated for horizontal and vertical dispersal of male and female moths distinctly using direct and indirect methods and resulting models were compared. We fitted the non-linear regression using the iterative process and estimating the parameters accuracy were tested according to the default asymptotic 95 % confidence intervals calculation in non-linear regression. Considering the overall models, suitability of three factors fitted models was more convincible than that of two factors model particularly for male moths. Meanwhile we found great difference in the diffusion coeffcient of direct and indirect methods. Regardless of the model type, the R2 was relatively high in our experiments which evaluate how well the model fits data. We have shown that the diffusion model leads to powerful techniques for the analysis of dispersal data at least for one economically important insect. In conclusion, the present study provides an estimate of population spread by Codling moth using estimated rates of reproduction and dispersal, quantified the association between various key factors and Codling moth movement for the first time using the diffusion model. By including additional parameter to the diffusion model the predictive explanatory potential of this method was improved for dispersal studies at least for a cosmopolitan and critical insect.
The host parasite relation of the parasitic mite Varroa destructor (Anderson and Trueman) and the honeybee races A. m. syriaca (Skorikov) and A. m. carnica (Pollmann) in Jordan.
(2006) Al-Attal, Yehya Zaki Khalid; Zebitz, Claus P. W.
Since the honeybee mite Varroa destructor (Anderson and Trueman) succeeded to parasitize the Western honeybee Apis mellifera L. and accept this species as a new host it became the most serious threat to Apiculture worldwide. The very few stable relations between Varroa mites and the new host are either associated with honeybees of African origin, or with tropical and sub-tropical climates. This balanced relations seems to be due to reduced fertility of the female mites in worker brood cells, a shorter post-capping period of the worker brood and a set of highly differentiated active defense traits of the host bees. In this work I investigated several aspects of the host parasite relation between the honeybee and the Varroa mites in Jordan. The endemic honeybee race of Jordan is A. m. syriaca Skorikov, which join African and European bee traits. The Jordanian beekeepers use this ?local? bee as well as its hybrids with imported European bees. Therefore, Jordan provides the possibility to prove the influence of different honeybee races and different climatic conditions on this host-parasite system. For a better direct comparison, I evaluated the host-parasite relation of two honeybee races at the same study site: the ?local? honeybee (A. m. syriaca) and the imported ?carnica? honeybee (A.m. carnica Pollmann), which is susceptible to Varroa infestation under Central Europe conditions.To assess the current status of Varroa mite in Jordan, we surveyed the infestation rates of in capped brood cells and on adult worker bees in 180 honeybee colonies at six locations. All colonies were kept untreated for at least 8 month. The results revealed high infestation rates, which exceed, in part, the thresholds for colony damages. No significant differences between honeybee races or climatic condition were visible. The population dynamics of the host and its parasite represents the most important parameter of the honeybee-Varroa relation and was described in the ?local? and the ?carnica? (imported from Hohenheim) honeybees at Baqa (dry Mediterranean climate) and Yadodeh (wet Mediterranean climate) for a one-year period. In all colonies the number of adult bees and brood cells were evaluated every three weeks by the ?Liebefeld? method. During all evaluations, samples of adult bees and capped brood of all colonies were analyzed to determine Varroa infestation rates. The population dynamics of the honeybee colonies revealed a significantly higher population density of the ?local? honeybee race compared to the ?carnica? colonies. The average number of adult worker bees was 8,368 ± 2,724 in the ?local? colonies and 6,447 ± 2,338 in the ?carnica? colonies, while the average number of capped worker brood cells was 9,164 ± 3,336 in the ?local? and 7,628 ± 3,166 in the ?carnica? colonies. Compared to colonies in Central Europe, my results indicate a surprisingly shorter life span of adult worker bees. The corresponding population dynamics of Varroa mites revealed an exponential growth phase till the maximum infestation and a decreasing phase until the beginning of the next season. The maximum Varroa population density ranged between 2,614 ± 2,190 mites in the ?carnica? colonies and 4,397 ± 2,746 mites in the ?local? colonies. Using an exponential function, growth rate = eb, the average exponential growth rate of Varroa population per three weeks interval ranged between 1.33 and 1.46 and was significantly different between both locations. The subsequent decrease in the mite population was two folds higher than the decrease in the effective bee population (adult bees plus capped worker brood cells together). Therefore, a higher mortality rate of the parasites or its host activity must contribute to the observed drastic decrease of the Varroa population. No significant race-specific differences in the infestation rates could be observed. However, the mortality rate was higher in the ?carnica? colonies (? 40%) compared the local colonies (? 10%). This indicates a general higher fitness of the ?local? colonies independent from Varroa infestation rates. As a threshold for the survival of honeybee colonies, maximum infestation rates of 20% in adult worker bees and 40% in capped worker brood were determined. The evaluated resistance mechanisms, which are considered to contribute to stable host-parasite relations, did not reveal any pre-adaptation of the ?local? honeybee to Varroa mite. Neither in the fertility of female mites nor in the reproductive rate significant differences between the local and the ?carnica? honey bee race could be detected. The post-capping period of the worker brood was nearly the same in both bee races and it corresponds to data from Central Europe. Also no significant difference could be revealed in the daily mite mortality between both races, which ranged between 0.8% and 1.5% of the total mite population in the colonies. Nevertheless, in few individual ?local? colonies, the mite mortality comprises a surprisingly high percentage of the total estimated number of the phoretic mites within the colonies. By RFLP of the CO-I unit, only the V. destructor Korean haplotype was detected in all examined mite samples from Jordan. Additionally, mite genotyping based on the sequences of two genetic markers shows very low genetic variability among different mite populations, which confirm recent publications and makes the hypothesis that differences in mite virulence could be responsible for a stable host parasite relationship, less probable. Conclusions ? The ?local? honeybee of Jordan is not more resistant to Varrosis compared to the susceptible European honeybee races. ? The Mediterranean climate has no significant inhibition effect on Varroa population dynamics. ? Varroa infested ?local? honey bee colonies revealed a significant higher survival rate than imported ?carnica? colonies under the same conditions. ? Variation in the mite infectivity between different V. destructor population is less probable.
Vermehrungs- und Schadpotential der Grünen Gurkenlaus (Aphis gossypii Glover) an Gewächshausgurke (Cucumis sativus L.)
(2003) Bünger, Isa Brigitte Annemarie; Zebitz, Claus P. W.
The aim of this work was to collect basic data for the development of a model which could simulate the injury of greenhouse cucumbers caused by Aphis gossypii G.. This work mainly deals with two aspects: first it is the population dynamics of A. gossypii influenced by infestation density (initial infestation 2-10 individuals per plant) and host plant quality (age) and second it is the quantitative and qualitative assessment of damage by investigation of growth, yield, and chemical composition of the cucumber plants. The investigation took place under controlled, semicontrolld and practical conditions.