Browsing by Subject "Wechselwirkung"

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    Effects of chronic pesticide and pathogen exposure on honey bee (Apis mellifera L.) health at the colony level
    (2018) Odemer, Richard; Bessei, Werner
    During the last decade the increasing number of honey bee colony losses has become a major concern of beekeepers and scientists worldwide. Extensive research and cooperation projects have been established to unravel this phenomenon. Among parasites, pathogens and environmental factors, the use of agrochemicals, most notably the class of neonicotinoid insecticides, are suspected to be a key factor for this collapse. Current approaches not only focus on colony collapse but also on the weakening of honey bees by the exposure to sublethal concentrations of such pesticides. Recently, the EFSA temporarily banned three neonicotinoids including clothianidin, imidacloprid and thiamethoxam, for the use in crops attractive to pollinators. Thiacloprid however, likewise a neonicotinoid insecticide, is still tolerated for agricultural use because it is considered less toxic to bees. Nevertheless, some publications indicate sublethal effects of this agent leading to impairments of the colony. A general problem for the study of such sublethal effects is that they often are measurable in individual bees without eliciting clear impact at the colony level. In addition, such effects might only have a consequence in combination with other stressors like pathogens. This thesis presents two new methodical approaches combining the controlled application of stressors to individual bees with an evaluation of the effects under field realistic conditions of free flying colonies. In all approaches, the bees were treated with a combination of different pesticides and/or a combination of pesticides and a pathogen in order to evaluate synergistic interactions. As pathogen, Nosema ceranae, a novel intracellular gut parasite introduced from Asia, was used. This parasite is considered to contribute to “CCD”-like symptoms (“colony collapse disorder”), particularly in Spain. In Retschnig et al. (2015), observation hives at two study sites (Hohenheim and Bern) were used to clarify possible synergistic effects when honey bees are exposed to pesticides of two different substance classes (thiacloprid and tau-fluvalinate), both in combination with an infection of N. ceranae. Mortality, flight activity and social behaviour of individually marked and treated worker bees were monitored. At the Hohenheim site, no impact from any of the treatments could be confirmed except a slightly higher flight activity of the Nosema treated bees. At the Bern site however, the pesticide treatments elicited a significant reduction of worker bee lifespan, whereas the Nosema infection resulted in higher ratios of motionless periods. Importantly and in contrast to several laboratory studies, in neither of the two sites an interaction among the pesticides and the pathogen could be confirmed. The inconsistency of our results suggests that the effects of both, sublethal application of pesticides and infection with N. ceranae were rather weak and that interaction among them may have been overemphasized. To extend this first approach in small observation colonies, Odemer & Rosenkranz (2018) focused on performance parameters such as colony development and overwintering in honey bee colonies, using the same pesticides as in the observation hives. Here, neither the single exposure to thiacloprid or tau-fluvalinate nor their combination had negative effects on the colony performance. However, the chronic application of the tau-fluvalinate significantly reduced the infestation with Varroa mites. In Odemer et al. (2018), a neonicotinoid (clothianidin) with an extraordinary high toxicity to bees was applied alone and in combination with N. ceranae and N. apis. A novel approach was developed with individually marked bees that were infected after hatching with a certain number of Nosema spores and introduced into mini-hives. In order to simulate worst case field conditions, the pesticide was then applied chronically in sublethal concentrations over the whole lifespan of the bees. Again in contrast to previous laboratory studies, no effect of the clothianidin treatment on mortality or flight activity could be observed. However, the lifespan of Nosema infected bees was significantly reduced compared to non-infected bees, but in agreement with the observation hive experiment, the combination of pesticide and pathogen did not reveal any synergistic effect. The results of the three experiments of this thesis indicate that (i) individual honey bees are less impaired by neonicotinoids if kept within the social environment of the colony and that (ii) sublethal concentrations of neonicotinoids in the field are not the main driver for colony losses. These statements refer exclusively to the honey bee colony as a eusocial superorganism that obviously is more resilient to pesticide exposure through mechanisms of “social buffering”.
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    Investigations on ruminal degradation of nutrients and feeding values of single feeds and compound feeds for cattle
    (2020) Grubjesic, Goran; Rodehutscord, Markus
    The environmental impact of intensive animal farming has been steadily increasing. Cattle can contribute to environmental pollution due to relatively low nitrogen (N) and phosphorus (P) utilisation, leading to their excess excretion. High-yielding dairy cows are commonly fed concentrate compound feed, in mash or pelleted form, to satisfy high protein and energy requirements. Main source of energy in concentrate compound feeds is starch (ST). For the accurate formulation of compound feeds, comprehensive insight into nutritive values of single feeds as well as their potential interactions (associative effects) when mixed is needed. Typically, the nutritive values of single feeds are considered to be additive, assuming that no associative effects exist. However, data supporting such assumption for concentrate feed are scarce. The present thesis had two aims: evaluation of additivity of ruminal degradation of nutrients and feeding values of single concentrate feeds in compound feeds, and evaluation of effects of pelleting on ruminal degradation of nutrients and feeding values of compound feeds. Twelve single feeds were used to formulate eight compound feeds in different combinations, targeting crude protein (CP) concentrations from 16 to 30% in dry matter (DM). Compound feeds were prepared both, in mash and pellet form in a commercial feed mill using standard industrial conditions. Ruminal degradation of single and compound feeds was evaluated using in situ and different in vitro techniques. The in situ incubations were conducted by incubating samples of all single and compound feeds in polyester bags for 2, 4, 6, 8, 16, 24, 48, and 72 hours in three ruminally fistulated dairy cows. Bag residues were analysed and the ruminal effective degradability (EDIN_SITU) of CP and ST, was calculated for passage rates of 5 and 8%/h. Phosphorus is located in plants as phytate (InsP6), and for some feed samples the EDIN_SITU of InsP6 was also determined. The in vitro gas production (GP), digestibility of organic matter (dOM), metabolisable energy (ME), and utilisable CP at the duodenum (uCP) were evaluated using Hohenheim Gas Test and extended HGT. Intestinal digestibility (IDRUP) of ruminally undegraded protein (RUP) was determined using a three-step enzymatic method through incubation with pepsin and pancreatin. Chemical fractionation of CP was performed according to the Cornell Net Carbohydrate and Protein System (CNCPS) The CP fractions can be also used to predict EDIN_SITU. Assessment of additivity was performed by comparing the observed values of compound feeds with values for compound feeds calculated from single feeds. It was concluded that additivity of single feeds in mash compound feeds was given for EDCPIN_SITU, EDSTIN_SITU (Manuscript 1), uCP, CP fractions, GP, and dOM (Manuscript 2). Here, associative effects among single feeds were considered to be small and should not affect formulation of concentrate compound feeds. The GP and proximate nutrients are necessary to estimate ME using appropriate equations, often specific for feed or feed type. The additivity of ME was given only when same ME equation for single and compound feeds was used. Additivity was not given for IDRUP (Manuscript 2). Pelleting had overall small effects on feeding values of compound feeds determined in situ and in vitro (Manuscripts 1 and 2). Presumably, the relatively low intensity of heating (up to 80–90°C) during the pelleting process was not sufficient to significantly affect nutritive value of compound feeds, with the exception of decreased IDRUP. Overall, it was concluded that additivity of ruminal degradation of nutrients and feeding values of single feeds in mash and pelleted compound feeds can be assumed for practical feed formulation. While some associative effects were detected, they might be related to methodological causes in most of the cases.
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    Sensitivity of land-atmosphere coupling strength in dependence of land cover and atmospheric thermodynamics over Europe
    (2023) Jach, Lisa; Wulfmeyer, Volker
    Biogeophysical feedbacks between the land surface and the atmosphere have been identified to heavily control the climate system. Land-atmosphere (L-A) coupling strength is a concept to quantify the feedback processes. However, the quantification is still subject to uncertainties, in particular, in the context of land surface influences on local convective precipitation. On the one hand, feedback processes are the result of a chain of complex interactions between various components in the L-A system all exhibiting spatiotemporal variability. On the other hand, L-A coupling strength is not a directly measurable quantity. It can be assessed with different scientific approaches, which makes the quantification dependent on the methodology and the availability of suitable data sets. The aim of this doctoral thesis is to investigate the impact of changes in the vegetation cover and the atmospheric thermodynamic conditions on the long-term coupling signal between the land surface and the triggering of deep moist convection during the European summer. The ‘convective triggering potential – low-level humidity index’ framework, which is a commonly used L-A coupling metric, classifies a day in favor for L-A coupling or not, based on the prevailing thermodynamic conditions in the atmosphere. The daily classifications are used to measure the frequency of days with favorable conditions during the study period, and to identify regions with high frequencies of favorable conditions as coupling hot spots. The framework is applied to model output from regional climate model (RCM) simulations with WRF-NoahMP with diverging land cover conducted over the historical period 1986-2015 for the Euro-CORDEX domain. Impacts of changes in vegetation cover are analyzed by comparing the L-A coupling strength from two sensitivity experiments with idealized extreme land use and land cover changes (LULCCs) against a simulation with realistic land cover. A posteriori modifications to the temperature and moisture output fields of the simulation with realistic land cover were implemented to analyze impacts of systematic changes in the atmospheric thermodynamic conditions. A potential coupling hot spot with predominantly positive feedbacks was identified over Eastern Europe. In Southern Europe and Europe’s coastal areas, the coupling is regularly inhibited by very dry, very wet or stable conditions in the atmosphere. The location of the hot spot appeared insensitive to LULCCs and changes in the thermodynamic conditions. None of the sensitivity tests within a realistic range of temperature and moisture modifications for a recent climate period, led to a disappearance of the hot spot or to overcome the causes for inhibiting coupling in the respective areas in summer. Nevertheless, the experiments demonstrated also considerable variance of the coupling strength within the hot spot region. LULCCs changed the turbulent heat fluxes from the land surface, and thus the atmospheric boundary layer (ABL) heating and moistening. This impacted the boundary layer development of each day. It also caused changes in the average thermodynamic characteristics during the study period, which changed the frequency of favorable pre-conditioning for convection triggering and enhanced the variance in the coupling strength in the hot spot. Both effects were identified to influence the land surface control on the occurrence of convective precipitation. Furthermore, the sensitivity tests with a posteriori modifications revealed uncertainties in the predominant atmospheric response to differently wet surfaces around the Black Sea, shown by a disagreement in the predominant coupling pathway between the modification cases. The findings further indicate uncertainty in whether the hot spot expands over Central Europe, as the feedback signal was sensitive to changes in temperature and moisture. Additionally, the model has a warm and dry bias in this area, which suggests an overestimation of the humidity deficit. The large humidity deficit, in turn, was the inhibiting factor for a high frequency of occurrence of favorable pre-conditions for deep moist convection. The analyses reveal a sensitivity of the L-A coupling strength and atmospheric response to the prevailing land surface and atmospheric conditions in the hot spot. This highlights the need to consider both the land surface state and its impact on L-A coupling strength with respect to predictions of convective precipitation events in strongly coupled regions (and periods). Given that L-A coupling provides predictive skill for climate projections and seasonal forecasts, improved understanding about causes of variability in L-A coupling strength is crucial for improvements therein.