Browsing by Subject "Honigbiene"

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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”.
Der Einfluss von Wirtsfaktoren der Honigbiene (Apis mellifera L.) auf den Reproduktionserfolg der parasitischen Milbe Varroa destructor (Anderson & Trueman) auf die Auswirkungen einer horizontalen Verbreitung des Parasiten auf den Befall der Bienenvölker
(2014) Frey, Eva; Bessei, Werner
The honey bee colony is faced with a huge number of pathogens, including bee viruses, bacteria, fungi and mites. Among these pathogens, the ectoparasitic mite Varroa destructor is considered the most important parasite of the honey bee worldwide. This mite was discovered at the beginning of the last century in South East Asia within colonies of the original host, the Eastern honey bee Apis cerana. From the middle of the last century the mite has been spread worldwide by transports of infested A. mellifera colonies with dramatic consequences for both, feral and managed honey bee colonies. In the meantime this parasite has become the most serious economic problem for global beekeeping. In temperate climates nearly all honey bee colonies are infested and without yearly Varroa treatments these colonies would collapse within a few years. This confirms that a stable host parasite relationship has not been established yet. Therefore the control of V. destructor still represents the main challenge for beekeeping. The main reason for host damages is the dramatic increase of the Varroa population during the season. Our honey bee colonies are obviously unable to control this population dynamic of the parasite. The increase of the mite population is influenced by the reproductive rate of Varroa females within individual brood cells, by host-parasite-interactions on the colony level and by interactions among honey bee colonies on the population level. The dissertation at hand presents experimental approaches and results at all three levels. On the individual level we were able to demonstrate that age-dependent signals of the honey bee larvae not only activate the oogenesis of the Varroa females but even trigger the further course of mite reproduction. Our studies on the activation of the Varroa reproduction revealed that exclusively larvae within 18 h (worker) and 36 h (drones), respectively, after cell capping were able to stimulate the mite’s oogenesis. Furthermore, we were able to confirm for the first time the presence of a signal in the host larvae allowing the reproducing mites to adjust their own reproductive cycle to the ontogenetic development of the host. Under certain conditions such host signals can even stop an oogenesis of the female mite that has already been started. From an adaptive point of view that sort of a stop signal enables the female mite to save resources for a next reproductive cycle if the own egg development is not sufficiently synchronized with the development of the host. My results indicate that age specific volatiles of the larval cuticle are involved in the regulation of mite reproduction. According to preliminary quantitative GC–MS analysis we suggest certain fatty acid ethyl esters as candidate compounds. These host signals – either involved in the activation or in the interruption of the Varroa reproduction – offer possibilities to influence the reproductive success of Varroa females and might therefore be used for biological control in the future. Within an EU cooperation project we could additionally demonstrate that the so called temporary infertility of Varroa females is significantly correlated with three QTL of the host larvae. This confirms a genetic basis for host resistance factors that inhibit the mite reproduction. For this study we made use of the fact that we had access to a honey bee population at the island of Gotland, Sweden that has survived mite infestation without any treatment for more than 10 years. We crossed a queen from this tolerant population with drones from susceptible colonies to rear hybrid queens and produced a mapping population of haploid drones from these hybrids. Because honey bees have a haplodiploid sex determination, the haploid drones provide an extremely simple and highly efficient model system for genetic studies. Subsequently, we mapped three candidate target regions on chromosomes 4, 7, and 9. Although the individual effect of these three QTL was found to be relatively small, the set of all three had significant impact on the suppression of V. destructor reproduction by epistasis. The detection of this epistatic interaction was only possible because we used the simple genetic make-up of haploid drones. For studies on Varroa resistance on the colony level and for selection programs the interactions among the colonies of the local honey bee population have to be considered. In two experimental approaches I was able to prove that the invasion of Varroa mites from neighboring colonies – often called “reinvasion” – significantly influences the population dynamic of the parasite within the colony. First, we quantified the number of mites invading individual colonies in relation to the invasion pressure (= number and distance of infested colonies). For this approach we made use of an isolated military training area near Münsingen at the Swabian Alb not accessible to other beekeepers. We established ten “mite receiver colonies” continuously treated against V. destructor and placed them at distances of 1m to 1.5 km from four heavily infested “mite donor colonies”. In the donor colonies, we estimated the population of bees, brood, and V. destructor at three week intervals. The invasion of mites into the receiver colonies was recorded every 7-12 days. During the measurement period of about two months, between 85 and 444 mites per colony were introduced into the receiver colonies. Surprisingly, there were no significant differences in the invasion rates in relation to the distance between donor and receiver colonies. The second approach was performed under more realistic field conditions of two experimental apiaries established in regions with high and low bee densities, respectively. Additionally, in this experiment we analyzed the multiplication of the invaded mites. Thereby we confirmed that horizontal transmission plus the reproduction of the invaded Varroa mites can cause an exponential increase of the mite population that may exceed the damage threshold within three months. We were further able to show that the invasion rates – and therefore the final infestation – differ significantly according to the number of honey bee colonies in the neighborhood of the apiary: At the site with a high bee density, the average invasion rate per colony over the entire three and a half months period was 462 mites per colony compared to only 126 mites per colony at the site with a low bee density. As a consequence, the colonies of the apiary at the high bee density site revealed an average final infestation in November of 2,082 mites per colony compared to 340 mites per colony at the low bee density site. The highly infested colonies lost about three times more bees compared to the lower infested colonies – obviously a result of Virus infections transmitted by Varroa mites. With my different approaches I was able to add further elements of knowledge for a better understanding of how host factors and ambient conditions influence the Varroa reproduction within individual brood cells and the population dynamic within a honey bee colony. A better knowledge of these host parasite interactions is essential for the selection of mite resistant colonies and further more important for the development of concepts for an effective Varroa treatment.
Ontogenetic and individual patterns of volatiles in honeybee queens Apis mellifera and its significance for the acceptance of queens in honeybee colonies
(2008) Al Ali Alkattea, Raghdan; Bessei, Werner
Activities of honeybees Apis mellifera L. colony are coordinated by an effective communication network in which the queen plays a central role by controlling behavior and reproduction of workers through pheromones. Most pheromones are produced in the mandibular (QMP) and tergal gland and distributed over the queen?s cuticle. The acquisition of these pheromones from the cuticular body surface of the queen is performed by antennating and licking of the retinue workers. Workers of a colony are able to recognize their own queen. Foreign queens which are introduced without protection are normally killed by the workers. While a lot of work has been performed on the primer and releaser effect of certain queen pheromones, it is still unknown how the workers distinguish their own queen from foreign ones. The fact that queens can be exchanged successfully by protecting the foreign queen for some days demonstrates that workers are able to ?learn? their queen. It is likely that a certain chemical pattern of the cuticle (odor or taste) is finally responsible for the recognition and acceptance as ?own?. In this context, this work has three different objectives: - To better understand the bees? behavior to ?own? and ?foreign? queens and to quantify certain behavioral traits of the queen-workers interaction. - To study the learning ability for own and foreign queens by the use of the Proboscis Extension Reflex (PER) in order to have a tool for future tests of odorous compounds. - To compare the cuticular pattern of queens of different origin. In all three approaches, virgin and mated queens and queens of different kin relation to each other were reared and established in Kirchhainer nuclei colonies. These queens were compared due to the following hypothesis: If the workers perceive their own queen by a distinct smell and if closely related queens have a more similar chemical pattern on the cuticle, then a related foreign queen should be easier ?learned?/ accepted than a non related one. For this purpose, first a specific bioassay had to be developed and established to enable the record of workers behavior to the queen without an inhibition of the complex social interactions between queens and workers. This ?cage bioassay? consists of a small wooden box with a glass front, a wax comb, 30-40 worker bees and a queen. For the tests, the own queen of this mini-colony was removed and a foreign queen was introduced. For a period of about 2 hours certain aggressive and benign actions, respectively, of the workers toward the queen were recorded. In the first set of tests, queens of different kin relations were compared. The results showed, in general, an aggressive reaction against the introduced foreign queens. However, there were clear lower benign and stronger aggression behaviors against unrelated queens compared to the related ones. Some of the unrelated queens were even killed. However, these differences were only significant when virgin queens were exchanged but not when mated queens were used. Concerning the duration of the aggressive action of workers, aggression generally decreased between the beginning and the end of the test; again, this was significant only in the experiments with virgin queens. This indicates, that at least in virgin queens the individual recognition by the worker bees depends on a kin specific odorous pattern of the queen. The same types of queens used in the cage bioassays were used for the learning experiments. A classical olfactory conditioning (PER) of worker honeybees was applied by using a living queen as the source of odor. Hereby the queen was offered in a way that the worker bees could not touch the body surface. The gradual increase in the learning curves was a good indication that the workers are able to learn the queen?s odor and, therefore, can be used as a kind of ?biosensor?. After having learned a queen?s odor, the conditioned workers were tested by offering virgin and mated queens, respectively, with defined kin relation to the queen used for the conditioning before. The results revealed clear differences in the cues used for the ?learning? of individual mated and individual virgin queens, respectively. The workers could significantly discriminate between the learned odor of a mated queen and any other mated queen irrespective of the relatedness. In contrast, worker bees could not discriminate virgin queens from each other. As the worker could only use volatile substances for the associative learning, one can conclude the following: In virgin queens the volatile ?bouquet? is neither individual specific nor kin specific. In mated queens the bouquet has only an individual specificity. Probably, the huge amount of many volatile gland products (including the main component 9-ODA) makes each mated queen ?unique?. But as in the cage bioassays the worker could recognize whether an introduced virgin queen was related to the own queen or not, these recognition must depend on non volatile substances of the virgin queens cuticle which are perceived by licking. If learned and tested queens were of different mating status the worker bees could significantly discriminate between such individuals (except learned odor of mated queens/ tested odor of related virgin queens). This is not surprising because the GC-MS analysis confirmed the huge differences in the odorous pattern (and here mainly the volatile polar gland products) between virgin (= young) and mated (=elder) queens. From the same types of queens used for the cage bioassays and PER, queens? heads and abdomens were extracted in a solvent and the obtained extracts were analyzed using GC-MS. From the extracts of queen abdomens 32 substances (hydrocarbons and polar compounds) were identified and chosen to calculate the ?chemical distance? between queens of different kin relation (sister vs. unrelated) and between sister queens having different ages and mating status. For that purpose, a matrix of Nei-distances was applied as a measure for the similarity of different patterns. The results showed a significantly higher concordance in the chemical pattern within sister queens compared to non related ones. The ?chemical distance? increased from sister queens over half sister to non-related queens. Cluster analyses of the Nei distance and multidimensional scaling clearly confirmed the differentiation between unrelated queens and the similarity of sister queens. Using the same statistical methods, also a clear differentiation between queens of different ages and mating status could be demonstrated. The results presented in this work confirmed with 3 different approaches that workers are able to learn their own queen with different learning cues depending on the mating status of the queen. In virgin queens it could be demonstrated for the first time that the kin relation between different queens can be recognized, presumably by low or non-volatile substances. The chemical analyses confirmed that the cuticular pattern of queens could be used for the differentiation not only according to age but also according to kin.
The production of melezitose in honeydew and its impact on honey bees (Apis mellifera L.)
(2021) Seeburger, Victoria; Hasselmann, Martin
Honeydew honey is a honey type which is of high economic importance in Europe. Phloem sap feeding insects of the order Hemiptera (true bugs) excrete honeydew, the key component of honeydew honey. Beekeepers move their hives between forest regions so that their bees can process the honeydew into honey. In case of high osmolality in the phloem sap of the hemipterans’ host trees, they counteract osmotic pressure by osmoregulation and produce oligosaccharides such as melezitose. Melezitose-rich honeydew honey is a major issue for beekeepers; it crystallises and obstructs the combs, leading to an economical loss. Nevertheless, precise analyses of the conditions of the occurrence of melezitose have not been realised. Furthermore, it is not known which impacts the trisaccharide has on honey bee health and the honeydew flow disease documented in beekeepers’ journals can have one explanation in the nutrition on melezitose. In order to determine influence factors for the emergence of melezitose, more than 600 honeydew droplets from defined honeydew producer species were collected under different environmental conditions (hemipteran species (host tree specific), natural area, air temperature, relative humidity, altitude, time of the year and of the day) between 2016 and 2019. The sugar spectra were analysed by high performance anion exchange chromatography with pulsed amperometric detection. To obtain the impact of melezitose on honey bee health, additional feeding experiments with daily evaluation of food uptake, gut-body weight ratio and mortality have been realised between 2017 and 2019. Additionally, comprehensive 16S rRNA Illumina sequencing of the gut microbial community has been performed. Remarkable differences could be found in the amount of melezitose between honeydew samples collected from different honeydew producer species and according to different environmental conditions. Air temperature increases and decreases in relative humidity increased the melezitose production in honeydew by the observed seven hemipteran species. Both, scale insect species on Picea abies and aphid species on Abies alba produced significantly less honeydew containing melezitose than aphid species on Picea abies. Additionally, honeydew with increased melezitose content was significantly more frequent collected in natural areas with limited water reservoir capacities, at higher altitudes and years with low precipitation. All results lead to the conclusion that hemipteran species produce more melezitose when the host trees have less access to water, increasing the osmolality of the phloem sap and indirectly enhancing the osmoregulation with producing melezitose by hemipteran species. Bees fed with melezitose showed increased food uptake and higher gut-body weight ratio than the control groups. Furthermore, melezitose feeding caused disease symptoms such as swollen abdomen, abdomen tipping and impaired movement and a significantly higher mortality than in control groups. Gut microbiota analyses indicated a shift of the bacterial species Lactobacillus Firm-4 and Lactobacillus kunkeei in favour of Lactobacillus Firm-5 in melezitose fed bees. This PhD project provides the important knowledge about the indicators that point out an enhanced melezitose production. This is a valuable contribution to design a warning system for beekeepers that will help to prevent harmful nutrition for honey bees or crystallised honey in the future by timely removal of bee colonies from local regions at risk. Additionally, feeding experiments point out the high effort that is required for the degradation process of the large-molecule melezitose. This effort might lead to a higher uptake of food, heavier guts, shorter lifespan and a higher susceptibility to intestinal diseases. Finally, an evidence was presented that the lactic acid bacteria of the gut microbiota are significantly involved in the digestion of melezitose.
Theoretical analysis and preference modelling for the valuation of ecosystem services from native pollinators in selected Thai rural communities
(2018) Narjes, Manuel; Lippert, Christian
Until now, the existing microeconomic models concerned with pollination markets have not accommodated the global diversity of beekeeper-farmer interactions. The most prominent of such theoretical models is dedicated to describing the determinants of colony stocking densities and of equilibrium wages that farmers have paid to commercial beekeepers for decades in the highly bee-pollination reliant almond monocultures of California. This cumulative dissertation generalizes this basic model by taking into account the marginal productivity of a given agro-ecosystem’s wild bees and the opportunity costs that farmers incur when assigning labor time to beekeeping. In that regard, we assessed the economic potential of on-farm beekeeping, which can involve several bee species, by juxtaposing this activity’s net benefits against those from hiring commercial pollination services. In addition to serving as a classification tool for a plurality of farmer-beekeeper-nature interactions and related optimization problems, the resulting analytical framework helps identifying the institutional settings that are most likely to lead to a specific bioeconomic equilibrium supply of pollination. What is more, it illustrates the interplay of the pertinent economic and agro-ecological factors, thus assisting the postulation of empirically testable hypotheses. We also conducted two separate discrete choice experiments (DCEs) with orchardists from the Thai provinces of Chiang Mai (N = 198 respondents) and Chanthaburi (N = 127), in order to elicit their preferences for changes in the population of local wild bees that would hypothetically result from a conservation policy consisting (along with a per-household implementation fee) of at least one of the following three measures: (i) offering farmers bee-friendly alternatives to conventional agro-chemicals, (ii) enabling the protection and/or rehabilitation of natural bee habitats near cropland, and (iii) fostering the husbandry of native bee species by transferring technical knowledge on the practice of on-farm beekeeping. In this context, we fitted random parameter logit models on the Chiang Mai dataset. They yielded a significant willingness to pay (WTP) for the presented conservation measures and suggested that the disutility the respondents perceived for a 50% decline in the local population of native bees was greater than the utility they would derive from experiencing a bee population increase of the same magnitude. Moreover, comparing our aggregated WTP estimates to the expected production losses, showed that orchard farmers underestimated the true use value of pollination. On the other hand, the average WTP for all conservation measures combined by far exceeded the costs that, according to our calculations, each household would incur for such a project to be implemented. Our models also indicated a significant preference heterogeneity in the sampled population, which we could partly explain with idiosyncratic variables such as the respondents’ attitudes towards native bees and beekeeping. Finally, we examined further sources of randomness in the observed choice behavior, by modelling the unknown choice decision-relevant influences that could not be captured during the DCEs. To that end, we fitted generalized mixed logit (GMXL) models on the pooled datasets, which allowed comparing, on a common utility scale, the part-worth (value) estimates from Chiang Mai and Chanthaburi, where different experimental designs were applied. Our results reveal that farmers in Chanthaburi, who reported having experienced crop declines that they attributed to insufficient pollination, introduced less subjective factors into their choices than their Chiang Mai counterparts, who may have been less familiar with the importance of conserving bees. Moreover, the GMXL results also suggest that Chanthaburi farmers placed a significantly higher value on the above-mentioned measures (i) and (ii), while caring comparatively less about a 50% decline in local wild bee colonies. One can thus hypothesize that an actual local pollinator decline may have made Chanthaburi farmers more aware of the importance of conserving native bees, while paradoxically making them more independent from the provision of wild pollination services, as they started managing crop pollination with stingless bees.