Landesanstalt für Bienenkunde

Permanent URI for this collectionhttps://hohpublica.uni-hohenheim.de/handle/123456789/33

Browse

Now showing 1 - 20 of 44

Bericht der Landesanstalt für Bienenkunde der Universität Hohenheim für das Jahr 2024
(2025) Traynor, Kirsten
Evolutionary genomics of socially polymorphic populations of Pogonomyrmex californicus
(2024) Errbii, Mohammed; Ernst, Ulrich R.; Lajmi, Aparna; Privman, Eyal; Gadau, Jürgen; Schrader, Lukas
Background: Social insects vary considerably in their social organization both between and within species. In the California harvester ant, Pogonomyrmex californicus (Buckley 1867), colonies are commonly founded and headed by a single queen (haplometrosis, primary monogyny). However, in some populations in California (USA), unrelated queens cooperate not only during founding (pleometrosis) but also throughout the life of the colony (primary polygyny). The genetic architecture and evolutionary dynamics of this complex social niche polymorphism (haplometrosis vs pleometrosis) have remained unknown. Results: We provide a first analysis of its genomic basis and evolutionary history using population genomics comparing individuals from a haplometrotic population to those from a pleometrotic population. We discovered a recently evolved (< 200 k years), 8-Mb non-recombining region segregating with the observed social niche polymorphism. This region shares several characteristics with supergenes underlying social polymorphisms in other socially polymorphic ant species. However, we also find remarkable differences from previously described social supergenes. Particularly, four additional genomic regions not in linkage with the supergene show signatures of a selective sweep in the pleometrotic population. Within these regions, we find for example genes crucial for epigenetic regulation via histone modification (chameau) and DNA methylation (Dnmt1). Conclusions: Altogether, our results suggest that social morph in this species is a polygenic trait involving a potential young supergene. Further studies targeting haplo- and pleometrotic individuals from a single population are however required to conclusively resolve whether these genetic differences underlie the alternative social phenotypes or have emerged through genetic drift.
Conserved worker policing in African carpenter ants with drastically different egg chemotypes
(2023) Buellesbach, Jan; Rinke, Janina; Reuter, Leonie; Thomas, Jurian M.; Hartmann, Vivien; Pohl, Marius; Gadau, Jürgen; Ernst, Ulrich R.
Distinctive chemical signatures have the potential to serve as discriminatory cues for olfactory recognition mechanisms. Cuticular hydrocarbon (CHC) profiles are among the most prominent chemical signatures in insects that can be highly diverse even among closely related species and between populations with similar ecology. Particularly within the major insect order Hymenoptera, CHC profiles are characterized by high complexity and variation with the potential to evolve rapidly. In this study, we found two very distinct CHC chemotypes distinguishing sympatric colonies of the African carpenter ant Camponotus maculatus (Hymenoptera: Formicinae). These chemotypic differences were mainly detected on the surface profiles of eggs produced by either queens or isolated worker groups. In one chemotype, queen- and worker-laid eggs are very similar. This is largely contrasted by the other chemotype, where queen-laid eggs clearly differ from worker-laid eggs with several prominent queen-exclusive compounds. However, workers display a stable behavior of discriminating against and selectively disposing of worker-laid eggs i.e., worker policing, independent of egg chemotype. Furthermore, genetic barcoding of workers revealed a clear separation between colonies characterized by producing these two distinct egg chemotypes, which may indicate that these colonies belong to a cryptic species complex. Interestingly, worker policing behaviour appears to be evolutionarily conserved, despite the strikingly different egg surface profiles.
Honey bees (Apis mellifera) preselected for Varroa sensitive hygiene discriminate between live and dead Varroa destructor and inanimate objects
(2023) Sprau, Lina; Traynor, Kirsten; Rosenkranz, Peter
Varroa destructor is one of the main causes of colony losses of the western honey bee ( Apis mellifera ). Many efforts exist to breed honey bees resistant to V. destructor . Varroa sensitive hygiene (VSH) is a commonly selected behavioural trait; VSH workers remove the pupae of mite infested brood cells with high efficiency, interrupting the reproduction of the mite. The cues and triggers for this behaviour are not yet fully understood. To determine what elicits this removal behaviour, we examined preselected VSH workers´ responses to four different groups of objects inserted into freshly capped cells: live mites, dead mites, odour reduced mites, and glass beads. These were also compared to control cells that were opened and closed without inserting any object. The pupae in cells containing inorganic objects (glass beads) were removed at similar rates to the control, demonstrating that an object alone does not trigger a removal response. Dead and odour reduced mites were removed at a higher frequency than control cells, but less frequently than live mites. Workers sometimes removed items resting near the top of the cell without removing the pupa. Our results demonstrate that although mite odour from dead mites triggers removal behaviour, the pupa of cells containing live mites were removed more frequently, suggesting that other cues (i.e. odour from feeding wound) or signals (i.e. pupal movement to signal distress) are important. Future research should focus on elucidating these other cues or signals from the brood and mites, as mite presence alone seems to be insufficient.
Same data, different analysts: variation in effect sizes due to analytical decisions in ecology and evolutionary biology
(2025) Gould, Elliot; Berauer, Bernd J.; Ernst, Ulrich Rainer; Zitomer, Rachel A.
Although variation in effect sizes and predicted values among studies of similar phenomena is inevitable, such variation far exceeds what might be produced by sampling error alone. One possible explanation for variation among results is differences among researchers in the decisions they make regarding statistical analyses. A growing array of studies has explored this analytical variability in different fields and has found substantial variability among results despite analysts having the same data and research question. Many of these studies have been in the social sciences, but one small “many analyst” study found similar variability in ecology. We expanded the scope of this prior work by implementing a large-scale empirical exploration of the variation in effect sizes and model predictions generated by the analytical decisions of different researchers in ecology and evolutionary biology. We used two unpublished datasets, one from evolutionary ecology (blue tit, Cyanistes caeruleus , to compare sibling number and nestling growth) and one from conservation ecology ( Eucalyptus , to compare grass cover and tree seedling recruitment). The project leaders recruited 174 analyst teams, comprising 246 analysts, to investigate the answers to prespecified research questions. Analyses conducted by these teams yielded 141 usable effects (compatible with our meta-analyses and with all necessary information provided) for the blue tit dataset, and 85 usable effects for the Eucalyptus dataset. We found substantial heterogeneity among results for both datasets, although the patterns of variation differed between them. For the blue tit analyses, the average effect was convincingly negative, with less growth for nestlings living with more siblings, but there was near continuous variation in effect size from large negative effects to effects near zero, and even effects crossing the traditional threshold of statistical significance in the opposite direction. In contrast, the average relationship between grass cover and Eucalyptus seedling number was only slightly negative and not convincingly different from zero, and most effects ranged from weakly negative to weakly positive, with about a third of effects crossing the traditional threshold of significance in one direction or the other. However, there were also several striking outliers in the Eucalyptus dataset, with effects far from zero. For both datasets, we found substantial variation in the variable selection and random effects structures among analyses, as well as in the ratings of the analytical methods by peer reviewers, but we found no strong relationship between any of these and deviation from the meta-analytic mean. In other words, analyses with results that were far from the mean were no more or less likely to have dissimilar variable sets, use random effects in their models, or receive poor peer reviews than those analyses that found results that were close to the mean. The existence of substantial variability among analysis outcomes raises important questions about how ecologists and evolutionary biologists should interpret published results, and how they should conduct analyses in the future.
Digest: Better constructing the future than choosing a new habitat
(2022) Ernst, Ulrich R.
What strategy should an individual follow in a heterogeneous environment when its phenotype is not optimized for its current environment: make changes to the environment (habitat construction), move to a different place (habitat choice), or both? Scheiner et al. used an individual‐based model to investigate the interaction of habitat choice and habitat construction. In most situations, habitat construction was superior to either habitat selection or a mixed strategy.
Wirksamkeit, Nebenwirkung und Verteilung von Lithiumchlorid: ein neuer Wirkstoff zur Behandlung von Varroa destructor bei Honigbienenvölkern (Apis mellifera)
(2024) Rein, Carolin Vanessa; Rosenkranz, Peter
Honigbienen sind unverzichtbare Bestäuber sowohl für unser Ökosystem als auch für die Landwirtschaft. Die weltweit verbreitete ektoparasitische Milbe Varroa destructor stellt seit Jahrzehnten das größte Problem für Honigbienen und die Imkerei dar und gilt zweifellos als Hauptverursacher der periodischen Völkerverluste (Genersch et al. 2010; Le Conte et al. 2010). Derzeit gibt es kein zufriedenstellendes Behandlungsverfahren, das alle Anforderungen der Imker erfüllt. Im Jahr 2018 wurde mit Lithiumchlorid (LiCl) ein neuer Wirkstoff mit varroazider Wirkung entdeckt, welcher eine sehr gute Wirksamkeit auf Varroamilben mit einer guten Verträglichkeit für adulte Bienen verbindet (Ziegelmann et al. 2018). Aufgrund der systemischen Wirkungsweise kann er zudem sehr einfach angewendet werden und bietet dadurch großes Potential für eine effektive Varroabehandlung. Im Rahmen der Dissertation wurden verschiedene Applikationsformen von LiCl zur Behandlung von Bienenvölkern getestet und Daten zur Wirksamkeit, Nebenwirkung und Verteilung des Wirkstoffes erhoben. Die gesammelten Daten sollen dazu dienen, eine fundierte Bewertung der Chancen und Risiken für ein Zulassungsverfahren zu ermöglichen und erfolgsversprechende Strategien für die Zulassung zu entwickeln. Zu diesem Zweck wurden verschiedene Feld- und Laborexperimente durchgeführt. Unter praxisnahen Freilandbedingungen führt die Applikation von LiCl zu konzentrationsabhängigen Schäden und hohen Ausräumraten der Bienenbrut. Diese Brutschäden sind von der Dauer der Fütterung und dem Larvenalter abhängig (Rein et al. 2022). Bei einer Fütterung von 25 mM LiCl überleben nur knapp 40% der Bienenbrut. Analysen der Lithium-Konzentration verschiedener Larvenstadien zeigen, dass in zwei Tage alten Larven noch kein Lithium nachgewiesen werden kann. Die Analysen der Futtersaftdrüsen haben bestätigt, dass das Sekret der Ammenbienen, mit dem die Königin und die jungen Larvenstadien gefüttert werden, weitgehend frei von Lithium ist (Rein et al. 2024). Daher sollte eine LiCl-Applikation kein Risiko für die Königin, oder die jungen Larven darstellen. In älteren Larven steigt die Lithium-Konzentration dagegen signifikant an (Rein et al. 2022). Dies ist auf die stadienspezifische Futterumstellung von reinem Futtersaft auf gemischtes Larvenfutter zurückzuführen. Hierbei wird auch eingelagertes Futter aus den umliegenden Waben beigemengt, wodurch auch zuvor eingelagertes Lithium weitergegeben werden kann. Aufgrund der schädigenden Wirkung von LiCl auf die Bienenbrut wurde eine Applikation für brutfreie Völker entwickelt und die Wirksamkeit unter Feldbedingungen getestet. Die Kombination einer brutfreien Phase durch Sperren der Königin mit der LiCl-Behandlung erzielte durchschnittliche Wirkungsgrade von 78 – 98% (Rein et al. 2024). Die höchsten Wirkungsgrade wurden erst bei einer Fütterungsdauer von > 5 Tagen erreicht, was zu Schäden bei der neu angelegten Brut nach der Brutpause führte. In Käfigversuchen, in denen jeweils eine Biene mit einer parasitierenden Milbe mit LiCl gefüttert wurde, konnten dagegen bereits nach 48 Stunden Milbenmortalitäten von über 95% erreicht werden (Rein et al. 2024). Offenbar verzögerte sich im Volk der Wirkungseintritt aufgrund des sozialen Futteraustauschs (Trophallaxis) und einem damit verbundenen Verdünnungseffekt des Wirkstoffs. Jedoch ist dieser Futteraustausch notwendig, um den Wirkstoff gleichmäßig im Volk zu verteilen und alle Milben zu erreichen. Es besteht daher weiterer Optimierungsbedarf, um die für die Zulassung notwendigen Wirkungsgrade von über 90% zu erreichen, ohne die Bienenbrut zu schädigen. Anhand von quantitativen Lithium-Analysen über ICP-OES konnte bestätigt werden, dass der Wirkstoff im Volk gleichmäßig verteilt wird. Bereits einen Tag nach der LiCl-Applikation wurden im Schnitt 93 mg/kg Lithium in den Honigblasen der Bienen nachgewiesen, unabhängig von ihrer Position im Volk (Rein et al. 2024). Analysen der Bienen-Hämolymphe zeigen, dass bereits nach einer 12-stündigen Fütterung der Bienen im Käfig ein Gleichgewicht von 5 – 8 mg/kg Lithium erreicht wird, welches zum Tod der Milbe führt (Rein et al. 2024). Das Lithium sollte daher nach einer LiCl-Applikation möglichst schnell im gesamten Volk verteilt werden und ausreichend lange im Volk zirkulieren, um möglichst in allen Bienen die für Milben tödliche Konzentration zu erreichen. Diese Konzentration sollte für etwa 48 Stunden aufrechterhalten werden, um eine Milbenmortalität von über 95% zu erreichen. Die im Rahmen der vorliegenden Dissertation durchgeführten Versuche bieten eine umfangreiche Basis für die Entwicklung einer zulassungsrelevanten Applikation. Es konnte gezeigt werden, dass Lithium eine hohe akarizide Wirkung besitzt und lediglich noch einige Optimierungen notwendig sind, um eine bessere Verteilung des Wirkstoffes und damit stabile Wirkungsgrade von über 90% bei brutfreien Völkern zu erreichen. Für brütende Völker müssen jedoch alternative Behandlungsmöglichkeiten entwickelt werden, um den Kontakt der Brut mit dem Wirkstoff zu vermeiden.
Temporal increase of Varroa mites in trap frames used for drone brood removal during the honey bee season
(2022) Odemer, Richard; Odemer, Franziska; Liebig, Gerhard; de Craigher, Doris
Varroa mites are highly attracted to drone brood of honey bees (Apis mellifera), as it increases their chance of successful reproduction. Therefore, drone brood removal with trap frames is common practice among beekeepers in Europe and part of sustainable varroa control. However, it is considered labour‐intensive, and there are doubts about the effectiveness of this measure. At present, it is mostly unknown how many mites a drone frame can carry at different times of the season, and how many mites can be removed on average if this measure is performed frequently. Therefore, we sampled a total of 262 drone frames with varying proportion of capped cells (5–100%) from 18 different apiaries. Mites were washed out from brood collected from mid‐April to mid‐July based on a standard method to obtain comparable results. We found that a drone frame carried a median of 71.5 mites, and with the removal of four trap frames, about 286 mites can be removed per colony and season. In addition, mite counts were significantly higher in June and July than in April and May (Tukey‐HSD, P < 0.05). The number of mites and the proportion of capped cells, however, were not correlated (R2 < 0.01, P < 0.05). Our results suggest that drone brood removal is effective in reducing Varroa destructor numbers in colonies, supporting the findings of previous studies on the efficacy of this measure. Although mite counts varied, we believe that increasing sample size over different seasons and locations could elucidate infestation patterns in drone brood and ultimately improve drone brood removal as an integrated pest management tool for a wider audience of beekeepers.
The emergence of ecotypes in a parasitoid wasp: a case of incipient sympatric speciation in Hymenoptera?
(2021) Malec, Pawel; Weber, Justus; Böhmer, Robin; Fiebig, Marc; Meinert, Denise; Rein, Carolin; Reinisch, Ronja; Henrich, Maik; Polyvas, Viktoria; Pollmann, Marie; von Berg, Lea; König, Christian; Steidle, Johannes L. M.
Background: To understand which reproductive barriers initiate speciation is a major question in evolutionary research. Despite their high species numbers and specific biology, there are only few studies on speciation in Hymenoptera. This study aims to identify very early reproductive barriers in a local, sympatric population of Nasonia vitripennis (Walker 1836), a hymenopterous parasitoid of fly pupae. We studied ecological barriers, sexual barriers, and the reduction in F1-female offspring as a postmating barrier, as well as the population structure using microsatellites. Results: We found considerable inbreeding within female strains and a population structure with either three or five subpopulation clusters defined by microsatellites. In addition, there are two ecotypes, one parasitizing fly pupae in bird nests and the other on carrion. The nest ecotype is mainly formed from one of the microsatellite clusters, the two or four remaining microsatellite clusters form the carrion ecotype. There was slight sexual isolation and a reduction in F1-female offspring between inbreeding strains from the same microsatellite clusters and the same ecotypes. Strains from different microsatellite clusters are separated by a reduction in F1-female offspring. Ecotypes are separated only by ecological barriers. Conclusions: This is the first demonstration of very early reproductive barriers within a sympatric population of Hymenoptera. It demonstrates that sexual and premating barriers can precede ecological separation. This indicates the complexity of ecotype formation and highlights the general need for more studies within homogenous populations for the identification of the earliest barriers in the speciation process.
Suitability of sugar, amino acid, and inorganic ion compositions to distinguish fir and spruce honey
(2021) Shaaban, Basel; Seeburger, Victoria; Schroeder, Annette; Lohaus, Gertrud
Honeydew honey is produced by bees from excretions of plant-feeding insects, such as aphids and scale insects. Honeydew on conifers, like fir (Abies alba) or spruce (Picea abies), is produced by different species of the genera Cinara and Physokermes. This means that honeydew honey can stem from different botanical as well as zoological origins, but so far it is not possible to clearly distinguish the different types of honeys. In the attempt to identify distinguishing markers, 19 sugars, 25 amino acids and 9 inorganic ions were quantified in three groups of honeydew honey (fir/Cinara, spruce/Cinara and spruce/Physokermes) with 20 honey samples each. It could be demonstrated that the contents of isomaltose, raffinose, erlose, two undefined oligosaccharides, several amino acids, sulfate, and phosphate differed significantly between the three groups of honey. Furthermore, multivariate analyses resulted in a separation of spruce/Physokermes honey from spruce- or fir/Cinara honey due to its higher contents of phosphate, sulfate, erlose and two undefined oligosaccharides. Moreover, the amino acid composition and the isomaltose as well as the raffinose contents proved useful in the distinction between fir/Cinara and spruce/Cinara honey. In sum, the contents of sugars, amino acids, and inorganic ions in German fir and spruce honeys provide useful information about the botanical and zoological origin of honeydew honeys.
Changes of microorganism composition in fresh and stored bee pollen from Southern Germany
(2021) Friedle, Carolin; D’Alvise, Paul; Schweikert, Karsten; Wallner, Klaus; Hasselmann, Martin
Analysis of plant pollen can provide valuable insights into the existing spectrum of microorganisms in the environment. When harvesting bee-collected pollen as a dietary supplement for human consumption, timely preservation of the freshly collected pollen is fundamental for product quality. Environmental microorganisms contained in freshly collected pollen can lead to spoilage by degradation of pollen components. In this study, freshly collected bee pollen was sampled at different locations and stored under various storage conditions to examine the hypothesis that storage conditions may have an effect on the composition of microorganisms in pollen samples. The samples were analyzed using 16S and 18S amplicon sequencing and characterized by palynological analysis. Interestingly, the bacterial communities between pollen samples from different locations varied only slightly, whereas for fungal community compositions, this effect was substantially increased. Further, we noticed that fungal communities in pollen are particularly sensitive to storage conditions. The fungal genera proportion Cladosporium and Mycosphaerella decreased, while Zygosaccharomyces and Aspergillus increased during storage. Aspergillus and Zygosaccharomyces fractions increased during storage at 30 °C, which could negatively impact the pollen quality if it is used as a dietary supplement.
Pesticide residues in daily bee pollen samples (April–July) from an intensive agricultural region in Southern Germany
(2021) Friedle, Carolin; Wallner, Klaus; Rosenkranz, Peter; Martens, Dieter; Vetter, Walter
Insect-pollinated plants are essential for honey bees to feed their brood. In agricultural landscapes, honey bees and other pollinators are often exposed to pesticides used for cultivation. In order to gain more insight into the fluctuation of pesticide loads, 102 daily pollen samples were collected between April and July 2018 in a fruit-growing area in Southern Germany. Samples were analyzed with respect to more than 260 pesticides using a multi-residue pesticide analysis method. Almost 90% of the analyzed pollen samples featured between one and thirteen different pesticides. In total, 29 pesticides were detected at maximum concentrations of up to 4500 ng/g pollen. Maximum residual concentrations of most pesticides were observed during April and the first half of May, as well as during the second half of June. In most cases, serial data of pesticide residuals were detected for approximately 10 subsequent days with two or three maximum values, which were several folds higher than concentrations on the days before and thereafter. The pollen hazard quotient (PHQ) was calculated to estimate the risk of the detected pesticides to honey bees and wild pollinators.
Comparison of floral traits in Calibrachoa cultivars and assessment of their impacts on attractiveness to flower-visiting insects
(2021) Marquardt, Melanie; Kienbaum, Lydia; Losert, Dominik; Kretschmer, Lea Annina; Rigling, Marina; Zhang, Yanyan; Schweikert, Karsten; Westermann, Nils; Ruttensperger, Ute; Rosenkranz, Peter
Ornamental plants are appreciated by humans for their colorfulness, beauty, abundant flowering and long blooming periods. Many ornamental plants can also constitute an additional foraging resource for flower-visiting insects. However, the ability of the popular ornamental plant Calibrachoa to support urban insect communities is not well documented. In this study, 20 different Calibrachoa cultivars were selected and tested in regard to their insect friendliness based on standardized observations (I) in flight tents using the large earth bumble bee Bombus terrestris as a model species and (II) in open field trials. To investigate what floral characteristics might constitute attractiveness to bumble bees, various floral traits were recorded and compared across all tested Calibrachoa cultivars. Over a two-year period, a total of 6,327 foraging bumble bees were recorded in the tent observations. In the open field observations, we counted 4,188 flower-visiting insects. Our results revealed that (I) all Calibrachoa cultivars were visited by insects for foraging, (II) the number of insect visitors varied significantly among the 20 tested cultivars and (III) the cultivars displayed different floral traits. For the morphometric floral traits and the aroma profiles of Calibrachoa, only the mean nectar quantity and a few identified compounds could be correlated with attractiveness to the model species B. terrestris. We also found that the petal color of the tested cultivars had a significant impact on the number of visitors. Therefore, B. terrestris clearly preferred red or blue Calibrachoa cultivars over those with other petal colors. However, as the cultivar preferences in the different insect groups differed, it is highly recommended to use various cultivars in urban plantings. Nevertheless, efforts must be made to explain what additional floral traits make Calibrachoa and other ornamental plants generally attractive to flower visitors. This information can then be used for breeding purposes to increase the insect friendliness of ornamental plants.
Reproduction of Varroa destructor does not elicit varroa sensitive hygiene (VSH) or recapping behaviour in honey bee colonies (Apis mellifera)
(2021) Sprau, Lina; Hasselmann, Martin; Rosenkranz, Peter
Suppressed mite reproduction (SMR) is an important trait for the selection of Varroa resistant honey bee colonies. It has repeatedly been assumed that SMR is an effect of varroa sensitive hygiene (VSH) when hygienic bees preferably remove those brood cells where the mite has reproduced. We here compare the VSH behaviour of honey bees toward brood cells artificial infested with a varroa mite. By infesting half of the brood cells directly after the cell capping and the other half only 24 h later, we established two groups with high (> 75%) and low (< 2%) mite reproduction. After 8 days, about 40% of the infested brood cells were removed, however without any difference between both groups. Likewise, no group differences were recorded in the percentage of recapped brood cells. This strongly indicates that the presence of mite offspring is not a crucial trigger for the VSH behaviour. SMR data like the percentage of non-reproducing mites are therefore not the optimal measure for the selection of colonies with high VSH.
Evaluation of the importance of ornamental plants for pollinators in urban and suburban areas in Stuttgart, Germany
(2021) Marquardt, Melanie; Kienbaum, Lydia; Kretschmer, Lea Annina; Penell, Anja; Schweikert, Karsten; Ruttensperger, Ute; Rosenkranz, Peter
Urban landscapes are often characterized by a wide range of diverse flowering plants consisting of native and exotic plants. These flower-rich habitats have proven to be particularly valuable for urban pollinating insects. However, the ability of ornamental plants in supporting urban pollinator communities is still not well documented. For this study, we established flower beds at 13 different urban testing sites, which were planted with identical sets of ornamental garden plants. The pollinator visitation patterns were then observed throughout the summer seasons. Over a two-year period, a total of 10,565 pollinators were recorded with wild bees (> 50%, excluding bumblebees) being the most abundant pollinator group. Our results revealed that (I) the assortment of ornamental plants was visited by a high number of urban pollinators for collecting pollen and nectar, and (II) the pollinator abundance and composition varied significantly within the tested ornamental plants. These differences occurred not only among plant species but to the same extent among cultivars, whereby the number of pollinators was positively correlated with number of flowering units per plant. By using a generalized linear mixed model (GLMM) and redundancy analysis (RDA) we identified further significant impacts of the two variables year and location on the insect pollinator abundance and richness. Despite of the local and yearly variations, our approach provided a good and field-applicable method to evaluate the pollinator friendliness in ornamental plants. Such tools are urgently required to validate labels like ‘bee friendly’ or ‘pollinator friendly’ used by plant breeding companies.
Auslöser und Ausprägung des Varroa Sensitiven Hygiene (VSH) Verhaltens im Zusammenhang mit der Reproduktion der Varroamilbe Varroa destructor
(2024) Fölsch, Lina; Hasselmann, Martin
The ectoparasite Varroa destructor causes massive economic damages to the Western honey bee (Apis mellifera) and thus threatens the health of honey bee colonies worldwide. When left untreated, varroa populations can lead to high winter colony losses (Genersch et al. 2010; Traynor et al. 2020; Le Conte et al. 2010). Beekeepers must thus routinely treat against varroa to keep their colonies healthy. A sustainable solution to overcome the varroa problem is selection for varroa resistant honey bees. In addition to studies on natural selection against varroa, there is much interest in breeding varroa resistant honey bees. During varroa resistant selection the focus is often on different selection criteria, such as mite non-reproduction (MNR) and varroa sensitive hygiene (VSH). The selection criteria MNR describes the proportion of non-reproductive mites in a colony (Virag et al. 2022). VSH encompasses the specialized removal behavior of mite infested brood by worker bees (Dietemann et al. 2013; Harbo und Harris 2005). This brood removal interrupts varroa reproduction, which leads to reduced varroa infestation in honey bee colonies. The experiments in thesis were conducted as part of the SETBie project. The SETBie (Selection and Establishment of Varroa-tolerant Bee Colonies) project was a four-year selection project whose objectives included breeding a varroa-resistant honey bee in Baden-Württemberg, Germany. Several institutions and beekeeper organizations cooperated in this project. This dissertation focuses on the factors that trigger VSH behaviour, in addition to documenting the reproductive success of the mite (MNR) in selected colonies. Initial experiments investigated the relationship between VSH and the reproductive success of female Varroa (MNR). A widely held hypothesis was that the reproduction of the mite and the associated nymphal stages in the brood cells triggered the removal behaviour of the workers. However, this hypothesis was disproved by placing mites in capped brood cells and comparing the removal behaviour of reproducing mites with that of mites whose reproduction had been blocked by a special procedure (publication 1). Both groups of mites were removed at a rate of about 40% and did not differ significantly from each other. Therefore, reproduction of the mite could be excluded as a trigger for removal behavior of the workers. This result was supported by simultaneous analysis of VSH behaviour and the proportion of non-reproductive mites (MNR) in a large number of pre-selected colonies. It was also assumed that the increased number of non-reproductive mites (MNR) within a colony is directly connected to VSH behaviour, because the workers would primarily remove the reproductive mites, leaving only non-reproductive mites behind. In addition to providing evidence that mite reproduction is not the trigger of removal behaviour, our analysis of the data collected during the SETBie project showed no correlation between MNR and VSH values (publication 3). The MNR value of a colony therefore does not allow any conclusions to be drawn about the VSH value, which should be taken into account in recommendations for breeding practices. Furthermore, an experiment was conducted to rule out the possibility that removal behaviour effects the normal reproduction of the mite in the next cycle (publication 3). The need for other triggering factors for removal behaviour to occur was clearly demonstrated in this first set of experiments. Varroa mites manipulated to remove specific factors and inanimate objects were placed in capped brood cells to determine what influences removal behaviour. We found that an object (bead) alone does not induce removal behaviour (publication 2). Dead and odour-reduced mites were removed more frequently than the bead and control, but not anywhere near as frequently as live mites. We can thus assume that, in addition to the odour of the mite, the movement of the mite in particular has a signalling effect that triggers this removal behaviour. Other as yet unknown factors such as the reaction of the larvae to the parasitism are likely to play an important role in the removal behaviour of workers. The SETBie project took place over a period of four years, which allowed us to analyse colonies over several generations. Although MNR and VSH are in principle selectable traits, our analysis has shown that they are difficult to improve over multiple generations (publication 4). Colonies with low MNR values could often be improved by crossing them with a drone (artificial insemination) from a colony with a high MNR value. However, it also became clear that it is difficult to maintain high MNR values. Methodological difficulties in targeted selection of MNR/VSH also became noticeable during the collaborative project, which involved the cooperation of numerous breeders. Despite prior infestation of the selected colonies with 180 mites, it was often not possible to collect enough mites to make a valid statement about the reproductive capability of the mite. Even after opening many cells, the minimum number of 10 single infested cells could not be found, which means that MNR values could not be determined for about 63 % of the evaluated colonies due to the presence of too few mites. The selection and breeding work involved in this project is extremely labour-intensive and therefore expensive and requires a high level of expertise among the breeders. It was shown that MNR and VSH are in principle selectable and thus theoretically a Varroa-resistant honey bee line can be bred. However, for future projects, methodological problems need to be resolved or the evaluation methods of the MNR and VSH traits need to be simplified. An optimal solution would be the identification of molecular markers to support selection via genetic heritability. However, this requires further fundamental knowledge about the Varroa mite, the mechanisms that trigger the behaviour of the currently used selection traits, and more precise phenotypic definition of the resistant behaviours.
Bericht der Landesanstalt für Bienenkunde der Universität Hohenheim für das Jahr 2023
(2024) Traynor, Kirsten
Bericht der Landesanstalt für Bienenkunde der Universität Hohenheim für das Jahr 2022
(2023) Traynor, Kirsten
Bericht der Landesanstalt für Bienenkunde der Universität Hohenheim für das Jahr 2021
(2022) Rosenkranz, Peter
Zierpflanzen als Nahrungsquelle und Bewertung der Blütenmerkmale für die Attraktivität der Bestäuberinsekten im urbanen Raum
(2022) Marquardt, Melanie; Rosenkranz, Peter
Currently, an increasing extension of urban areas can be observed worldwide, which implies a concurrent loss in natural habitats. If the current biodiversity shall be preserved, efforts must be reinforced in order to provide alternative habitats for the flora and fauna in urban areas. Regarding the assessment of the ecological value of the habitat ‘city’, scientific studies came to varying conclusions. However, all of them emphasize the importance of green urban areas in promoting the urban biodiversity. It has been frequently pointed out that sufficient and suitable foraging resources are an important and basic requirement for the survival of flower-visiting insects. However, it has hardly been investigated whether ornamental plants are suitable foraging resources for insect pollinators. While this is still highly contentious, there is growing evidence that ornamental plants could contribute to the provision of pollen and nectar. But apparently, the attractivity of different ornamental plants varies widely and furthermore, not all pollinator groups can profit equally from the mostly exotic ornamental plants. At present, scientific data for all ornamental genera or even species are not available. So, the first aim of this study was the comparison of the attractivity of certain ornamental plants, in particular those with a high market value. In order to conduct such trials, already existing acquisition methods have been assessed and refined. A further and so far rarely considered focus of this thesis is the analysis of impact factors that might affect the composition and abundance of urban pollinators. In order to identify the pollinator friendliness of ornamental plants, field tests in urban areas and semi-field tests in flight tents were conducted during the years 2017 – 2019. In the first trail, raised flower beds with an identical set of ornamental plants were installed at 13 different locations in the city area of Stuttgart. During the summer months of the years 2017 and 2018, all flower beds were visited in weekly intervals. Over a time period of 20 minutes, the number of foraging insects – divided into different groups of insect pollinators – was recorded. In total, 10,565 nectar and/or pollen foraging insects were counted. First of all, this confirms that our selection of ornamental plants was used as a foraging resource by pollinating insects. The attractivity of the tested ornamental plants, however, varied to a considerable degree among the plant species and the number of counts ranged from 1.2 flower visits in 20 minutes on Bracteantha bracteata (strawflower) to 5.3 flower visits on Bidens (beggar-ticks). It is noteworthy, that the attractivity also varied within the cultivars of the same species, partly even to a greater extent than between species. Interestingly, not only the abundance but also the composition of pollinators varied among the different test plants. Furthermore, the applied statistical models indicate significant impacts of the study year and the location on the results. This highlights the need of a continuously testing of all ornamental plants in regard to insect friendliness, for which the described methods were found to be very appropriate (publication I). Pollinating insects often use characteristic floral traits of the plants for their decision to visit the respective flower. These floral traits are often genera-, species- or even cultivar-specific and have been well studied in the native plants. In contrast, very little is known about the role of floral traits in ornamental plants. This includes e. g. the petal colour, several floral morphomet-rics or the floral scent of different plants. The impact of these traits on attractivity for insects was analysed in semi-field experiments using Calibrachoa cultivars and Bombus terrestris as model pollinator. Similar to the first part of the thesis, the attractivity of the different cultivars varied significantly. While the floral scent explained the observed differences in attractivity only to a small extend, it could be shown unequivocally that the petal colour constitutes a significant factor in the attractivity on B. terrestris. For a better understanding on the impact of certain floral traits for pollinating insects, however, there is further research required (publication II).

Browse

Recent Submissions