Browsing by Subject "Insekten"

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Classification and characterization of Ethiopian honey bees (Apis mellifera) based on morphometric, genetic and socio-economic analyses
(2022) Hailu, Teweldemedhn Gebretinsae; Hasselmann, Martin
Ethiopia is a major beekeeping country located in northeast Africa where several evolutionary lineages of Apis mellifera contact. A unique practice of honey bee colony marketing which involves broad agro-ecological zones (AEZs) is a developing trend in the northern part of the country such as Tigray region in association with apicultural development. Several studies based on classical morphometry on the Ethiopian honey bee subspecies classification debated from the unique Apis mellifera simensis to five others. Moreover, the genetic diversity, adaptation, gene flow and inter-relationships of the honey bees between AEZs were not disentangled – a challenge for planning sustainable apicultural development and conservation. Therefore, this study was conducted to elucidate the honey bees of Ethiopia in a context of apicultural transformation using integrated methods: morphometrics, genetics, colony market survey and metadata analyses on beekeeping development. The results of geometric morphometric analyses confirmed that Ethiopian honey bees represented by Apis mellifera simensis references belong to a separate lineage (Y) compared to A, O, M and C, and the present sample belonged to Y. This supported the hypothesis of five major honey bee lineages of the honey bee Apis mellifera. Similarly, a maximum likelihood phylogenetic tree analysis based on the mitochondrial COI-COII showed that most of the Ethiopian honey bees belong to lineage Y. However, a substantial proportion of the samples from the northern part of the country clustered with lineage O, which support the hypothesis that there is close contact between Y and O. Both geometric morphometry and classical morphometry differentiated the Ethiopian honey bees from all references including A. m. monticola, A. m. scutellata, A. m. jementica, A. m. adansonii but grouped with A. m. simensis. Genetically, five DraI haplotypes (COI-COII) were found to be randomly distributed across AEZs, indicating a substantial gene flow. Consequently, the level of genetic differentiation among the Ethiopian honey bee subpopulations defined by local areas and AEZs was generally low based on r7-frag nuclear marker, which is identified to be associated with adaptation to habitat elevation in East African honey bees. Similarly, nucleotide diversity consistently decreased with increasing elevation – indicating a reduced effective population size in the highlands. Results obtained from colony market survey showed that the honey bee swarms are reproduced in a few highlands and re-distributed throughout the region. Colony buyers have preferences of color and AEZ of origin of the honey bees, which led to a one-way flow and eroded the overall level of genetic differentiation. However, a marked differentiation was detected between the highland and lowland honey bees in relic communities where an allelic length polymorphism was observed as a signature of local adaptation. Altogether, Ethiopian honey bees belong to the lineage Y and subspecies A. m. simensis, and are characterized by a high level of gene flow enhanced by colony marketing; but a conserved signature of local adaptation to higher elevations was identified in less disturbed communities. Further studies based on genome-wide analyses and field experiments, focusing on undisturbed communities, can provide more insights into adaptation, admixture and management implications. Sustainable bee breeding and extension services that enable local beekeeping without colony trade and transportation will help to promote apiculture and genetic conservation.
DIY Insektenscheuche : Konzept und Umsetzung im Projekt InsectMow
(2024) Frank, Jonas
Quick guide to building the insect flushing bar from the InsectMow project
Effects of elevated atmospheric CO2 concentrations on insects and pathogens of spring wheat (Triticum aestivum L. cv. Triso) and oilseed rape(Brassica napus cv. Campino)
(2012) Oehme, Viktoriya; Fangmeier, Andreas
It is suggested that plants, herbivore insects and pathogens will be affected by rising atmospheric CO2. The working hypothesis of this study was that elevated CO2 will affect plant composition and will thus exert influence on plant-insect interactions by changing the nutritive value for insects feeding on phloem sap. To test this hypothesis, experiments were carried out on wheat and oilseed rape in two different systems: controlled environment chambers (climate chamber system) and an open field exposure system with natural climatic and soil conditions (Mini FACE system). The abundance of detrimental insects from different feeding guilds and plant damage by parasitic organisms were examined in a Mini FACE system, while the consequences of elevated CO2 on aphid performance and potential correlations to phloem sap composition of host plants were observed in controlled environment chambers. The concentrations of amino acids and carbohydrates in the phloem of host plants were analysed by high?performance liquid chromatography (HPLC), using a fluorescence detector for amino acids and the evaporative light scattering detector for carbohydrates. In a Mini-FACE system, phenological development of spring wheat and OSR was not significantly changed due to CO2 enrichment. However, elevated CO2 induced changes in plant chemistry (increased carbon:nitrogen ratio and defensive compounds), which resulted in changes in population densities of some pest species. In order to monitor alterations in insect population density, two different methods were applied: direct counts (method 1) and using of yellow sticky traps (method 2). These methods showed both increases and decreases of insect numbers due to elevated CO2, depending on species and on the period of observation. Concerning plant pathogens, leaves of spring wheat were only slightly and not significantly damaged by Erysiphe graminis, Puccinia striiformis, Puccinia recondita and Septoria tritici during the 2006/2008 years in all treatments. Also the OSR was not significantly damaged by Peronospora parasitica. The frequency and severity of disease infestation on spring wheat and OSR was not significantly impacted by elevated CO2. In controlled-environment chambers, the phenology, above ground biomass and RGR of OSR were not significantly impacted due to elevated CO2. And although the phenology of spring wheat was not influenced by raised CO2, significant increases were observed for plant above ground biomass and RGR. The aphid presence significantly reduced the aboveground biomass and RGR of spring wheat, while no effects due to aphids were observed in OSR. High-CO2 treatment differently impacted the performance of aphids. Slight and non-significant increases due to elevated atmospheric CO2 conditions were observed for the aphid relative developmental stages and intrinsic rates of increase, while the weight and RGR were significantly increased for Rhopalosiphum padi and decreased for Myzus persicae. In order to clear CO2-impacts on the insect performance, phloem sap from host plants was analysed for the composition and concentration of amino acids and carbohydrates. In summary, although the phenological development of spring wheat and OSR was not affected due to elevated CO2, significant changes were found for the concentration of carbohydrates in the phloem sap of spring wheat and individual amino acids in both host plants. These alterations in plant chemistry affected the performance and abundance of herbivore insects.
Leg attachment and egg adhesion of the codling moth, Cydia pomonella (L.) (Lepidoptera: Tortricidae) to different surfaces.
(2014) Al Bitar, Loris; Zebitz, Claus P. W.
Adults of Cydia pomonella live on host plant surfaces, differing considerably in their structural, chemical, and physicochemical characteristics according to host plant species, cultivar, plant organ, phenological stage, environmental conditions, and orchard management practices. This variable world provided by plant surfaces can profoundly affect many aspects of insect–plant interactions, such as attachment, locomotion, oviposition site selection, egg adhesion, and also survival of adults and their offsprings. Despite their importance, little attention has been given to the structural and wetting properties of the codling moth’s host plant surface and their effect on insect–plant interactions of this important pest. Therefore, studies in this thesis were undertaken to investigate the effect of structural and physicochemical characteristics of the substrate on two main codling moth-plant interactions: (1) the attachment ability of adults, and (2) the adhesion of their eggs. The first part of this thesis was performed to (1) analyze tarsal morphology of male and female C. pomonella to know more about their pretarsal attachment devices, and (2) to investigate their attachment ability on a variety of smooth and rough substrates, using a centrifugal force device. On all smooth artificial substrates tested, both sexes of C. pomonella adults achieved excellent attachment ability, by means of their smooth, flexible and well developed arolia. Hydrophobicity of the substrate had no considerable effect on friction forces. Cydia pomonella females showed a very good attachment ability to the smooth Plexiglas substrate in both horizontal and vertical positions. Thus, it can be concluded that the attachment system of C. pomonella is rather robust against physicochemical properties of the substrate and is able to achieve a very good attachment on vertical and horizontal plant surfaces. Results on the epoxy resin substrates, differing only in surface asperity size ranging from 0-12 µm revealed that the attachment ability of both sexes was significantly affected by surface roughness. Maximal friction force was measured on the smooth substrate whereas minimal friction force was assessed on microrough substrates with 0.3 µm and 1.0 µm size of asperities. On the remaining rough substrates, friction forces were significantly higher but still lower than on the smooth substrate. Both sexes generated similar friction forces on the same substrate, in spite of the considerable difference in their body mass, suggesting that both sexes attach effectively to variable rough plant surfaces in their habitat. However, since smooth surfaces have been reported previously to be the most favorable substrates for ovipositing females of C. pomonella, it is possible that they use their attachment system to sense the substrate texture and prefer those substrates to which their arolia attach the best. A better survival of the codling moth offspring is assumed to be ensured by the selection of suitable oviposition sites by females, as well as by a proper adhesion of deposited eggs to these sites. In apple orchards, eggs of the first generation of the codling moth are laid on leaf surfaces in the vicinity to small fruits, later in the growing season, most eggs are deposited directly on fruits. In the second part of this thesis, egg adhesion of the codling moth to different leaf and fruit surfaces of the domestic apple was investigated by measuring the pull-off force required to detach the eggs from the plant surface. Morphology, wettability, and free surface energy of the tested plant surfaces were analyzed to evaluate their role in egg adhesion. Furthermore, eggs and their adhesives covering leaf or fruit surfaces were visualized. Eggs on the smooth upper leaf sides of the tested cultivars were easily detached, requiring similar pull-off forces (total average of 6.0 mN). Up to 2-3 times stronger pull-off forces had to be applied to detach eggs from the trichome-covered lower leaf side, and these forces differed significantly between cultivars, owing mainly to different trichome covered areas. Whereas on the waxy fruit surface of all apple cultivars tested, eggs were very tightly adhered, and required 4-10 fold stronger pull-off forces than those previously measured on upper and lower leaf surfaces of the identical apple cultivars. Cydia pomonella eggs adhered stronger on the upper and middle fruit sections of all cultivars tested, than on the lower section. The influence of plant surface properties on egg adhesion, as well as the mechanisms used by the moth to overcome the presumable anti-adhesive properties of apple fruit surfaces, were discussed. Additionally, the results were debated in the context of the oviposition site selection, female attachment, as well as offspring survival of the codling moth.
Lokalisation von Pheromon-Rezeptoren und -Bindeproteinen in antennalen Sensillen von Insekten
(2007) Gohl, Thomas; Breer, Heinz
The remarkable reactivity of moth to specific pheromones is based on the extreme selectivity and sensitivity of sensory cells in the male antennae. This feature is supposed to be based on cells equipped with specific receptors. Only the sequencing of the genomes of Bombyx mori and Heliothis virescens provided the possibility to identify candidate genes of olfactory receptors in moths. Upon detailed inspection of candidate receptors it turned out that within the generally very heterogeneous group of receptor-genes a subfamily exists containing members of both species showing striking sequence homology. A conservation of the primary structure of receptors for pheromones has been postulated. For a continuing characterization in these studies different approaches were used to verify that these receptors are indeed expressed in cells of pheromone-sensitive sensilla (sensilla trichodea). By means of ?whole mount? in situ hybridization experiments the RNA of the receptor types BmOR1 and BmOR3 could be visualized in directly neighboring cells reflecting the topology of trichoid sensilla. Also some of the Heliothis receptor types (HR13, HR14, HR16) could be assigned to sensilla trichodea. In addition to the specific receptors, the pheromone binding proteins (PBPs) are expected to play an important role in the detection of hydrophobic pheromone molecules. PBPs are produced by glia-like cells surrounding the sensory neurons. In double in situ hybridization experiments it could be shown that HR13-cells are indeed surrounded by cells expressing HvirPBP1 and HvirPBP2. Analysis comparing the topology of different receptor-types showed that cells expressing HR13 can be assigned to sensilla trichodea type A, whereas HR14 and HR16 are expressed in cells of sensilla trichodea type C. This characteristic expression pattern is considered as a further indication that these candidate-receptors are indeed pheromone-receptors. The assignment of individual receptor-types to distinct sensilla-types provides the basis for investigating the functional implications of receptor-types for the registration of main or minor components of complex pheromone-blends. Further it turned out that HR13 shows coexpression with SNMP1 (sensory neuron membrane protein 1) which is considered as a ?marker?-protein for antennal sensory neurons. This is however not the case for receptor types HR14 and HR16. In search of further SNMP-types screening-experiments were carried out which led to the identification of a novel SNMP-type (SNMP2) of Heliothis virescens. Subsequent studies concerning the expression of SNMP2 showed that the topologic distribution of SNMP2-cells is comparable to SNMP1-cells, but they show a different morphology. Further experiments revealed that SNMP2 is in fact expressed in PBP-producing cells. These findings imply that the proposed putative function of SNMPs has to be reconsidered. One major goal of this study was the attempt, to identify receptor-relevant cells by visualization of mRNA via in situ hybridization but to visualize the localization of the receptor-protein via immunohistochemical approaches. Although the generation of antibodies for olfactory receptors is very difficult, it was possible to raise antibodies specific for receptor type HR13. Using these antibodies in immunohistochemical approaches allowed to also visualize HR13-receptor-protein. By means of double-staining experiments using HR13-specific antisense RNA-probes and anti-HR13 antibodies mRNA and protein were visualized in the same specific cells. Using confocal laserscanning microscopy, it was possible to document that receptor-protein was indeed located in the sensory dendrites. Further, the receptor-protein was also visualized in the axonal processes of sensory cells and the receptor-specific staining revealed that within the antennal nerve HR13-axons appear to be organized in fascicles. These HR13-immunolabeled fascicles were visible until they reach the ?sorting zone? of the antennal lobe; in contrast to mouse olfactory bulb, no receptor specific staining was visible in the antennal lobe.
Sequestration of plant toxins in milkweed bugs (Heteroptera: Lygaeinae) : physiological implications and mechanisms
(2023) Espinosa del Alba, Laura; Petschenka, Georg
Insect herbivores and plants together are a crucial component of terrestrial macro-biodiversity. Within the realm of plant-insect interactions, phytophagy by insects triggered an “arms-race” dynamic resulting in escalatory adaptation and counter-adaptation over time. This coevolution led to complex phenomena such as sequestration of plant toxins by specialized insects, with the main aim to deter predators. Although sequestration is an extensively reported phenomenon, many physiological aspects and underlying mechanisms remain largely unexplored. Milkweed bugs (Heteroptera: Lygaeinae) constitute a versatile model ideally suited for studying both areas due to their particular evolutionary history. They are primarily associated with plant species in the Apocynaceae which commonly produce cardenolides, but remarkably some milkweed bug species secondarily evolved novel associations with phylogenetically disparate plant families supplying new sources of chemically related or unrelated toxins. Using as model milkweed bugs the cardenolide specialist Oncopeltus fasciatus and Spilostethus saxatilis, a species that shifted to sequestration of the chemically unrelated colchicoids, the present thesis first aimed to develop a new artificial diet that allowed the incorporation of the desired types and amounts of toxins without impairing insect performance. Taking a simplified approach, an artificial diet presented in a pill form and made of 100% organic sunflower meal was established. Despite the fact that the new diet has remarkable energy and nutrient differences with sunflower seeds (the laboratory diet), no differences in terms of insect performance were found between the two diets in O. fasciatus and S. saxatilis. Moreover, the new diet presented an acceptable concentration accuracy and shelf-life for short-term toxin feeding assays. Once established, the new diet was used to investigate the effects of cardenolides and colchicoids on several life-history traits of S. saxatilis, and to compare them with the effect of cardenolides in O. fasciatus. Although both classes of toxins have different molecular targets (cardenolides: Na+/K+-ATPase; colchicoids: tubulin), S. saxatilis was able to sequester them at a cost-free level. In fact, an increased performance was observed in O. fasciatus and an according trend was found in S. saxatilis after dietary exposure to cardenolides and colchicoids, respectively. Among cardenolides, labriformin is especially toxic for milkweed-specialist Na+/K+-ATPases in vitro. Nevertheless, it was shown to have no costs in terms of growth and fertility at the whole organism level for O. fasciatus. This finding might be an example of reciprocal evolution between milkweed plants and its herbivores, where highly toxic cardenolides specifically targeted to insect specialists are counteracted by tolerance, detoxification, and sequestration strategies. To assess the role of sequestration beyond normal physiological conditions, O. fasciatus and S. saxatilis were orally infected with the bacterium Pseudomonas entomophila. Neither cardenolides nor colchicoids provided a higher resistance or tolerance. Regarding mechanisms of sequestration, the other overarching research topic of the present thesis, both in vivo (whole animal) and in vitro (isolated digestive tracts) approaches showed no reciprocal competition for the same transport mechanism between chemically related and unrelated toxins. Furthermore, the digestive tract of milkweed bugs did not seem to be a critical mediator as it is for other non-sequestering and sequestering species. The time course of sequestration for the model species was resolved from three days to one hour, and the higher levels of colchicoids detected in S. saxatilis compared to the level of cardenolides in O. fasciatus might indicate an early acquisition of defenses with the shift from cardenolide to colchicoid-containing plants. Finally, a hint to preadaptation mechanisms to resist novel toxins was documented in Spilostethus pandurus, a species that belongs to the same genus as S. saxatilis, thereby providing a basis for future investigations.