Browsing by Person "Kohl, Patrick L."

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Parasites, depredators, and limited resources as potential drivers of winter mortality of feral honeybee colonies in German forests
(2023) Kohl, Patrick L.; Rutschmann, Benjamin; Sikora, Luis G.; Wimmer, Norbert; Zahner, Volker; D’Alvise, Paul; Hasselmann, Martin; Steffan-Dewenter, Ingolf; Kohl, Patrick L.; Department of Animal Ecology and Tropical Biology, Biocenter, University of Würzburg, Würzburg, Germany; Rutschmann, Benjamin; Department of Animal Ecology and Tropical Biology, Biocenter, University of Würzburg, Würzburg, Germany; Sikora, Luis G.; NaturKonzept, Pfullingen, Germany; Wimmer, Norbert; Bayerische Landesanstalt Für Wald Und Forstwirtschaft, Freising, Germany; Zahner, Volker; Forest Ecology and Management, University of Applied Sciences Weihenstephan-Triesdorf, Freising, Germany; D’Alvise, Paul; Institute for Medical Microbiology and Hygiene, University Hospital Tübingen, Tübingen, Germany; Hasselmann, Martin; Department of Livestock Population Genomics, Institute of Animal Science, University of Hohenheim, Stuttgart, Germany; Steffan-Dewenter, Ingolf; Department of Animal Ecology and Tropical Biology, Biocenter, University of Würzburg, Würzburg, Germany
Wild honeybees ( Apis mellifera ) are considered extinct in most parts of Europe. The likely causes of their decline include increased parasite burden, lack of high-quality nesting sites and associated depredation pressure, and food scarcity. In Germany, feral honeybees still colonize managed forests, but their survival rate is too low to maintain viable populations. Based on colony observations collected during a monitoring study, data on parasite prevalence, experiments on nest depredation, and analyses of land cover maps, we explored whether parasite pressure, depredation or expected landscape-level food availability explain feral colony winter mortality. Considering the colony-level occurrence of 18 microparasites in the previous summer, colonies that died did not have a higher parasite burden than colonies that survived. Camera traps installed at cavity trees revealed that four woodpecker species, great tits, and pine martens act as nest depredators. In a depredator exclusion experiment, the winter survival rate of colonies in cavities with protected entrances was 50% higher than that of colonies with unmanipulated entrances. Landscapes surrounding surviving colonies contained on average 6.4 percentage points more cropland than landscapes surrounding dying colonies, with cropland being known to disproportionately provide forage for bees in our study system. We conclude that the lack of spacious but well-protected nesting cavities and the shortage of food are currently more important than parasites in limiting populations of wild-living honeybees in German forests. Increasing the density and diversity of large tree cavities and promoting bee forage plants in forests will probably promote wild-living honeybees despite parasite pressure.
Reduced parasite burden in feral honeybee colonies
(2023) Kohl, Patrick L.; D'Alvise, Paul; Rutschmann, Benjamin; Roth, Sebastian; Remter, Felix; Steffan‐Dewenter, Ingolf; Hasselmann, Martin
Bee parasites are the main threat to apiculture and since many parasite taxa can spill over from honeybees (Apis mellifera) to other bee species, honeybee disease management is important for pollinator conservation in general. It is unknown whether honeybees that escaped from apiaries (i.e. feral colonies) benefit from natural parasite‐reducing mechanisms like swarming or suffer from high parasite pressure due to the lack of medical treatment. In the latter case, they could function as parasite reservoirs and pose a risk to the health of managed honeybees (spillback) and wild bees (spillover). We compared the occurrence of 18 microparasites among managed (N = 74) and feral (N = 64) honeybee colony samples from four regions in Germany using qPCR. We distinguished five colony types representing differences in colony age and management histories, two variables potentially modulating parasite prevalence. Besides strong regional variation in parasite communities, parasite burden was consistently lower in feral than in managed colonies. The overall number of detected parasite taxa per colony was 15% lower and Trypanosomatidae, chronic bee paralysis virus, and deformed wing viruses A and B were less prevalent and abundant in feral colonies than in managed colonies. Parasite burden was lowest in newly founded feral colonies, intermediate in overwintered feral colonies and managed nucleus colonies, and highest in overwintered managed colonies and hived swarms. Our study confirms the hypothesis that the natural mode of colony reproduction and dispersal by swarming temporally reduces parasite pressure in honeybees. We conclude that feral colonies are unlikely to contribute significantly to the spread of bee diseases. There is no conflict between the conservation of wild‐living honeybees and the management of diseases in apiculture.