Abstract
Honeybees (Apis mellifera) are threatened by numerous pathogens and parasites. To prevent infections they apply cooperative behavioral defenses, such as allo-grooming and hygiene, or they use antimicrobial plant resin. Resin is a chemically complex and highly variable mixture of many bioactive compounds. Bees collect the sticky material from different plant species and use it for nest construction and protection. Despite its importance for colony health, comparatively little is known about the precise origins and variability in resin spectra collected by honeybees. To identify the botanical resin sources of A. mellifera in Western Europe we chemically compared resin loads of individual foragers and tree resins. We further examined the resin intake of 25 colonies from five different apiaries to assess the effect of location on variation in the spectra of collected resin. Across all colonies and apiaries, seven distinct resin types were categorized according to their color and chemical composition. Matches between bee-collected resin and tree resin indicated that bees used poplar (Populus balsamifera, P. x canadensis), birch (Betula alba), horse chestnut (Aesculus hippocastanum) and coniferous trees (either Picea abies or Pinus sylvestris) as resin sources. Our data reveal that honeybees collect a comparatively broad and variable spectrum of resin sources, thus assuring protection against a variety of antagonists sensitive to different resins and/or compounds. We further unravel distinct preferences for specific resins and resin chemotypes, indicating that honeybees selectively search for bioactive resin compounds.
Highlights
Honeybees (Apis mellifera) are threatened by numerous pests and pathogens [1,2,3]
Our results reveal that bees from our study colonies collected resin from several poplar species (P. balsamifera, P. x canadensis), and from birch (B. alba), horse chestnut (A. hippocastanum) and coniferous trees
While the use of poplar resins had already been confirmed by previous studies [39,45,50], our study provides first evidence for the exploitation of a broader spectrum of resin sources, including poplar species, birch, horse-chestnut and conifers
Summary
Honeybees (Apis mellifera) are threatened by numerous pests and pathogens [1,2,3]. They further have to deal with multiple environmental stressors caused by agricultural intensification, such as pesticides, alteration of foraging landscapes, reduced resource diversity and rapidly spreading new pests and pathogens [4,5,6,7,8,9]. Honeybees perform several collaborative behaviors, such as allo-grooming, nest hygiene or the collection and use of antimicrobial plant resins, which are referred to as social or external immunity and play an essential role for colony health [15,16,17,18]. While much attention has been paid to hygienic behaviors, the use and role of plant resins has been largely neglected until recently [19,20]
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