Browsing by Subject "propolis"

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    The effects of propolis on the honey bee (Apis mellifera) immune system and mouthpart microbiome
    (2020-11) Dalenberg, Hollie
    Honey bees (Apis mellifera) collect and apply antimicrobial plant resins to the interior of their nest cavity to form a lining called a propolis envelope. Previous studies show that exposure to a propolis envelope within the nest cavity resulted in reduced immune system activation in adult bees, however the mechanism for this reduction remained unclear. In Chapter 1, I tested the hypothesis that propolis exposure would reduce the general bacterial load (16S rRNA transcription) in and on honey bees, thereby reducing antimicrobial peptide (hymenoptaecin gene) expression by the honey bee innate immune system. The results showed that bees exposed to a propolis envelope in field colonies had significantly lower transcript levels of hymenoptaecin, but in contrast to previous studies had significantly greater 16S rRNA transcription, compared to bees in colonies without a propolis envelope. Bees held in cages had significantly greater hymenoptaecin expression and significantly greater 16S rRNA transcription compared to bees from colonies, suggesting that bees are exposed to different bacterial communities between colonies and cages. The consistent reduction in immune activation yet variable general bacterial loads upon propolis exposure, as seen in previous studies, suggests that there may be a relationship between propolis exposure and the abundance and diversity of specific bacterial species in particular microbial niches in and on the honey bee body. In Chapter 2, I hypothesized that the antimicrobial activity of a propolis envelope in bees from field colonies would influence the bacterial diversity and abundance of the worker mouthpart microbiome. The results of DNA sequencing revealed that the mouthparts of worker bees in colonies with a propolis envelope had significantly lower bacterial diversity and significantly higher bacterial abundance, compared to the mouthparts of bees in colonies without a propolis envelope. Based on the taxonomic results, the propolis envelope appeared to reduce pathogenic or opportunistic bacteria and to promote the proliferation of putatively beneficial bacteria on the honey bee mouthparts, thus reinforcing the core microbiome of the mouthpart niche. This work suggests that the mechanism for reduced immune system activation may be due to the antimicrobial properties of propolis reducing pathogenic and opportunistic bacterial species and promoting beneficial bacterial species in the mouthparts, which may affect disease transmission throughout the colony, thus promoting colony health and wellbeing. This relationships among honey bees, propolis, and microbes likely stems from their long evolutionary history together. The differences in bacterial loads between bees from field colonies and cages suggest that the antimicrobial properties of propolis, the community of microbes, and the individual immune response may vary according to the nest environment, availability of floral resources, and social and organizational behaviors of the bees within the colony.
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    Examining propolis use, social immunity, and food systems transformation to support colony health in honey bees and stingless bees
    (2023-05) Shanahan, Maggie
    As the industrialization of agriculture and other environmental stressors threaten honey bees, stingless bees, and beekeeper livelihoods throughout the world, beekeepers and researchers seek solutions to support bee health. Although many beekeeping practices are designed to support colony health, some inadvertently constrain the natural defenses (or mechanisms of social immunity) that help bees thrive in an unmanaged context. In addition, although most honey bee research seeks to counteract the multiple interacting stressors that cause colony loss, researchers often fail to mention industrial agriculture – the root cause of those stressors – and thus further normalize a major source of bee decline. This dissertation seeks to understand and bolster the natural defenses bees use to support colony health, and to identify ways in which honey bee researchers can reframe their research to contribute to food systems transformation. In Chapter 1, I unpack the relationship between honey bee health and industrial agriculture. I propose steps researchers can take to account for the impacts of this destructive system in our research narratives, and I discuss the uncomfortable questions that surface when we engage in this process. In Chapter 2, I review the use of antimicrobial resin by honey bees and stingless bees for nest construction and defense, and I discuss the ways in which this material contributes, or may contribute, to social immunity in different species. In Chapter 3, I test strategies to stimulate the construction of a robust propolis envelope – a resin-rich structure that wild honey bee colonies build when they nest in hollow tree cavities – in multiple beekeeping contexts. I collaborated with researchers from the United States Department of Agriculture- Agricultural Research Service to assess different surface texture treatments (rough wood boxes, boxes outfitted with propolis traps, and standard, smooth wood boxes) in terms of their ability to stimulate propolis collection, and examined the effect of propolis on colony health, pathogen loads, immune gene expression, bacterial gene expression, survivorship, and honey production. We found that rough wood boxes are the most effective box type for stimulating propolis deposition. The use of rough boxes led to decreased pathogen loads, modulated immune function, and increased colony size. In Chapter 4, I review resin use by stingless bees, specifically. Like honey bees, stingless bees – social, honey-producing bees native to tropical regions – integrate antimicrobial resins in the form of propolis into their colonies. However, the impact of smooth wood box hives on resin collection and the role of propolis in stingless bee colony social immunity have not been examined. In Chapter 5, in collaboration with researchers from the Bee Team at El Colegio de la Frontera Sur, I monitored resin collection and colony development over the course of one year in smooth wood boxes, rough wood boxes modified to mimic hollow tree cavity textures, and thin boxes designed to test the hypothesis that bees use propolis to insulate against temperature change. I also added or removed propolis stores from a second set of colonies and monitored the effect of propolis manipulation on resin foraging and colony development over the course of one year. I found that the use of rough wood boxes leads to increased resin collection, but I did not detect an effect of increased resin collection on colony development. Propolis manipulation in general – and propolis removal specifically – led to increased resin collection, a finding that could have important implications for beekeepers looking to sustainably harvest propolis for medicinal or commercial use.