Examining propolis use, social immunity, and food systems transformation to support colony health in honey bees and stingless bees

Abstract

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.