Resin to Propolis: Biological origins and role in honey bee social immunity and health

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A number of fascinating ecological interactions have evolved between resin producing plants and the wide array of organisms that exploit them. This research will explore how honey bees, Apis mellifera, select and exploit the pharmacological properties of resin to benefit the health of the colony. Honey bees are the most important pollinators of native and agro-ecosystems. Due to the average annual loss of over 30% of the U.S. honey bee colonies since 2006, it is important to promote the natural defenses of honey bees and the economic health of the beekeeping industry. Honey bees collect resin and deposit it in the nest where it is called propolis. A propolis envelope lining the inner walls of the nest acts as an external antimicrobial layer surrounding the colony, benefiting bee immune defenses and colony-level social immunity. This research will explore if plant-derived chemical components in resin provide an important colony defense against both general microorganisms and specific pathogens of honey bees. Further it will determine if bees increase resin collection and/or switch botanical sources of resin to those with greater biological activity after challenge with a bacterial pathogen. Four objectives will be pursued: 1) Determine if the propolis envelope is active against the bacterial pathogen, Paenibacillus larvae, the causative agent of American foulbrood disease in field colonies. Findings will reveal novel approaches to promote honey bee health and explain the function of naturally collected compounds in mitigating diseases of honey bees. 2) Quantify if honey bees increase resin collection in response to challenge with a bacterial pathogen. These studies will shed light on the behavioral mechanisms underlying the collection of resin by a relatively rare subset of bees in the colony whose foraging choices contribute to social immunity at the colony level. 3) Identify the botanical sources of resins used by honey bees for propolis formulation by metabolite fingerprinting analysis. Findings from these analyses will establish the link between the origin of the biologically active substances and their ultimate impacts on honey bee health. This link will provide insight for future studies into the relationship between resin use and health among honey bee subspecies across the globe. 4) Identify bioactive components of propolis that inhibit growth of a honey bee bacterial pathogen using both bioassay-driven purification and metabolomics-based methods. Modern bioassay-guided chemical isolation will facilitate the discovery of previously unknown antimicrobial substances and open new research avenues into the role of resins as pharmacological agents in the ecology and evolution of plant-animal interactions. This research will attract and educate students in disciplines from applied beekeeping to metabolomic analyses and molecular genetics. Through a collaboration with Biology professors at the University of Wisconsin, River Falls, undergraduates participating in the BEE course (Bees Enhancing Education) the will analyze virus levels in bees from propolis-treated colonies, which will help them connect microbiology, ecology, botany, and molecular biology concepts to the relevant, "real-world" problem of pollinator decline. The PI's combined research, teaching, and extension appointments ensure that this research will be translated and disseminated to a diverse audience including scientists, traditional and non-traditional students, beekeepers, and the general public.