Thinking inside the box: restoring the propolis envelope facilitates honey bee social immunity

Authors: SHANAHAN, MAGGIE - University Of Minnesota; Simone-Finstrom, Michael; Tokarz, Philip; Rinkevich, Frank; Read, Quentin; SPIVAK, MARLA - University Of Minnesota

Submitted to: PLOS ONE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/14/2023
Publication Date: 1/31/2024
Citation: Shanahan, M., Simone-Finstrom, M., Tokarz, P.G., Rinkevich Jr, F.D., Read, Q.D., Spivak, M. 2024. Thinking inside the box: restoring the propolis envelope facilitates honey bee social immunity. PLOS ONE. https://doi.org/10.1371/journal.pone.0291744.
DOI: https://doi.org/10.1371/journal.pone.0291744

Interpretive Summary: When wild honey bee (Apis mellifera) colonies nest in hollow tree cavities, they coat rough cavity walls with a thin layer of propolis, derived primarily of plant resins. The resulting “propolis envelope” serves structural and therapeutic functions inside the hive. In this study, we monitored colonies in hive types with different surface texture treatments (rough wood boxes, boxes with propolis traps, and standard, smooth boxes) to determine if these surfaces encourage managed colonies to deposit more propolis. We examined the effect of propolis on colony health, pathogen loads, immune gene expression, bacterial gene expression, and honey production in stationary and migratory beekeeping contexts. Migratory rough box colonies were significantly larger than migratory control colonies by the end of year one. In both stationary and migratory operations, propolis deposition was correlated to a seasonal decrease and/or stabilization in expression of multiple immune and bacterial genes, suggesting that propolis-rich environments help hives maintain consistent environments and reduces the need for bees to increase energetically demanding physiological responses. There was also a significant decrease in European foulbrood gene expression with non-significant decreases in clinical symptoms of this bacterial disease and Varroa loads. These findings provide support for implementation of rough box hives as a means to support propolis collection and colony health in multiple beekeeping contexts.

Technical Abstract: When wild honey bee (Apis mellifera) colonies nest in hollow tree cavities, they coat the rough cavity walls with a thin layer of propolis, a substance comprised primarily of plant resins. The resulting “propolis envelope” serves multiple structural and therapeutic functions inside the hive. Previous studies have shown that the presence of a propolis envelope leads to both individual and colony-level health benefits through the modulation of immune gene expression and the mitigation of pathogen threats. However, the standard wooden bee boxes most commonly used in beekeeping have smooth surfaces that do little to stimulate bees to build a propolis envelope. As a result, although there is growing interest in re-incorporating propolis in the hive environment, propolis has yet to be implemented as a tool to support colony health in commercial beekeeping operations. In this study, we monitored colonies in hive types with different surface texture treatments (rough wood boxes, boxes outfitted with propolis traps, and standard, smooth wood boxes). We evaluated propolis deposition and examined the effect of propolis on colony health, pathogen loads, immune gene expression, bacterial gene expression, survivorship, and honey production in stationary and migratory beekeeping contexts. We found that rough wood boxes are the most effective box type for stimulating propolis collection. Although the use of rough wood boxed did not improve colony survivorship overall, we did observe a significant decrease in Melissococcus plutonius detections via gene expression, and non-significant decreases in clinical symptoms of European foulbrood (EFB) and Varroa mite loads in migratory rough box colonies. By the end of year one, honey bee populations in migratory rough box colonies were also significantly larger than those in migratory control colonies. The use of rough wood boxes did correspond with decreased honey production in year one migratory colonies, but had no effect during year two. Finally, in both stationary and migratory operations, propolis deposition was correlated with a seasonal decrease and/or stabilization in the expression of multiple immune and bacterial genes, suggesting that propolis-rich environments contribute to hive homeostasis. These findings provide support for the practical implementation of rough box hives as a means to enhance propolis collection and colony health in multiple beekeeping contexts.