Honey bees have immune defenses both as individuals and as a colony (e.g., individual and social immunity). One form of honey bee social immunity is the collection of antimicrobial plant resins and the deposition of the resins as a propolis envelope within the nest. In this study, we tested the effects of the propolis envelope as a natural defense against Paenibacillus larvae, the causative agent of American foulbrood (AFB) disease. Using colonies with and without a propolis envelope, we quantified: 1) the antimicrobial activity of larval food fed to 1-2 day old larvae; and 2) clinical signs of AFB. Our results show that the antimicrobial activity of larval food was significantly higher when challenged colonies had a propolis envelope compared to colonies without the envelope. In addition, colonies with a propolis envelope had significantly reduced levels of AFB clinical signs two months following challenge. Our results indicate that the propolis envelope serves as an antimicrobial layer around the colony that helps protect the brood from bacterial pathogen infection, resulting in a lower colony-level infection load.
Bibliographical noteFunding Information:
We would like to thank Gary Reuter and Christine Kulhanek (University of Minnesota) for assistance with honey bee colony management. Dr. Mike Goblirsch (University of Minnesota) and Dr. Jay Evans (USDA-ARS) for valuable discussions. We also acknowledge the support of all the members of the Bee Lab at University of Minnesota. This research was funded by the National Science Foundation IOS 1256992 to M. Spivak.
© 2017 The Author(s).
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