Honey bees collect resins on their hind legs from a variety of plants and deposit them in the nest cavity where the resins, often mixed with wax, are called propolis. Two graduate students, Mike Simone-Finstrom (PhD 2010) and Renata Borba (PhD 2015) demonstrated that the presence of a propolis envelope on the inner walls of the nest cavity acts as an antimicrobial layer that enshrouds the colony, providing a quantifiable constitutive benefit to bee immune defenses (Simone et al., 2009; 2017; Borba et al. 2015; 2016). Studies on the microbiota of bees from colonies with or without a propolis envelope revealed that propolis exposure reduced the pathogenic or opportunistic microbes and promoted the proliferation of putatively beneficial microbes that support immune function (Selao et al. 2019; Dalenberg et al. 2020). The propolis envelope also directly reduces the clinical symptoms of two honey bee diseases, chalkbrood and American foulbrood (Simone-Finstrom and Spivak, 2012; Borba and Spivak, 2017). Propolis use by honey bees is an example of social immunity, and is a unique example of social-medication, since bees increase resin collection after challenge with a fungal parasite (Simone-Finstrom and Spivak, 2012).
Based on Mike Wilson’s research (PhD 2013, advised by Dr. Jerry Cohen, Plant Biological Sciences) we are now able to identify the plant source of many honey bee collected resins using metabolomics (Wilson et al., 2013; 2015; 2017). Comparing individual resin loads collected from the hind legs of bees with resin collected directly from a variety of trees, we demonstrated that honey bees collected the majority of their resins in our area from cottonwood trees, Populus deltoides. Resin from P. deltoides has antimicrobial activity against the bacterium Paenibacillus larvae and the fungus Ascosphaera apis, the causative agents of American foulbrood and chalkbrood, respectively. The major antimicrobial compounds in these resins has been identified as a series of novel 3-acyl dihydroflavonols.
Current research, in collaboration with Mike Simone-Finstrom (USDA-ARS Baton Rouge) focuses on developing strategies that beekeepers can use to encourage their bees to construct a healthy propolis envelope, such as testing rough surface textures to stimulate resin collection and using selective breeding to develop bees with propolis-collection genetics (see below).
Current PhD candidate Maggie Shanahan and research technician Héctor Morales Urbina are investigating the importance of propolis to stingless bee, Scaptotrigona mexicana, health in Chiapas, Mexico.
Newest PhD student, Katie Klett, is studying how life-history traits of Apis cerana influence their social immunity. This species of honey bee does not collect propolis, and she will test some hypotheses on physiological mechanisms underlying their unique behaviors that promote colony health.
The publications cited above can be downloaded from here. Research on propolis funded primarily by NSF IOS-0717530 and IOS-1256992, and currently by USDA-NIFA 2018-67013-27532 to M. Spivak.
Honey Bee Hygienic Behavior and Bee Breeding
Our primary and long-term goal is to help honey bees and beekeepers reduce the amount of inputs used in beehives to control diseases and parasitic mites. We have been breeding bees for resistance to these maladies since 1993 with the aim of "getting bees back on their own six feet" to end their reliance on chemical treatments for survival. A reduction in the use of antibiotics and pesticides will reduce operating costs for beekeepers, while ensuring healthy, strong colonies for honey production and pollination, and the purity of honey, wax and other marketable bee products.
Hygienic behavior of honey bees is the main mechanism of resistance to the devastating bacterial disease, American foulbrood, and the fungal disease, chalkbrood. Hygienic bees detect and remove infected brood from the nest before the pathogen becomes infectious. In 1993, we began by breeding a line of honey bees for hygienic behavior with the goal of testing if the behavior is also an effective mechanism of resistance to the parasitic mite, Varroa destructor. Extensive field trials at the University and in collaboration with commercial beekeepers have shown that bees bred for hygienic behavior do detect and remove mite-infested worker brood, and colonies bred for the behavior have reduced mite loads compared to unselected control colonies.
We are no longer maintaining the "MN Hygienic" line of bees, however we continue to encourage beekeepers and bee breeders to select for this and other resistance traits from among their own lines of bees. Read about it: The future of the MN Hygienic stock of bees is in good hands! We have recently initiated a new bee breeding program in which we are selecting for multiple traits: propolis collection, hygienic behavior, low Varroa population growth and virus growth over the season. The hope is to combine all we have learned over the years about social immunity, bee breeding, and beekeeping into one effort.
Research on breeding currently funded by USDA-NIFA 2018-67013-27532 to M. Spivak.