Comparison of Use and Chemical Composition of Propolis Collected by U.S. Honey Bees
The long-term goal of this research is to investigate the basic biology of resin collection by honey bees. Bees collect resin from trees and shrubs and use it as propolis to seal openings in the nest. This is the first study to document relative propolis use among different lines of bees in the U.S. and the first recent study in the U.S. to identify the plant sources of the resins. It has yielded important baseline information to begin selecting bees for increased propolis use, and basic natural history information on seasonal availability and chemical composition of resins in Minnesota.
Objective 1. Document variability in the amount of resin collection by colonies of four lines of European-derived honey bee subspecies in the U.S.
Objective 2. Characterize the plant source/plant type and analyze the chemical profiles of resins collected by honey bees in MN apiaries.
In the short-term, the results will provide direct feedback to the beekeepers supplying the bees for this research. Additionally, informing beekeepers about the plant sources that honey bees use for resin may help them choose apiary locations for increasing the amount of propolis collected by their colonies.
The long-term goal of this research is to determine the various biological and behavioral components of resin collection by honey bees. Using two sites in Minnesota, this is the first study to document relative propolis use among different lines of bees in the U.S., and the first recent study in the U.S. to identify the plant sources from which honey bees collect resins.
The experiments outlined here will yield important baseline information for future studies including selection of bees for increased propolis use, basic natural history information on seasonal availability, and chemical composition of resins.
The results from this study will be a strong start in investigating this neglected area of honey bee research and will help beekeepers access a secondary income source.
Objective 1: In year 1, 69 colonies were established between two apiaries in Southern MN and monitored every two weeks for level of resin collection. 20 colonies were obtained from a local beekeeper (Honl) who has developed a line of bees from varying racial origin. 20 were Italian honey bees from a CA beekeeper. Another 12 colonies were Italian honey bees from a MN beekeeping operation. The final 17 were Russian honey bees from LA. Two measures of resin collection were used. The first, general measure was total weight of material deposited on a resin trap placed on top of a hive. Then to account for the bees use of wax and resin on the trap, the number of squares filled in on the trap using either resin or wax were also counted.
There were no significant differences between the average resin collected based on location, nor were there overall differences in resin collection across different honey bee lines. However, there was a trend for the Honl colonies collecting more resin than bees from the other lines. Colonies were also separated into high- and low-collecting colonies in order to breed high and low lines for this trait. Colonies selected for high resin collection had traps with significantly more resin deposited on the traps (77.8 ± 58.9 squares resin) than those selected for low resin collection (16.3 ± 19.3), but both types deposited equal amounts of wax on the propolis traps.
In year 2, colonies were again monitored for propolis collection both by trap weight and number of squares filled in with resin or wax. The lines of honey bees used for this portion of the study included Carniolian, Italian, and MN Hygienic honey bees, in addition to the lines that were selected for high and low resin collection. Again, there were no significant overall differences in collection based on location. There were also no significant racial differences. However, the colonies from the line selected for high resin collection did collect significantly more resin (16.7 ± 8.8g resin deposited per month) compared to the low-collecting colonies (2.3 ± 1.6g resin). This was not a result of the low lines using more wax instead of resin in the traps. Additionally, it was confirmed that the number of squares of resin strongly correlated with trap weight (r = 0.81) while amount of wax deposited was weakly correlated (r = 0.33). This indicates that trap weight alone is a good measure of the amount of resin deposited on the traps.
To complete this objective, more analysis will be conducted and a few more samples will be analyzed.
Objective 2: Gas chromatography–mass spectrometry (GC-MS) with electron impact ionization is a common technique to identify the main volatile and semi-volatile components of propolis. I have sampled propolis from 12 of the colonies (3 from each race) in each apiary using GC-MS analysis to determine the chemical profiles of the resins. The samples are currently being analyzed at the University of Minnesota’s Center for Mass Spectrometry and Proteomics. This procedure will not directly identify the species of plant used by each colony but it will allow for the identification of the type of plant source used and determine if there is a difference among colonies with respect to plant type used. Preliminary analyses have shown that the propolis samples are largely characterized by a mixture of flavonoid aglycones, hydroxycinnamic acids and their esters, and likely are derived from poplar species.
I am also currently analyzing seasonal variation in source use. Based on preliminary analyses it appears that some colonies do use some plant sources more than others. It also appears that most colonies rely on only one major plant source throughout a season, but that some colonies shift sources.
This analysis will be completed at the Center for Mass Spectrometry and Proteomics and more samples will be analyzed. It may also be necessary to further analyze samples using HPLC to more accurately identify specific plant sources.
Impacts and Contributions/Outcomes
The current study has yielded important baseline information for future studies involving selecting bees for increased propolis use, and basic natural history information on seasonal availability and chemical composition of resins for two sites in Minnesota. For over a century, beekeepers, particularly in the U.S., have selected lines of bees that deposit less propolis because of its sticky nature. However increasing evidence concerning the medicinal properties of propolis to both humans and bees warrants a reinvestigation into the properties and potential value of propolis collected by honey bees in the U.S. The results will help beekeepers exploit an opportunity for secondary income by selling propolis.
This information has been presented at numerous outlets. M. Simone has presented talks at two MN Hobby Beekeepers Association monthly meetings, MN Honey Producers Association 2007 annual meeting, the American Beekeeping Federation/American Association of Professional Apiculturists 2008 meeting, the 2007 Entomological Society of America annual meeting, the International Union for the Study of Social Insects North American breakout session in 2008, and was an invited speaker at the 2008 meeting of the North Carolina State Beekeepers Association. M. Spivak has presented on this topic to over 25 different professional and public meetings of beekeepers, scientists and the general public in 11 states across the US including 12 talks to groups within MN. She has also presented in Peru, Chile, Argentina, and Nordic-Baltic countries). The Spivak lab has also taught a number of beekeeping short-courses and maintains a web-based course. Through all of these efforts we have created and maintained interest in propolis as both a potential product for sale and as a possible benefit to the health of honey bees.