Download Benefits of Propolis to Bee Health Final Report Marla Spivak

Benefits of Propolis to Bee Health
Final Report
Marla Spivak
University of Minnesota
[email protected]
We proposed two research objectives: 1) to test if there is a correlation between colony
health and propolis collection in European-derived honey bees, and 2) to compare the immune
systems of African- and European-derived colonies that have been enriched or deprived of a
propolis envelope in the nest cavity.
Objective 1. We placed propolis traps on colonies involved in long-term studies related to
colony health: One set in colonies funded by the USDA- CAP study, and another a USDA study on
the effects of high- and low-agricultural intensity landscapes on honey bee health in North Dakota.
We could not collect data on propolis collection from ND study because the bees chewed up the
mesh traps we (we tried a new type of mesh that clearly didn’t work). We did collect weights of
propolis deposited in the traps in the USDA-CAP colonies, and found a correlation between colony
population (frames of bees in colony) and amount of propolis deposited, but we are waiting for
others in CAP team to finish analyzing colony health data before we can test if there is a correlation
between propolis deposition and colony health. Thus, results are still forthcoming.
Objective 2. We wanted to determine if the heavy propolis envelope in AHB colonies
benefits the immune system as it does in European colonies. In our previous work, we found that
individual bees in propolis-enriched colonies had lower abundance of at least two immune-related
genes (meaning they were not expending energy on a costly immune response), and that this was
likely due to a decrease in bacterial loads in the propolis-rich colonies (Simone et al, 2009,
Evolution). This decreased physiological investment was the first clear evidence that the use of
propolis acts as an external immune defense mechanism for bees.
New graduate student, Renata Borba, from Brazil spent June and July 2011 at the
Universidade de São Paulo in Ribeirão Preto, Brazil, in the labs of Dr. Ademilson Soares and Dra.
Zila Simoes. She set up field colonies of Africanized bees that were made experimentally propolisrich or propolis-poor colonies, using propolis from Minnesota and green propolis from Brazil to
enrich some colonies, and ethanol (the solvent for the propolis) for the control, propolis-poor
colonies. She collected 7d old marked bees and extracted RNA for analysis of transcript levels of 7
antimicrobial peptides.
Her data indicate that bacterial loads in colonies were low in both propolis-rich and poor
AHB colonies. Specifically, the relative gene transcript levels for the general bacterial load (16S
gene) in AHB colonies were the same in 7d old bees from the propolis-treated colonies compared to
same-aged bees from the control colonies. Although was no significant difference was found in
relative transcript levels of the antimicrobial peptide hymenoptaecin, we did a significant difference
in transcript levels of AmEater, a gene involved in cellular immunity. In comparison with our
previously published study, AHB appear to have lower bacterial loads in their colonies relative to
European bees. But like in European colonies, propolis does benefit the immune system of AHB by
decreasing costly investment in at least one antimicrobial peptide. Unfortunately, much of the RNA
degraded in transit between Brazil and MN (the samples were maintained in RNAlater), so we did
not have enough material to test other immune gene transcripts. This preliminary data warrants
repeating on a larger scale, but all analyses will need to be conducted in Brazil to avoid having to
transport the extracted RNA from bees.
How are these findings applicable to beekeeping? We are finding that propolis within a
bee colony is a vital component to bee health and immune system functioning. We are currently
investigating whether the propolis must be a continuous envelope within the inner walls of the
colony, or if it can be placed in a trap on top of the frames, or distributed in patches throughout the
colony. If an envelope is critical, we can easily modify Langstroth boxes so that the lumber inside
the boxes in unfinished, which will stimulate the bees to construct a natural propolis envelope.
Figure 1. Colony of African bees in
Brazil in which side walls of deep
hive body were removed (slat by
slat) to encourage bees to construct
a thick ¼”- ½” wall of propolis. Bees
leave entrance/ventiliation holes in
the propolis envelope. These
colonies comprised resin-rich
colonies, in data below.
Figure 2. Preliminary data on gene
transcript levels of the 16S rRNA loci
were measured as a generic
indicator of the presence of
eubacteria, normalized to the
housekeeping gene actin. Six colony
replicates were done for the two
treatments. Sample size analyzed to
date: control n=5 bees, propolis n= 14
bees. No significant differences
determined by ANOVA (p = 0.75).
Figure 3. Preliminary data on gene
transcript levels for AmEater, a gene
involved in cellular immunity,
normalized to the housekeeping gene
actin. Six colony replicates were done for
the two treatments. Sample size analyzed
to date: control n= 24 bees, propolis n=
32 bees. Significant differences
determined by ANOVA (p = 0.014).
Figure 4. Preliminary data on gene
transcript levels for the immunopeptide
hymenoptaecin normalized to the
housekeeping gene actin. Six colony
replicates were done for the two
treatments. Sample size analyzed to date:
control n= 30 bees, propolis n= 60 bees.
No significant differences determined by
ANOVA (p = 0.38).