Benefits of Propolis to Honey Bee Health and Immunity
The goals of this research are to explore ways for beekeepers to encourage honey bee colonies to deposit a propolis envelope within standard beekeeping equipment, and to quantify the benefit of this natural propolis envelope to colony health and immune system functioning, particularly in early spring when colonies in northern climates are subject to molds that commonly grow within the nest after a long winter. If a heavy propolis envelope is a vital component to a healthy bee colony, we can modify the equipment currently used for beekeepers and beekeeping practices nationwide. Such modifications will encourage the bees’ natural construction of a necessary antimicrobial protective envelope in the nest cavity. A long-term outcome of this research is to promote honey bee health, which will directly support local, regional and national beekeepers by having stronger colonies to produce more honey.
Objective 1: Test “propolis trap” configurations to encourage bees to deposit propolis naturally within standard beekeeping equipment. Thirty-six colonies were established in new 10-frame equipment in April 2012. Sister queens were introduced into each colony to reduce genetic variation. Twelve colonies were provided with commercial propolis trap stapled to the four inner walls of each bee box to encourage the bees to build a propolis envelope. This propolis trap is used by commercial beekeepers nationwide and we have confirmed its efficacy in preliminary trials. Another 12 colonies were provided with the propolis traps only on top of the frames, as is done to collect propolis commercially. The last 12 colonies served as controls; no propolis trap was provided and the bees deposited propolis in the cracks and crevices within the box where they could.
Quantify the relative benefit of these propolis configurations to the immune system of individual bees and to viral levels within the colony. Seven day old bees were collected in July 2012, September 2012 and May 2013 to compare the relative immune-gene expression of bees from among the treatments. Candidate genes for immune-related functions, the antimicrobial peptides (AMPs) hymenoptaecin, abaecin and denfensin-2, were selected based on their relevance for the honey bee immune system (Evans et al. 2009). Total RNA was isolated from individual bees using TRIzol (Life Technologies). RNA was reverse transcribed using Superscript II (Invitrogen) and cDNA was quantified through real-time PCR. Colony strength (disease levels, number of adult bees and brood) was also assayed to analyze additional benefits of propolis to colony health and survivorship.
Objective 2: Determine if a propolis envelope can reduce the growth of molds within the nest cavity in early spring, and thus improve colony health. The colonies were overwintered with the propolis traps inside, to determine if the propolis envelope benefits bees during early spring by eliminating molds that develop in the boxes at that time. We did not find mold in the colonies in May of 2013. Therefore, we decided to drop objective 2 from our experiment.
Relative benefit of propolis configurations to the immune system of 7-d old bees: Preliminary findings show that the transcription of all three immune-related genes in bees from colonies with a propolis envelope were lower than in bees from control colonies in both July (F2,395 = 4.5161, P = 0.0115 – hymenoptaecin; F2,364= 45.382, P < 0.001 – abaecin and F2,307= 8.7892, P < 0.001 – defensin-2) and September of 2012 (F2,236 = 8.079, P < 0.001 – hymenoptaecin; F2,335= 4.075, P < 0.001 – abaecin and F2,233= 2.68, P = 0.003 – defensin-2). The difference in the transcription of immune-related genes between colonies with a propolis trap under the inner cover and control was only significantly different for abaecin, for both July (F2,364= 45.382, P < 0.001) and September 2012 (F2,335= 4.075, P < 0.001). These preliminary results suggest that the presence of a natural propolis within the nest acts as an external antimicrobial layer with the propolis envelope being more effective than the propolis trap. As a result, bees from the colonies with a propolis envelope are able to expend less energy during the summer and early fall on immune system function for at least the three immune-related genes studied in this experiment. We believe that the observed decrease in immune-related gene transcription in this study could be due to reduced bacterial loads within the nests of colonies with propolis envelopes. Further work is being conducted to quantitatively determine bacterial levels within the colonies. Gene expression data for May 2013 indicates that the transcription of defensin-2 in bees from colonies with propolis traps are lower when compared to control colonies (F2,157= 5.3092, P = 0.024). However, defensin-2 transcription in bees from the propolis envelope treatment did not differ from either propolis trap or control treatments (F2,157= 5.3092, P = 0.024). Surprisingly, bees of the propolis envelope treatment showed higher transcription of hymenoptaecin (F2,155 = 10.6096, P < 0.002) and abaecin (F2,157 = 1.231, P = 0.051) compared to control colonies. The transcription of hymenoptaecin was also higher in bees from the propolis trap treatment compared to control bees (F2,155 = 10.6096, P < 0.002). The reasons for the greater gene expression for immune-related genes in bees from colonies with either type of propolis treatment are not clear, and several non-mutually exclusive possibilities exist. Additionally, colonies with a propolis envelope that survived the winter had significantly more brood in May 2013 compared to the two other treatments (F2,23 = 5.45, P = 0.01). Another year of data collection will be completed in May of 2014.
Relative benefit of propolis configurations to viral levels within the colony: The relative quantification of honey bee specific virus was assayed by quantitative real-time PCR. Twenty five 7-d old bees per colony were collected and pooled for RNA extraction. One cDNA for each pool was synthesized and a total of 6 cDNAs per treatment were analyzed. Our results indicate that viral loads (Black Queen Cell Virus – BQCV, Deformed Wing Virus – DWV and Israeli Acute Paralysis Virus – IAPV) are not significantly different among treatments. However, this lack of significance might be due to the high variance among pooled samples and the small sample size of our data. Further analysis is being conducted using individual bees in order to decrease variance and increase the sample size of our data.
Impacts and Contributions/Outcomes
Currently, the honey bee population is experiencing a rapid decline in the United States due to the combined effects of diseases, parasites, pesticides and nutritional deficiencies (Cox-Foster et al., 2007; Johnson et al., 2009, 2010; Runckel et al. 2011; Spivak et al., 2011). Since the term Colony Collapse Disorder was coined in 2006 (Skokstad, 2007), national surveys reveal that 30-35% of all honey bee colonies die every winter across the United States (vanEngelsdorp et al., 2007, 2008, 2010, 2011). Beekeepers make up losses by splitting surviving colonies or by purchasing new colonies from national bee breeders and distributors. However, this loss is not sustainable and it is critical that research is undertaken in order to develop methods to improve the natural defenses of honey bees. To our knowledge, this is the first study on the seasonal benefits of propolis for honey bee health and immunity. This research reveals the benefits of propolis to honey bee immune system throughout the year and after the winter, which has a high potential to positively impact bee health, colony strength and consequently, the beekeeping industry. The preliminary results of this research have been presented by R. Borba in nationwide (2013 Entomological Society of America in Austin-TX and 2012 annual North American Pollinator Partneship Conference in Washington-DC) and local meetings (2014 North Central Branch-ESA in Des Moine-IA). M. Spivak has presented on this topic to over 5 different professional and public meetings of beekeepers, scientists and the general public across the US. Beekeeping short-courses offered by the Spivak lab also provide beekeepers easy access to the findings and provide a way to educate beekeepers on sustainable ways to encourage propolis collection. A national survey on bee health has been initiated through the Bee Informed Partnership (www.BeeInformed.org) and beekeepers can evaluate and provide anonymous feedback on the effectiveness of our findings through this website.
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