As Spring completes its transition into Summer our tree bees have removed the propolis that had closed down their entrance for the long Winter. Summer entrances allow for several bees to come and go at once, while in Winter only one or two. This magical sticky substance has long been purported to have curative properties beyond imagination. With marketers promoting propolis for all that ails us...it is ironic to me that we have designed our management practices to discourage the bees from making as much propolis as they would in a tree hollow.
Propolis has been collected for a multitude of uses by humans for centuries. One of the less familiar "Products of the Hive", it has amazing antioxidant properties and like the bees who make it, propolis still holds many sticky secrets. Let’s take some time to wax poetically (poetically propolize?) about propolis.
Propolis – from the Greek "pro" meaning before or in front of and "polis" meaning city. This makes sense as the entrance to the colony is regulated by the bee glue…"before the city". Propolis is as old as honey bees, with records of use by ancient humans from many different cultures.
In cold temperatures (especially when frozen) propolis is brittle and hard. In warmer temperatures it is very sticky but pliable. Propolis can be a consternation to beekeepers because its sticky nature interferes with hive manipulation. Many beekeepers wear bee suits not only to protect from stings but also in an attempt to keep our clothes clean. But propolis has this bright sticky nature that finds a way to stick to and stain where we do not want it. In a wild colony this trait is invaluable.
Bees use propolis to cement and strengthen comb bases, to reduce their entrance in winter, and to embalm dead critters like mice or trap invasive ones (small hive beetle). But in addition to functioning as a construction adhesive, propolis plays important roles in the health of the colony. Colonies in treehollows use propolis to coat the inner walls in what Dr. Thomas Seeley dubbed the "Propolis Envelope", providing a barrier from pests, air flow etc., and hygienically sealing the area.
Langstroth, Warre, Top Bar...all of the popular hive designs have lots of smooth, flat surfaces that the bees leave, while often propolizing the nooks, cracks and crannies. Some beekeepers (myself included) have taken to roughing up those slick surfaces in an attempt to encourage propolization. We're also experimenting with different inner cover materials that the bees might prefer covered in bee glue.
You can see the remains of the propolis coating on the inside of the downed willow branch in the photo below:
Bees make propolis mainly from plant resins and balsams but also add some volatile oils and beeswax. We know tree resin is a part of a tree’s natural defense against insects and fungi and is also produced when a plant is wounded, the antimicrobial properties aiding in the healing process. Bees may prefer some plants with these exudates from buds or bark over others. There may also be specialized dances to send propolis collectors to the best sites.
In Oregon a common provider of the plant material is the balsam poplar and the propolis made from the bud exudates of this tree are highly sought after. The plant material is chewed off the plant and placed by the mandibles onto the forelegs, then they pass this sticky stuff to the inside of the basitarsus of the middle leg that transfers it to the corbicula of the hind leg. Click the photo below for a great article on the thorax.
It is easy to imagine that any number or combination of the natural ways of the honey bee, that we discourage for our own ease, might contribute to a breakdown of their complex social immunities. It's exciting to see some recent studies (see links below) looking into the benefits propolis has on the bee colony. In particular, Dr. Marla Spivak continues to be a champion for this type of practical research. After hundreds of years of selective breeding to minimize propolis production, while looking to capitalize on its benefits for ourselves, the concept deserves our attention. The bees know what they need and often what we do to keep them for our use does not work very well for them. We need to listen to the bees.