Propolis

 
Propolis or bee glue is a resinous mixture that honey bees produce by mixing saliva and beeswax with exudate gathered from tree buds, sap flows, or other botanical sources. It is used as a sealant for unwanted open spaces in the hive. Propolis is used for small gaps (approximately or less), while gaps larger than the bee space (approximately ) are usually filled with burr comb. Its color varies depending on its botanical source, with dark brown as the most common. Propolis is sticky at and above , while at lower temperatures it becomes hard and brittle.
When foraging, worker bees primarily harvest pollen and nectar, while also collecting water and plant resin necessary for the production of propolis. The chemical composition and nature of propolis depend on environmental conditions and harvested resources.
Purpose.
Bees seal the beehive with propolis to protect the colony from the elements, such as rain and cold winter drafts.
Propolis functions may include:
Composition.
The composition of propolis varies from hive to hive, from district to district, and from season to season. Normally, it is dark brown in color, but it can be found in green, red, black, and white hues, depending on the sources of resin found in the particular hive area. Honey bees are opportunists, gathering what they need from available sources, and detailed analyses show that the chemical composition of propolis varies considerably from region to region, along with the vegetation. In northern temperate climates, for example, bees collect resins from trees, such as poplars and conifers (the biological role of resin in trees is to seal wounds and defend against bacteria, fungi, and insects). "Typical" northern temperate propolis has approximately 50 constituents, primarily resins and vegetable balsams (50%), waxes (30%), essential oils (10%), and pollen (5%). Propolis also contains persistent lipophilic acaricides, a natural pesticide that deters mite infestations.
In neotropical regions, in addition to a large variety of trees, bees may also gather resin from flowers in the genera "Clusia" and "Dalechampia", which are the only known plant genera that produce floral resins to attract pollinators. "Clusia" resin contains polyprenylated benzophenones. In some areas of Chile and Argentina Andean valleys, propolis contains viscidone, a terpene from "Baccharis" shrubs, and prenylated acids, such as 4-hydroxy-3,5-diprenyl cinnamic acid. An analysis of propolis from Henan, China found sinapinic acid, isoferulic acid, caffeic acid, and chrysin.
Traditional medicine.
Propolis has been used in traditional medicine, with insufficient evidence to rate its effectiveness in the treatment of any illnesses.
Other uses.
Musical instruments.
Propolis is used by some string instrument makers (violin, viola, cello, and bass) as a varnish ingredient. A tincture of propolis may be used to seal the surface of newly made violin family bridges, and may be used in the maintenance of the bores of pan flute tubes. Propolis was purportedly used by Antonio Stradivari in the varnish of his instruments.