Entomology Today By Andrew Porterfield
Propolis, a mass of plant resins built by honey bees inside their hives, has drawn attention in recent years partly because of its alleged (but as yet unproven) health benefits to humans. But, perhaps more important, it also shows health benefits to bees themselves. Created from resins and other oils and fats collected from trees, propolis helps preserve the structural integrity of a bee hive and protects against wood decay, fungus, and water.
Propolis has also been connected to benefiting honey bee (Apis mellifera) immune systems, saving energy that would otherwise have been used to protect against nest-invading beetles like Aethina tumidaor parasites like the Varroa destructor mite, Nosema fungus, and viruses. In the past, some beekeepers have tried to keep their hives “clean” of propolis, believing it impeded with honey-making activities. Today, though, scientists and beekeepers have begun looking at encouraging propolis production to help sustain healthy hives.
In a new study published today in the Journal of Economic Entomology, three researches—Cynthia Hodges, master beekeeper and co-owner of Hodges Honey Apiaries in Dunwoody, Georgia; Keith Delaplane, Ph.D., entomology professor at the University of Georgia; and Berry Brosi, Ph.D., associate professor of environmental science at Emory University in Atlanta—looked at four different ways to enhance propolis growth in bee hives. The team found that three surface modifications—plastic trap material on the hive wall interior, parallel saw cuts on hive wall interior, and brush-roughened wall interiors—were all equally capable of resulting in increased propolis production, compared to a fourth method, a control, in which the hive wall interiors we left unmodified.
The researchers divided 20 colonies into five apiary sites and randomly applied one of the three texture treatments or control to each colony. Bees in the colonies foraged for propolis resins from plants common to the Appalachian Piedmont in the southeastern U.S., including conifers, oaks, pecan, red maple, yellow poplar, and urban ornamental plants. The researchers then measured extensiveness and depth of propolis deposits in the hives over time.
Their results showed that any hive interior treatment significantly increased propolis deposition compared to a non-treatment control. Sampling over time showed propolis hoarding and accumulation, as well. None of the texture treatments showed significantly different results from each other.
While all treatments resulted in more propolis deposition, the researchers point to the roughened interior of the hive walls as the best method for encouraging deposition. In fact, leaving lumber naturally rough, with no planning or sanding, would provide a simple and effective surface for boosting propolis, they write.
“We come down in favor of roughened or un-planed wood,” says Delaplane, “because, unlike the plastic trap, it will not subtract from the bee space engineered around the walls and combs. What you see in our pictures is the work of a steel brush. Naturally un-planed wood would be much rougher and, I would expect, even better at stimulating propolis deposition.”
Other researchers have shown that propolis development has a strong effect on the members of the bee hive. These other investigations have shown that interior walls painted with propolis extract resulted in colonies with lower bacterial loads and with worker bees that expressed lower levels of immune gene expression. Sustained activation of immune genes comes at an energy cost, which can result in a reduction in brood numbers and pose a threat to overall colony health. Further studies have shown that reduced immune activation (and therefore less energy spent on fighting infection) comes from reduced pathogen loads in high-propolis colonies and not from immune suppression by propolis.
“I don’t know of any beekeepers deliberately encouraging their bees to collect propolis,” says Delaplane, adding that many keepers in the past have tried to clear propolis from their hives. “But today we know that this bias is misdirected. I believe encouraging propolis deposition is one more thing beekeepers can do to partner with biology instead of ignore it.”