THE SCIEN ST
Propolis for Bees
by Marla Spivak & Bridget Mendel Stand near a honey bee hive on a summer day. At
sunlight like sparks; then your eyes hone in on the bees returning from forage. The comers and goers weave through each other seamlessly, bringing back nectar, water, or pollen. You can see the pollen loads, packed on their hind legs like so many colored jewels. But look closer and you might see some bees carrying home another substance: resin. Also transported in the pol- to distinguish from pollen. Pollen comes in seemingly endless shades of color and looks almost velvety in texture. By contrast, resin has a transparent quality.
Ancient beekeepers noted this sticky substance deposited
in large amounts around the entrance of honey bee nests, and named it propolis, which means before the city, surmis- - ers like Aristotle noticed also that the bees gathered it from “tears” of trees. The ancient Greeks and Egyptians knew of its medicinal properties, too, and used it to treat hu- man wounds and infections. Scholars believe the Balm of Gilead mentioned in the bible was actually propolis col- lected from tree buds of the genus Populus, which includes poplar, aspen and cottonwood species. Plant resins are gummy and sticky. A propolis forager bites into the tree resin she’s found, tearing off tiny beads of it from leaf buds or bark, and packing it into her pollen baskets. Once back in the hive, a resin-forag- ing bee can’t easily dislodge the resin from her own legs. Other bees in the nest help remove the resin load bit by bit, by pulling it with their mouth- parts. Bees don’t eat the resin. Instead, they cement it into cracks within the nest cavity, which may be a hollow tree full of crevices, or a manmade bee box.
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The nooks and crannies of a tree cavity stimulate the bees to collect more resin.
- ers have long accepted that propolis serves to waterproof, strengthen, and plug holes within the nest cavity. The nooks and crannies of a tree cavity actually stimulate the bees to collect more resin. Our modern bee boxes, such as the Lang- stroth hives, have smooth-planed sides, so the bees have no crevices to pack with propolis. Instead, they de- posit propolis where it gunks up the movable parts of a modern hive (be- tween frames and hive boxes), making time we beekeepers have discouraged bees from cementing it in the boxes by systematically scraping it away, and by breeding bees that are genetically disinclined to collect much propolis. Because beekeepers in the last de-
cade have struggled to keep their col- onies alive, researchers have turned critical attention to honey bee health. “How can we get bees healthy again?” basically everyone is asking. My team at the U of MN Bee Lab likes to ask,
“How do bees naturally help themselves stay healthy?” One answer, unsurprising perhaps to the average ancient herbalist, is propolis. Now, scientists are scientists because they don’t simply
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