Mite that devastates beehives may have been enabled by beekeepers' breeding practices; if so, a fix will take time

A bee infested with varroa destructor mites (IDTools.org)

Beekeepers hate Varroa destructor, the aptly named mite that has infected nearly every beehive in the United States and devastated many of them. But new research published in the Proceedings of the Royal Society suggests that apiarists' own beekeeping practices have unwittingly cleared a path for the mites.

The research focused on propolis, "a sticky material that bees make from a mixture of wax and resins gathered from a wide variety of plants," The Economist reports. "They use it to coat the inner walls of their hives, to plug holes in the hive wall that might otherwise admit predators, and to encase the bodies of those intruders which do manage to breach that wall and have subsequently been stung to death."

Alberto Satta of Sassari University in Italy discovered that hives invaded by Varroa send out more foraging bees to gather plant resins used to make propolis, which contains toxic phenols. He and Francesco Nazzi of Udine University, also in Italy, found that propolis helps protect against mite infestations. They wondered why bees don't use more of it in brood cells, which the mites invade.

"A plausible answer is that the ability to do so has been bred out of them," says The Economist. "Until the revelation of its antimicrobial properties, beekeepers saw propolis as nothing but a nuisance. . . . When hives with removable frames, for the easier collection of honey, were introduced in the mid-19th century, bees retaliated . . . by pasting propolis over those frames, making them hard to extract. To counter this behavior, generations of beekeepers have favored colonies that produced less of the stuff. As a result, modern bees are fairly economical with its manufacture and deployment. Reversing the consequences of such selective breeding will not be easy."

That could involve hybridizing domesticated bees with wild strains of the species, or with other species of bees "that have not lost the knack of making propolis," the Economist speculates. "For that to work, though, would require a concerted effort spread over many places. A more immediate response might be to make it easier for bees to gather the phenol-rich resins which do the mite-killing—perhaps by growing relevant plants near hives. Alternatively, a synthetic version of propolis, introduced into hives by human hand, might then be deployed by the workers in mite-unfriendly ways. Regardless of the exact path out of the mess, though, the sad tale of the honey bee, the propolis and the Varroa mite looks like an object lesson in the law of unintended consequences."