Going after “enemy no.1” for honey bees

The U of MÂ’s Bee Lab is raising awareness about varroa mites, a deadly pest for honey bees

Becky Masterman of the University of Minnesota Bee Squad prepared to gather honey bees to check for varroa mites. Credit: Dylan Thomas

DOWNTOWN WEST — The University of Minnesota’s Bee Squad aims to raise awareness this fall about a tiny parasite that is one of the biggest threats to Minnesota honey bee colonies.

Varroa mites are “enemy no. 1” for honey bees, said Bee Squad Associate Program Director Becky Masterman, who on Monday used the two beehives atop Minneapolis City Hall to demonstrate a fast and easy way to test for an infestation. Both beehives showed signs of a “heavy infestation” that could spread to nearby hives, Masterman said.

She’ll return later in the week when cooler weather will allow her to treat the infestation with oxalic acid, a method common in Canada and Europe but only recently approved by the U.S. Environmental Protection Agency. Her goal is to encourage Minneapolis’ dozens of backyard beekeepers to take the same steps over the next few weeks.

Masterman described varroa mites as “a major cause of bee death,” but they’re just one in a complex of factors that is contributing to widespread honey bee losses, a phenomenon often referred to as Colony Collapse Disorder. Poor nutrition, exposure to pesticides, diseases and pests like the varroa mite are all contributing to colony die-offs.

“In Minnesota, we have some of the highest winter losses and summer losses in the country,” Masterman said.

Surveys have shown about one-third of honey bees in managed colonies dying across the U.S. annually since 2006. Recently in Minnesota, it’s been closer to 50 percent, Masterman said.

As awareness of honey bee health and the crucial role of insect pollinators has spread, so too has interest in keeping hives. An ordinance allowing for backyard beekeeping passed in Minneapolis in 2009. Beehives were placed atop Minneapolis City Hall in 2013.

Minneapolis Sustainability Director Gayle Prest said the city plans to survey backyard beekeepers this winter to get a clearer picture of the number of hives and their locations. Backyard beekeepers are only required to get a permit once, in their first year, and many don’t keep up with what can be a demanding hobby.

Prest said over 80 permits for beehives were pulled this spring, one measure of the activity’s popularity. Masterman said the Bee Squad’s class for beginner beekeepers enrolled 750 people this year.

Good hive management is crucial, in part because health issues like a varroa mite infestation can spread from hive to hive. Bees range up to three miles when searching for food sources in an urban environment. Mite infestations spread when bees rob honey from nearby hives or through “drone drift,” which is when male bees fly off and join a different colony, Masterman explained.

After opening the wooden beehives on City Hall’s grass-covered green roof, Masterman collected several hundred bees in a small glass jar. She then dusted the insects with powdered sugar, explaining that the small amount of cornstarch in the sugar would help the bees rub off the mites. Masterman then turned the jar over and shook it, and dozens of tiny mites fell like black pepper through holes in the jar’s lid.

It was too warm Monday to apply the oxalic acid, but later in the week Masterman plans to drizzle a solution of the acid mixed with simple sugar onto the bees. Kits can be purchased online but are currently available from only one supplier, she said.

For more information on honey bees and varroa mites, got to the Bee Squad’s website, beelab.umn.edu. The site’s “Free-bee information” page includes step-by-step instructions to check colonies for varroa mites.

Masterman pointed to a varroa mite clinging to the back of a mature honey bee. The mite is a reddish dot on the bee’s thorax.

Bees are collected into a jar and covered in powdered sugar. The sugar doesn’t harm the bees, and the cornstarch added to the sugar helps the bees remove the mites.

Masterman shook the tiny parasites into a plastic jug. Varroa mites are a major threat to honey bees and can spread from hive to hive.