College of Agricultural, Human, and Natural Resource Sciences

Researchers feed, breed, protect bees to survive winter

WSU technician Philip Baker examines a hive this fall.
WSU technician Philip Baker examines a hive this fall.

Gathering last-minute sips of nectar and pollen, bees at the Washington State University Teaching Apiary recently made the most of an unusually warm, 60-degree November day.

So did bee breeder Steve Sheppard, who helped winterize dozens of WSU research hives before the cold returned.

“We’re lucky to have this kind of weather,” said Sheppard, who has led the university’s bee breeding program for 18 years. “A month from now, we wouldn’t be able to do this.”

Feeding bees, fending off disease

Winter is a tough time for the world’s most important pollinator. In addition to frigid temperatures, honey bee colonies must battle disease and parasites, including the devastating Varroa mite. WSU researchers are trying to help bees fight off these threats and survive until spring.

“We are breeding bees that overwinter in a thrifty fashion and resist disease,” said Sheppard. “We’re trying to develop bees that thrive without antibiotic treatment and with reduced mite treatments.”

In the teaching apiary, Sheppard and technician Philip Baker move from hive to hive, lifting lids to check the buzzing occupants for disease and hefting the double-decker wooden boxes to gauge their weight. A healthy hive contains at least 80-90 pounds of stored honey for the winter.

Entomologist Steve Sheppard checks colony health in the WSU Teaching Apiary.
Entomologist Steve Sheppard checks colony health in the WSU Teaching Apiary.

To help underweight hives, Baker and WSU entomology students will place feeders full of thick sugar syrup inside. Timing is essential – once the temperature drops, bees aren’t able to easily access feeders: “If you don’t have your bees ready when winter comes, there’s not a lot you can do to fix it,” said Sheppard.

Winter bees cluster for warmth

In autumn, there’s a changing of the guard inside beehives where a new, longer-lived generation of bees is born. “Winter bees,” born with higher levels of fat and protein reserves, look the same as their summer siblings but far outlast hard-working summer bees, who only live as long as six weeks.

When outside temperatures fall below 55 degrees, bees form a “winter cluster,” packing tightly together and vibrating their wing muscles to keep warm.

“They’ll cluster for weeks or even months,” said Sheppard, which keeps the core of the hive a toasty 75 degrees.

When daytime temperatures rise above 55, winter bees take a “cleansing flight,” eliminating wastes.

“The cleansing flight is most noticeable after a number of weeks or months when they can’t fly,” said Sheppard. “When it warms up, the cluster dissipates and bees are able to fly again.”

Protecting hives from rotting, rodents

Among winterizing duties, Baker ensured that every hive is raised off the ground and every entrance angles downhill to drain rainfall and prevent rotting. He installed wire mesh screens in the entrances to ensure mice can’t come inside – a fast-multiplying rodent nest means quick doom for a dormant bee colony – and removed the entrance reducers that have protected the hive from wasp predators in late summer.

Bees forage on a warm November day. Screens protect the hive from intruders, but must be removed before winter.
Bees forage on a warm November day. Screens protect the hive from intruders, but must be removed before winter.

“These are dangerous to keep on in winter,” said Sheppard. Entrance reducers increase the danger of blockage and suffocation during the clustering period.

“There shouldn’t be many drones left,” he said. Not needed for mating in winter, male bees are useless mouths driven out of the hive by workers every autumn. Bees stop rearing brood in fall and queens won’t start laying eggs again until after the solstice, when days start to lengthen. New baby bees will be fed stored honey and pollen.

New research center would study overwintering

WSU entomologists keep more than 200 hives on the Pullman campus and on surrounding properties in Washington and Idaho.

“To facilitate our field research, we can always use more bees,” said Sheppard. His team often partners with commercial beekeepers across the state to conduct research with their hives.

The proposed WSU Honey Bee and Pollinator Research Facility would permit increased hive numbers and infrastructure to expand research on honey bees and other pollinators.

“The new center increases our capacity in several areas,” Sheppard said. “All of our researchers, labs and workshops would be in one location. The facility would also contain the country’s first controlled atmosphere rooms dedicated to studying overwintering in bees.”

Inside a hive at the teaching apiary. Winter brings workers back to the hive to cluster for warmth.
Inside a hive at the teaching apiary. Winter brings workers back to the hive to cluster for warmth.

Pioneering controlled climates for bees

Sheppard’s program has broken ground in incorporating controlled climates for better overwintering. Inside old apple storage warehouses, bees are kept in rooms containing up to 5,000 colonies with elevated carbon dioxide concentrations. The bees aren’t harmed by the CO2 but there is evidence that it can help control mites.

Sheppard’s lab has recently found that bees from colonies wintered indoors exhibit improved lipid and protein levels compared to those wintered outdoors. The success of indoor wintering has already changed the overwintering practices of some beekeepers, and facilities are being built in a number of western states.

WSU entomologists are also continuing experiments with a fungus called Metarhizium anisopliae, which is known to kill Varroa mites. Scientists seek to learn whether the fungus is more effective in winter.

“Metarhizium is sensitive to dryness and heat, which has been a limitation in summer use,” said Sheppard. “We are selecting strains that show improved virulence against mites and will be testing them for winter use.”

Learn more about the WSU bee program and the proposed new bee center at

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“Well, if I’m going to be the favorite senior,” Carter said to himself, “I’d better start taking some ag classes.”…

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