Honey bee colonies at heightened risk of collapse in the Pacific Northwest: Study

Climate change-induced warming may be jeopardizing the survival of honey bee colonies in the Pacific Northwest, a new study has found.

Contributing to this threat is an increasingly long autumn season, which is extending the amount of fall flying weather but is wearing out worker bees for spring, according to the study, published Monday in Scientific Reports.

Worker bees seek out flowers whenever the weather is suitable, no matter how much honey is already in their hives, the authors explained. But flying also shortens the lives of bees, they noted.

“This is a case where a small amount of warming, even in the near future, will make a big impact on honey bees,” lead author Kirti Rajagopalan, a Washington State University climate researcher, said in a statement.

“It’s not like this is something that can be expected 80 years from now,” Rajagopalan continued. “It is a more immediate impact that needs to be planned for.”

To explore this phenomenon, the researchers conducted simulations that explored honey bee population dynamics and incorporated climate projections for 2020 and 2100.

They found that Pacific Northwest colonies would likely endure spring collapses in both the near- and long-term cases. This outcome applied both to scenarios in which climate change progressed according to today’s trajectories and to those with reduced greenhouse gas emissions.

Worker bees tend to forage for food whenever temperatures climb above 50 degrees Fahrenheit, the authors noted. When the weather is colder, the bees huddle in the hive, eating honey and shivering to keep warm.

As spring begins, the adult worker bees begin flying again, which also means they start dying, the researchers explained. But if too many older worker bees have already died before their replacements are ready to fly, the entire colony can collapse, the authors warned.

Colonies that winter outside in colder areas in the far north of Washington State might be able persist despite the impacts of climate change, according to the study.

However, spring hive populations closer to the Oregon border could plunge below 9,000 adults by 2050 and below 5,000 by the end of the century, the researchers found. Colony collapse, they explained, can happen when there are fewer than 5,000 to 9,000 adult bees in a hive.

“Even if there is no nutritional stress, no pathogens, no pesticides — just the conditions in fall and winter are enough to compromise the age structure of a colony,” said co-author Gloria DeGrandi-Hoffman, of the U.S. Department of Agriculture’s Carl Hayden Bee Research Center, in a statement. 

“When the hive comes out of winter, the bees are dying faster than they’re being born,” DeGrandi-Hoffman added.

But the scientists did also provide some room for hope, by exploring certain climate adaptation measures that could be undertaken to mitigate risk.

The scientists decided to simulate a relatively new technique called “cold storage,” in which honey bee hive boxes are placed in cold indoor facilities. They found this method would enable bees to start clustering earlier and, in the process, save the lives of workers.

The models looked at the impacts of moving hive boxes from the Washington-Oregon border area into cold storage beginning in mid-October.

Hypothetical releases then occurred either April 1, when pollen starts becoming available in the Pacific Northwest, or Jan. 31, when more than a million hives are shuttled to California to pollinate almonds. 

Although both cases generated larger populations than outdoor baseline conditions, the April 1 releases led to stronger growth, because brood-rearing tends to begin in late January, per the study.

“While autumn has historically been a time of preparation for winter hibernation and confinement, climate change is making it a crucible that defines the ranges and diversity of species across habitats,” the authors stated. 

“The success of the management schemes will have broad implications for the socio-economic viability of the beekeeping industry, the production of crops that rely on honey bee pollination, and food and nutritional security,” they concluded.