The mysterious die-off of honey bees continues, as beekepers across the nation lost more than one in three of their colonies since last spring, researchers reported Thursday. The losses in Maryland were even more extreme, where nearly half were lost, according to the state's chief apiary inspector.
The national survey of beekeepers found that they lost one in five honey bee colonies over the winter, fewer than the winter before. But they reported seeing substantial die-off in summer as well, pushing their year-round losses to more than a third.
The annual survey, led by a University of Maryland entomologist, is part of an effort to get to the bottom of high death rates that commercial beekeepers have experienced for nearly a decade. The losses impose high costs on beekeepers and could lead to shortages of some crops that depend on honey bees for pollination, experts say.
While many beekeepers and some researchers have linked the die-off to pesticide exposures, the team that did the survey say no single culprit is responsible for all the honey bee deaths. But Dennis vanEngelsdorp, the UM assistant professor of entomology who led the survey team, said mortality was much lower among beekeepers who treated their hives to control a common but lethal parasite, the varroa mite.
Researchers surveyed nearly 7,200 beekeepers, who collectively manage about a fifth of the nation's 2.6 million commercial honey bee colonies. It was conducted for the Bee Informed Partnership, a joint effort of the Apiary Inspectors of America and the U.S. Department of Agriculture.
In Maryland, Jerry Fischer, chief apiary inspector with the Maryland Department of Agriculture, said the state's beekeepers have been losing about a third of their colonies annually for several years. The rate increased in the past year to nearly 50 percent, he said, which he blamed on an unusually cold winter.
"It was about the worst winter we've had in the past 20 years, for bee management and surviving bees," Fischer said.
Overall, though, the state apiarist attributed 80 percent of honey bee losses in the state to the inexperience of the state's mostly part-time beekeepers, rather than pesticides, mites or any other outside factor.
Fischer said there are just four large commercial beekeeping operations in the state. The vast majority of Maryland's 1,851 registered beekeepers are what he calls "hobbyists," for whom tending honey bees is not a full-time livelihood. They manage 14,000 colonies, he said, with nearly two thirds having two or fewer colonies.
Many of the colonies he inspected late last summer appeared not to have stored up adequate honey supplies to survive the winter, he said.
But longtime beekeeper Steve McDaniel in Carroll County said he believes the pattern of die-off he's seen still implicates widespread use of pesticides containing neonicotinoids, a nerve agent. Some pesticides sold for homeowners' use contain it, he said.
Preliminary results of a survey he conducted of central Maryland beekeepers found colonies in urban and suburban areas 3.5 times more likely to die than those in rural and farm areas. Of 21 participating beekeepers, a third of their 130 colonies were lost in the past year. The loss rate reached 52 percent among suburban colonies, with only 15 percent losses in farm and rural areas.
McDaniel, a retired chemist who's been keeping bees for 36 years, said he lost two-thirds of the 20 colonies he had at this time last year. In early March, he said, he suddenly lost "a big strapping colony of bees" that appeared to be doing fine with ample food. When he returned to check the hive a week later, he saw "piles of dead bees, inside and out."
A new study conducted at the Harvard School of Public Health and published in the Bulletin of Insectology found that two widely used neonicotinoid pesticides appear to "significantly harm honey bee colonies over the winter." The colder the winter, the more severe the harm, the study's authors suggested.
The study echoed a 2012 finding of a link between low doses of one neonicotinoid compound and "Colony Collapse Disorder," which that makes bees abandon their hives and die. A second pesticide had the same effect, Harvard researchers found.