Honeybees responsible for pollinating crops worth billions of dollars are under attack from a cocktail of fungicides and pesticides that weaken colonies and make them susceptible to a deadly parasite, according to a study by the University of Maryland and federal agriculture researchers.
The report, published in the online scientific journal PLOS ONE this week, said contaminated pollen from seven different test crops on the East Coast reduced the ability of healthy bees to fend off a parasite that causes them to starve to death.
Researchers say this is the first study to demonstrate how the blending of pollen collected in the field and pesticides affect honeybee health.
"Our results show that beekeepers need to consider not only pesticide regimens of the fields in which they are placing their bees, but also spray programs near those fields that may contribute to pesticide drift onto weeds," said the study, funded by the National Honey Board and the U.S. Department of Agriculture.
However, the researchers stopped short of linking the chemicals to colony collapse disorder, a mysterious ailment that wipes out an entire hive in a short amount of time. Scientists and the beekeeping industry blame the disorder for destroying 10 million bee colonies across the country.
In Maryland, a robust honeybee population contributes to the prosperity of farms. State agriculture officials estimate that crops valued in excess of $40 million — apples, melons, berries and pumpkins — require or benefit from honeybee pollination.
The state has 1,782 registered beekeepers who together own more than 13,000 hives, also called colonies. Close to 60 percent of the managed hives across the state died last fall and over the winter.
The new study, begun four years ago, is an attempt to understand why bees are dying in record numbers.
A national report issued in May by the Bee Informed Partnership, a collaboration of state and federal agencies, confirmed that six of the last seven winters have been particularly deadly for honeybees.
"We've been working on the assumption that it's not one cause but several causes coming together. This work supports that theory, and it's one of the first studies to do this," said Dennis vanEngelsdorp, a research scientist at the University of Maryland and one of the report's authors.
Beekeepers brought their hives to crops to be pollinated. Researchers collected the pollen being returned to the hive, analyzed it for pesticides and then fed it to bees. Bees consuming contaminated pollen were significantly less able to resist a parasite called Nosema ceranae that impairs the digestion of pollen and, in effect, starves the bees.
Bees consuming pollen containing one fungicide were three times as likely to become infected by the parasite as those eating pollen without it.
"What's important about this in terms of what we can do is to make sure that insecticides are labeled so that farmers are told not to spray it when bees are foraging on flowering plants," vanEngelsdorp said. "Even more immediate is that beekeepers can work with farmers to say, 'Hey, when you're renting my bees to work your flowers, please don't spray during those times."
But that's small consolation for Maryland's beekeepers, most of whom do not rent their bees to farmers and keep colonies to produce honey for personal use or for sale at local produce stands.
Steve McDaniel, a Carroll County beekeeper for 35 years, said that while he applauded the research, he hopes it leads scientists to look at other potential culprits.
"They need to look beyond agriculture uses of these chemicals and look at home use," he said. "The directions on bottles of pesticides call for applications that are 40 times higher than what a farmer would be told to use."
McDaniel believes if scientists tested pollen taken directly from plants sprayed with household pesticides, "I bet you'll find it's enough to knock a bee dead on the spot."
A review of household pesticides and their use in urban and suburban areas would be "a very good thing," vanEngelsdorp said. Another step would be to review all the national data and try to develop a set of best practices for beekeepers to ensure healthier colonies.
McDaniel, the former president of the state beekeepers association, lost more than half of his bees last winter and is fighting to keep them alive this season.
"I can't afford to write off half of my bees again," he said. "No one can."
See the full study here.