More than 40 percent of U.S. honeybee colonies died over the course of the past year, according to an annual U.S. Department of Agriculture survey conducted by researchers from institutions including the University of Maryland and the University of Georgia.
Shockingly, the worst die-off occurred in the summer, which is typically a good time of year for bees. Most die-offs take place in the winter months, which tend to be more stressful for bees.
“What we’re seeing with this bee problem is just a loud signal that there’s some bad things happening with our agro-ecosystems,” co-author Keith Delaplane said. “We just happen to notice it with the honeybee because they are so easy to count.”
Die-offs shift from winter to summer
Last year’s survey seemed to indicate a slowdown in the ongoing crash of honeybee populations. That survey showed a 23 percent loss of honeybee colonies, compared with the 30 percent that was average between 2005 and 2013. The same year, beekeepers began to report progress in the battle against the varroa mite, a parasite that has devastated commercial hives.
Researchers warned at the time against celebrating too soon.
“One year does not make a trend,” said Jeff Pettis, co-author of that survey and head of the federal bee research laboratory in Beltsville, Md.
Pettis’ caution turned out to be well founded. According to the new survey, 42.1 percent of colonies died between April 2014 and April 2015, which is the second highest rate of loss in nine years.
Alarmingly, this year marked the first time that the majority of colony deaths took place during the summer. Beekeepers reported losing 27.4 percent of their colonies over the summer, which is much higher than the 19.8 percent noted the year before.
Such a pattern is “unheard of,” said researcher Dennis van Engelsdorp, who likened it to seeing “a higher rate of flu deaths in the summer than winter. You just don’t expect colonies to die at this rate in the summer.”
“We traditionally thought of winter losses as a more important indicator of health, because surviving the cold winter months is a crucial test for any bee colony,” van Engelsdorp said. “But we now know that summer loss rates are significant too. This is especially so for commercial beekeepers, who are now losing more colonies in the summertime compared to the winter.”
Beehive losses were greatest in Delaware, Illinois, Iowa, Maine, Maryland, Oklahoma and Wisconsin, which each lost more than 60 percent of their hives.
“The winter loss numbers are more hopeful especially combined with the fact that we have not seen much sign of Colony Collapse Disorder (CCD) for several years, but such high colony losses in the summer and year-round remain very troubling,” Pettis said
Pesticides, habitat loss likely to blame
Dick Rogers, chief beekeeper for pesticide-and-pharmaceutical giant Bayer, tried to downplay the losses, noting that there were actually more colonies in April 2015 than there were at the same time last year. Delaplane responded that such numbers are deceptive because after colonies die, beekeepers typically split their existing colonies to make up for the loss. These new, smaller colonies are not necessarily healthy.
Bayer’s desire to dismiss the die-off is understandable given how much attention has focused in recent years on pesticides as a likely culprit in collapsing pollinator populations worldwide. In particular, scientists have warned of a popular pesticide family known as neonicotinoids. The European Commission has already banned three neonicotinoids due to concerns about pollinator impact.
Van Engelsdorp also blames poor nutrition for the declining populations of pollinators, including honeybees. He noted that the vast areas of land formerly covered by the wildflowers that pollinators use for food have been disappearing as more land is converted to agriculture to take advantage of rising food prices. Since 2007 alone, the land retained by the Agriculture Department for conservation has been halved and continues to shrink.