Over 40% of US honeybee colonies died off in the last year

This post has been corrected.

40% of US honeybee colonies were lost in the past 12 months, continuing a troubling spike in bee mortality over the past decade, according to the US Agricultural Research Service’s annual bee survey. And scientists still aren’t sure why.

It’s normal for some bee colonies to perish over the course of a year. Surveyed beekeepers reported that a tolerable amount of colony loss was 18.7% this year. Two-thirds of them suffered losses greater than this number. Overall, 42.1% of colonies died off between April 2014 and April 2015.

The high death rates in recent years have been an economic challenge for beekeepers and worrisome to the farmers who depend on the insects for pollination of $15 billion of crops each year, the Wall Street Journal reports.

Typically, winter has been the most harrowing time for colonies. But in recent years, winter losses have fallen, while summer has emerged as a trying time as well. This year, for the first time since summer loss data has been collected, more losses occurred in summer than in winter.

Summer_honeybee_colony_loss_surpassed_winter_for_the_first_time_Winter_losses_Summer_losses_chartbuilder

Nobody knows quite what’s killing the bees. The crisis began in 2006, when a number of US honeybee colonies were stricken with Colony Collapse Disorder (CCD), a strange societal disease in which most of a colony’s worker bees flee the hive, leaving it high and dry. CCD could annihilate as much as 90% of a colony.

The good news is that in recent years, CCD hasn’t caused much of a problem. But still, losses have remained high.

“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,” said USDA entomologist Jeff Pettis.

There are likely a number of factors at play: pesticides, poor hive nutrition, mite infestations. But the strange results of this year’s survey underscore once again that we just don’t really know what’s happening to American bees.

Correction (May 14, 2015 3:20 p.m.): An earlier version of this article suggested that 42.1% of US honeybees died in the past year. It has been changed to clarify that 42.1% of honeybee colonies were lost.

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