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More than two out of five American honeybee colonies died in the past year, and surprisingly the worst die-off was in the summer, according to a federal survey.

Since April 2014, beekeepers lost 42.1 percent of their colonies, the second highest loss rate in nine years, according to an annual survey conducted by a bee partnership that includes the U.S. Department of Agriculture.

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"What we're seeing with this bee problem is just a loud signal that there's some bad things happening with our agro-ecosystems," said study co-author Keith Delaplane at the University of Georgia.

But it's not quite as dire as it sounds. That's because after a colony dies, beekeepers then split their surviving colonies, start new ones, and the numbers go back up again, said Delaplane and study co-author Dennis vanEngelsdorp of the University of Maryland.

What shocked the entomologists is that is the first time they've noticed bees dying more in the summer than the winter, said vanEngelsdorp said. The survey found beekeepers lost 27.4 percent of their colonies this summer. That's up from 19.8 percent the previous summer.

Seeing massive colony losses in summer is like seeing "a higher rate of flu deaths in the summer than winter," vanEngelsdorp said. "You just don't expect colonies to die at this rate in the summer."

IN-DEPTH

--- The Associated Press