According to Bross, about 200,000 bee colonies were killed and a similar number weakened during the winter.

The exact reasons are not known, and beekeepers are puzzled about what happens, the expert said. Some beekeepers will keep many hundreds of families at several sites.

At one location, the bees are healthy, while 10 kilometers away, at another site, they all died. "So it was not up to the beekeeper's expertise, as he managed both sites in the same way," Bross pointed out.