MADISON, Wis. (AP) — Some Wisconsin beekeepers are reporting high losses of bees this winter because of a parasite that infests hives and kills developing bees.

Kent Pegorsch, president of the Wisconsin Honey Producers Association, told Wisconsin Public Radio that beekeepers had difficulty controlling varroa mites last year.

Beekeepers have been losing about half of their hives over the winter for the last five to 10 years, said Liz Meils, the state apiarist for the state Department of Agriculture, Trade and Consumer Protection.

"It's definitely significant and not really sustainable," Meils said. "The general consensus among beekeepers is that acceptable winter losses should be around 12 percent, up to 20 percent."

Producers can try to prevent loses by having their hives inspected and treated for mites, Meils said. The state has two inspectors from May to October who can inspect hives and give treatment advice, she said.

But some beekeepers are reluctant to treat for pests, Pegorsch said.

"Some of them would like to be treatment-free," he said. "But what happens is they actually cause their hives to what we say 'crash' from too many varroa mites in the hive. The hive crashes, the bees die and as that colony is crashing, the bees fly off and then they inhabit other colonies nearby transferring those varroa mites."

Beekeepers can recover from winter losses by bringing in new bees or splitting existing hives, Meils said.

But repopulating hives each spring can be challenge and financial burden, Pegorsch said.

The department is working to help producers who wish to keep their bees natural, Meils said.

"Beekeeping has become a lot more hands-on, and treatment-free is not really feasible anymore," she said. "But there are a lot of natural and organic options that are available to help the bees survive these mites.