LINCOLN, Neb. -- The varroa mite is a major pest of honeybees worldwide, but a chemical naturally found in plants such as rhubarb, turnips and broccoli can help deter the mite populations from establishing in bee colonies.

Oxalic acid, which makes the vegetation nonpalatable to insects, will help struggling beekeepers keep their hives healthy and stay economically profitable, said Marion Ellis, University of Nebraska-Lincoln entomologist. Once varroa mites enter bee colonies, they build up to damaging levels, causing bee hives to perish without human intervention.

"Hopefully, it will become another tool for helping beekeepers," Ellis said. "It's a natural product, it's low cost, sustainable and it's effective. In addition, it doesn't leave residue in hive products and is readily available and biodegradable."

While some strategies to control the mites already exist, they are labor-intensive, and mites have become resistant to many available chemical treatments.

The Institute of Agriculture and Natural Resources researcher is testing oxalic acid's chemical efficacy and ways to use it. Varroa mite control often is difficult because honeybees and varroa mites are so closely related.

Since the mites and the bees are both arthropods, what kills the mites can kill the bees. Toxicological studies are being fine-tuned to find the dose necessary to kill mites, but not bees.

The Midwest is a prime honey-producing area. However, most beekeepers' principle source of income is the use of their bee hives for crop pollination. Of the 1.5 million bee colonies in the U.S., 1.4 million are needed to pollinate crops, Ellis said.

"The varroa mite has caused beekeepers to lose half or more of their colonies," he said. The average beekeeper might have 1,500 colonies and each colony is worth about $120.
In states such as California, Texas and Florida, insect-pollinated crops are a significant part of agriculture. Because of the varroa mite, beekeepers have been unable to meet the bee colony demands on these farms, which are expanding, Ellis said.

One of the main forces behind this expansion is the increase in almond acres in California, he said.

Entomologists also are looking at ways to eliminate mites in mail shipments and ways to eliminate mites in colonies in the winter when there are no broods and the mites are attacking adult bees.

Entomologists also will develop extension publications and conduct training for the new product's use.

These studies are funded by the EPA in cooperation with IANR's Agricultural Research Division.

SOURCE: University of Nebraska news release.