How to Smite Bee-Killing Mites? Maybe Mint Oils

It sounds like a folk remedy, but a West Virginia University entomologist says it works: Use natural oils--spearmint, wintergreen, peppermint--to ward off mites preying on wild honeybees.

The proof, James Amrine says, can be seen in 46 nearby honeybee colonies where applications of wintergreen have produced the healthiest honeybees in years.

“There is no doubt those bees are almost back to where they were before these mites came into this country,” he said.

The mites, which entered the United States 12 years ago, have destroyed 90% of wild honeybees, researchers say.

Last spring, commercial and hobbyist beekeepers reported average losses of 50% in 22 states surveyed by the Georgia-based American Beekeeping Federation, said Troy H. Fore Jr., executive secretary.

The harsh winter contributed to losses, especially in northern tier states like Maine, which reported 80% losses.

The losses follow a continual weakening of honeybees since the mites appeared in the mid-1980s.

The original invader, the tiny tracheal mite, crawls into the breathing tubes of bees and lives off their blood. The varroa mite, the size of a small tick, attaches to bee adults and developing eggs and lives off their blood, weakening and killing them.

In Cumberland, Md., about 60 miles east of Morgantown, Bob Noel stumbled upon his natural-oils remedy when mites struck his colonies last year. He put wintergreen oil in a hamburger-patty-shaped mixture of shortening and sugar, then placed it in a hive.

“I said, ‘Well, they’re dying anyway.’ I came back a couple of days later and there were no mites on the bees. There were several thousand [dead] mites on the bottom of the hive,” he said.

That inspired tests of natural oils like tea tree, pennyroyal, patchouli, spearmint and peppermint. Noel also plans to try lavender. He thinks most mint oils will work.

Amrine was skeptical, but he could not argue with the results. Noel’s honeybees are healthy and producing up to 150 pounds of honey for the season in each hive.

“Most of the beekeepers around the United States would be envious of his hives,” said Amrine, whose research centers on the most effective way to apply mint oils to the bees.

Amrine said one of Noel’s more effective methods consists of putting a greasy salve of wintergreen on a “tracking strip” that comes into contact with bees. And Noel is working on an advanced version that is constantly replenished by a feeder.

Another method involves a mixture of sugar water and mint oils the bees drink when flowers are not producing nectar. Then there are the so-called “grease patties,” which are placed in hives.

Under the systems, the bees come into contact with the messy mixture and ingest it when they clean themselves. During winter months, they will consume the grease patties to get the sugar.

The mint kills and weakens varroa mites and renders them unable to reproduce, Amrine said. Tracheal mites get trapped in the oil and die because they cannot get into bees’ breathing tubes, he said.

Amrine is so confident in the preliminary findings that he has posted the formulas on the Internet so beekeepers can begin using them.

“We’re close to eradication where we can knock them out totally,” he said. “We’re going to continue working in that direction: total eradication.”

Beekeepers elsewhere are following Noel’s lead.

Wholesaler Lorann Oils in Lansing, Mich., says its sales of natural oils have grown 10% to 15% since beekeepers started calling for supplies. John Grettenberger, general manager, said the company recently ran out of pennyroyal oil because of the demand.

Anita Collins, a research geneticist at the U.S. Department of Agriculture’s bee research lab in Beltsville, Md., said the research into natural oils is important because mites have developed resistance to the only pesticide available. The oils, if effective, might be preferable to traditional chemical pesticides.

Meanwhile, scientists are continuing the lengthy process of developing mite-resistant bees. But Collins said she cannot blame beekeepers for tinkering with mint oils.

“There’s a lot of them who have lost bees and they’re ready to try anything,” she said. “The other choice is to lose their bees.”