As part of a panel on parasitic mites at the American Beekeeping Federation Meeting in Austin, TX, January 18, 1995, Dr. Anita Collins of the Weslaco, TX ARS Bee Laboratory provided an overview of current treatments available to the beekeeping industry. Menthol is for tracheal mites, but has its limitations. The temperature conditions and placement of the material in a hive required to vaporize the correct amount of fumigant are extremely variable. Apistan® continues to be the preferred treatment for Varroa, according to Dr. Collins. It relies on physical transfer of the active ingredient (fluvalinate) from plastic strip to bee and finally to mite. There are efforts underway, Dr. Collins concluded, to have an alternative material, formic acid, registered for mite control. It is presently registered in Canada and there seems a good likelihood that this can also be accomplished in the U.S.

Dr. Marion Ellis, new Secretary-Treasurer of the American Association of Professional Apiculturists (AAPA) said it is impossible to treat for every Varroa mite. The only logical strategy, he said, is not only to monitor the bees themselves, but also to take other factors into consideration when determining mite population levels. Of particular importance, Dr. Ellis said, is the changing ratio of bees to mites during the active season. Early in the year, the bee population can often outrun that of the mites; treating then may not produce optimal results. Later in the season, however, when bee populations fall off, the Varroa population can quickly outstrip the bee population, and multiple infestations of single bees may occur. Waiting too long during this period will cause colony death.

Thus, the mite/adult bee ratio is a key detection index, Dr. Ellis said, and when 30 to 40 percent of bees have one adult Varroa on them, the bees' colony structure begins to collapse. Dr. Ellis concluded his remarks with an impassioned plea for beekeepers to protect the only product, Apistan®, that is registered, legal and effective to control Varroa. This means assiduously avoiding abuse of the material (leaving the strips in too long; treating at inappropriate times; not following the dosage recommendations on the label; and reusing strips) and not using unregistered, illegal formulations of fluvalinate. Incorrect use of fluvalinate could result in removal of the product by regulatory authorities and/or rapid buildup of mite resistance.

This warning was also voiced by Oscar Coindreau, representative of Apistan's® manufacturer, Sandoz Agro. He reported that Varroa resistance to fluvalinate has already been found in Italy. This occurrence has been linked to using the formulation known in Europe as Klartan®.

Wooden strips, paper towels and cloth rags dipped in commercial solutions of fluvalinate give off the pesticide more quickly and in greater amounts than does Apistan®, Mr. Coindreau said. When this occurs, control of Varroa is irregular which can cause resistance to build up in mite populations. These practices also contaminate wax and honey. According to Mr. Coindreau, fluvalinate, as formulated in Apistan®, has little opportunity to contaminate honey because the plastic slowly releases the material into a colony. In addition, fluvalinate is hydrophobic, and not soluble in honey, although it can contaminate wax over time. In contrast, other formulations like Maverik®, sold in the U.S., and Kartan® have surfactants and emulsifiers that permit honey to be contaminated along with wax.

A key fact, Mr. Coindreau said, is that not much resistance by Varroa is required to render Apistan® ineffective. Killing any less than 99 percent of the mite population is in reality no control, because the mites rebound so quickly, especially in a populous bee colonies. This makes it critical to protect the product from being abused in the field.

Although mite treatments are in place, Dr. Shimanuki of the Beltsville Bee Laboratory, Beltsville, MD, said in concluded the panel, there is evidence that mite-bee interactions in themselves can result in other problems now being found in honey bee colonies. Samples coming into the Beltsville laboratory are showing signs of what appears to be American foulbrood, but the causitive organism, Bacillus larvae, is absent. These could be the results of a viral infection, Dr. Shimanuki said, but none have been isolated from these samples.

Unfortunately, Dr. Shimanuki told those in attendance, only a very few laboratories worldwide are working on bee viruses. In the meantime, he and those at his laboratory, have coined a temporary name, "parasitic mite syndrome," because mites are invariably associated with the symptoms. And although apparently a viral disease, bee colonies are helped by treating with Terramycin® and Apistan®, as well as feeding sugar syrup, none of which are known treatments for conditions caused by viruses.

Possible causes of parasitic mite syndrome, Dr. Shimanuki said, are Kashmir bee virus or acute paralysis bee virus. It is not known how much Kasmir bee virus is present in the U.S., but there have been confirmed cases in Florida and California. This virus is known to be latent, appearing only after adult bees are injured (mite feeding?), and it also affects larvae. Acute paralysis bee virus has no specific symptoms and may also be triggered by the trauma of mite parasitism. Until more is known about this situation, Dr. Shimanuki concluded, the only recommendation at present is to reduce the incidence of this disease by controlling mite populations with registered treatments.