Dr. Nicholas Calderone, formerly part of Dr. H. Shimanki’s Beltsville research team at the Beltsville bee laboratory and now on the faculty of Cornell University has provided insight on integrated pest management (IPM) for Varroa mites. A synopsis of his work presented to the Canadian Association of Professional Apiculturists (Hive Lights, Canadian Honey Council, May 1996) was republished in The Speedy Bee (July 1996, Vol. 25, No. 7, pp. 1-2).
Dr. Calderone’s IPM strategy is to use a mix of methodologies to control Varroa populations. One is the use of what he calls “natural products” many of which can be called “oils.” These include tymol, eucalyptus, camphor and menthol. Research using this treatment showed good results in the fall, when most mites were on adult bees and little brood was present. When more brood was present, however, the treatment didn’t work as well, although it still had some effect. The difference in amount and kind of brood, depending on the season of the year, is always a key issue in Varroa control.
Two other methods used in conjunction with the natural products suggested by Dr. Calderone are mechanical. The first is the use of sticky boards. It seems that mites naturally fall off bees all the time and can return, unless they are physically trapped (stuck) on the boards. The final control measure is trapping mites in drone brood. In this method, drone foundation is inserted into the brood nest. When drawn out and populated with drone brood, the comb is removed and destroyed along with the mites that are trapped inside the sealed cells.
According to an article in Bee Science (Vol. 4, No. 1, 1996, pp 1-13 ), “Bio-technical manipulations used in Vietnam to control Varroa jacobsoni and Tropilaelaps clareae in colonies of Apis mellifera,” the latter method listed by Dr. Calderone is used when no chemical use is possible either because of cultural or economic reasons. In Vietnam, for example, corners of worker comb are cut off or empty frames are placed into colonies. When these are drawn out and populated with drone brood (preferred by Varroa over worker brood), they are removed and destroyed. In a variation of this technique, destruction of brood in conjunction with new queen introduction to provide a break in the brood cycle is also practiced. A variation of this is found in Dr. Zachary Wang’s MiteZapper, described along with other biocontrol methods by Contributor Randy Oliver.
Whether using essential natural products, essential oils, pesticides or mechanical control methods, The IPM principles discussed by Dr. Calderone above should always be kept in mind. This is especially true for chemicals. Employing any substance exclusively and/or to excess for Varroa control may lead to resistance and subsequent loss of the material as an effective control agent. Contributor Rusty Burlew says that rotation of chemicals is absolutely impertative.
A key ingredient in most IPM programs is sampling bee populations to determine the number of mites present. One technology to use that doesn’t kill honey bees is what is called the “sugar shake.” Only when this number exceeds a certain level is it generally considered wise to employ control measures. Unfortunately these levels are not set in stone and interpretation of the numbers is left to the beekeeper and vary significantly depending on season of the year. This is further complicated by possible rapid re-infestation from nearby untreated apiaries. Because of this it is easy to compromise IPM principles when attempting to control this pernicious mite.