Note #3b
VARROA MITES
INTRODUCTION
The Varroa mite (Varroa jacobsoni) is the most serious of the bee pests confronting beekeepers in the U.S. and throughout the Americas. The mite was first detected in the U.S. in 1987 (in Florida and Wisconsin) and subsequently detected in North Carolina in 1990. Since its establishment in N.C. and the U.S., the mite has killed at least 1/3 of the managed honey bee colonies and almost all of the wild (feral) honey bee colonies. Left untreated the mites will kill the typical bee colony within one to three years with colonies in the southern U.S dying quicker than those further north. In N.C. the mites will usually kill a bee colony within one to two years if the colony is not properly treated using an authorized chemical treatment.
MITE BIOLOGY
The mite is an external parasite which attacks both adult bees and the developing honey bee larvae. The adult mites have a flattened oval shape, are reddish-brown in color, and are about .06 inches wide (about the size of the head of a pin). Figure 1 shows the life cycle of the mite.
The mated female mite enters the cell of a developing bee larva and lays up to six mite eggs. The developing mites feed on the larvae and depending on the number of mites may kill it, cause it to be deformed, or have no visible effect.
The new adult female mites (the males die in the cell) climb onto an adult worker bee and feed on its hemolymph (blood). The female mite then can repeat the cycle by entering cells of other developing bee larvae. Mites prefer drone larvae over worker larvae, but they will infest worker larvae and eventually kill the colony if not treated.
The mites can kill the bees in several ways. In addition to the obvious effects of multiple mites feeding on bees, there is also the problem that the mites can spread various viruses that can kill bees. The various viruses can cause a condition referred to as Parasitic Mite Syndrome PMS). Treatment involves killing the mites which spread the viruses.
DETECTION AND TREATMENT
Many of the bee colonies that are going to die from varroa mite infestations will do so in late summer or later in the calendar year. It is very difficult to simply observe a colony and determine if it has a high level of mites. Colonies that appear to have large bee populations and that have made good honey surpluses may suddenly collapse in August or September depending on your location in the state. Under current conditions in N.C., our recommendation is to routinely treat all honey bee colonies in the Spring and the Fall with labeled chemical products.
If you wish to avoid chemical treatments, then you can sample the mite levels in your bee colonies and determine if treatment is necessary. Following are two detection methods:
1. Alcohol Role Method: Brush or shake about 300 adult bees into a clear container containing about 1 1/2 inches of alcohol. Vigorously shake the container for at least 30 seconds, and then examine the container for dead mites sticking to the inside surface. If you see 15 or more mites then you should treat the colony. Results from this test can vary, and the next detection method is more reliable.
2. Sticky Board (Mite Census) Method: Make or purchase a commercial sticky board that will cover the hive's bottom board. Sticky boards may be made by placing a stiff sheet of white paper between two 8 mesh wire covers (top and bottom of paper). The upper surface of the paper (facing the bees) should be sprayed with one of the aerosol cooking sprays. The theory is that the mites that fall off the bees (on a routine basis) will fall through the screen cover and stick to the white paper that is coated with cooking spray. The bees will not be able to reach the paper through the 8 mesh screen. Place the sticky board in the hive for 24 hours and then examine it. If you find more than 115 mites, then you should treat the colony.
Chemical (Pesticide) Treatment:
At the present time two pesticides have frill registration by the U.S. Environmental Protection Agency for the control of varroa mites.
Apistan TM, the trade name for fluvalinate (pyrethroid) is sold in a plastic strip form that is impregnated with the active pesticide. Apistan is a contact pesticide and provides up to 1OO% control (kill) of varroa mites when properly used. There have been documented cases of varroa mites developing resistance to this pesticide, but that is not a serious problem in N.C. at this time. However, it is recommended that the use of Apistan be rotated with the use of formic acid (see next product) to reduce the development of resistance to chemical control by the mites. The consistent use of one chemical product is more likely to result in the development of resistance by the pest than is the use of two different products on a rotating basis.
Apicure TM is the trade name for formic acid. This product is sold in a gel form enclosed in a plastic pouch. The formic acid vaporizes and works as a fumigant in the hive. This product is not as effective as Apistan in controlling varroa mites (kills about 75% of the mites), but it has two advantages. Apicure also will control tracheal mites and is a naturally occurring product in honey.
Recommended Chemical (Pesticide) Treatments:
Unless the beekeeper is sampling the bee colonies for mite levels, it is recommended that the following routine treatments be made to insure the survival of the honey bees:
Spring (late winter/early spring) Treatment:
Treat the bee colonies with Apistan for varroa mite control. If there is concern about tracheal mite levels, then the beekeeper should consult his/her local NCDA bee inspector or the Extension Apiculturist's Office about combining menthol (Mite-A-Thol TM) with the Apistan treatment or replacing the Apistan treatment with an Apicure treatment.
Apistan must be removed from the beehives prior to the start of the main honey flow and treatment time is 56 days (8 weeks) to insure that all of the mites on any capped brood are killed after the new adult bees have emerged. Determine the date of the start of your main honey flow and start your Apistan treatment at least eight weeks prior to that date. If you have been sampling your bees for mite levels and decided not to use a Spring treatment, then be sure to continue sampling your colonies for varroa mites to determine if a treatment is necessary later in the season. Remember that honey collected by your bees during Apistan treatment may not be used for human consumption.
Fall (late summer/early fall) Treatment:
Treat the bee colonies with Apicure (formic acid) for varroa and tracheal mites. Apicure is most effective in controlling tracheal mites (as good as menthol, the other labeled product for tracheal mite control) if used when brood is at a minimum. This recommended alternating use of formic acid in the fall with fluvalinate (Apistan) in the spring will benefit N.C. beekeepers in delaying the development of resistance by varroa mites to either treatment. Apistan in the spring and Apicure in the fall provides for the effective use of both products.
The actual start date of Apicure will vary from region to region of the state, but a good event date is when your bees start to throw drones out of the hive which may be as early as late July in some localities. Formic acid should not be used when the bees are making a honey surplus so the start date for treatment in areas that make sourwood honey should be delayed until the honey crop is made by the bees and then removed from the hive. Formic acid can cause the honey to have an objectionable taste and odor. Because formic acid works as a fumigant, it is temperature dependent and not effective at temperatures below 45 degrees F.
Special Notes on Chemical (Pesticide) Treatments:
1. Varroa infested bee colonies that are not chemically treated will probably die and that loss may occur within the first year of infection by the parasite.
2. At the present time there are two pesticides that have frill (general) registration by the U.S. Environmental Protection Agency (EPA) for the treatment of varroa mites - Apistan (fluvalinate) and Apicure (formic acid).
3. N.C. does have a special exemption from the EPA to use an additional product (coumaphos) which is sold under the trade name of CheckMite TM. That product is presently recommended only for the treatment of small hive beetles in NC. Coumaphos is a member of the organophosphate group of pesticides and its sale in NC is restricted to those individuals who have a Pest Control License since the product is a restricted use pesticide.
4. Read and follow all label directions on pesticide usage.
5. Research is underway on various non-chemical treatments of vatroa mites, but none of those treatments or combinations of those treatments are as effective as the labeled chemical treatments. The following non-chemical treatments are available to beekeepers but their use in only recommended in conjunction with efficient mite sampling procedures and approved chemical treatments:
Mite "Resistant" Queens, Recessed and other special bottom board designs, drone brood frames, sticky boards, essential oils, and pollen traps.
6. Do NOT under any circumstance experiment with non-approved chemical treatments. Such practices may result in bee death and/or the contamination of your honey and wax.
7. For additional information or assistance, contact your local NCDA bee inspector, your local county Cooperative Extension Office, or the Apicultural Office at NCSU and our web site at http://www.ces.ncsu.edu/Insects/Bees
Prepared by: John T. Ambrose, Extension Apiculturist August 1999, Major Revision in April 2000 ebj/d2
Recommendations for the use of chemicals are included in this publication as a convenience to the reader: The use of brand names and any mention or listing of commercial products or services in this publication does not imply endorsement by the North Carolina Cooperative Extension Service nor discrimination against similar products or services not mentioned. Individuals who use chemicals are responsible for ensuring that the intended use complies with current regulations and conforms to the product label. Be sure to obtain current information about usage and examine a current product label before applying any chemical. For assistance, contact an agent of the North Carolina Cooperative Extension Service.
