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Producing Varroa-Tolerant Honey Bees from Locally Adapted Stock: A Recipe*

By E.H. ERICKSON, L.H. HINES, and A.H. ATMOWIDJOJO
Carl Hayden Bee Research Center
2000 E. Allen Road
Tucson, AZ 85719

*Mention of a proprietary product does not constitute its endorsement by USDA-ARS over that of any other like product.

Abstract
Our earlier research demonstrated that it is relatively easy for beekeepers in the southwestern United States to produce Varroa-tolerant honey bee populations using their own locally adapted stock. The only requirements are fundamental beekeeping skills, the ability to rear queens, and the few Varroa-tolerant colonies that are present in nearly every apiary. Our Varroa-tolerant population was developed in less than 2 years and is now going into its sixth year. An easy-to-understand recipe that any beekeeper can use to produce Varroa-tolerant stock is presented. Our purpose is to encourage beekeepers elsewhere to undertake a similar effort in order to determine the universality of application of our findings.

Introduction

Since 1994 we have been engaged in a long-term study to determine whether locally adapted Varroa-tolerant honey bee populations could be developed, maintained, and expanded via selective breeding and conventional beekeeping practices, and without the use of other mite control strategies. The results of this research, reported previously1,2, demonstrate that it is relatively easy to find Varroa-tolerant colonies in managed apiaries, and to use these to produce and maintain Varroa-tolerant strains of honey bees. Our Varroa tolerant population has survived for nearly six years sustaining a low mean annual infestation level constant between 6 and 7 mites per 100 bees. Varroa-tolerant bees are essential for the development of any Integrated Pest Management Program for Varroa. Varroa-tolerance implies that honey bees and beekeepers can live with a low level of Varroa infestation just as they currently live with low level tracheal mite infestations. Varroa-tolerance likely includes a combination of factors pertaining to the biologies of both bees and mites. We did not attempt to identify any Varroa-tolerance factors in our initial studies.

Interest in our approach to producing and maintaining Varroa-tolerant honey bees has led us to encourage other beekeepers to try our strategy. Moreover, the strategy needs to be tested in other localities. Therefore, we have set forth our step-by-step procedures as a recipe that every beekeeper can follow to produce his/her own Varroa-tolerant bees. The only requirements are a working knowledge of honey bee colony management and the ability to rear and naturally mate queens. If one lacks queen-rearing skills, he/she can learn them (it is not that difficult) or team up with a fellow beekeeper who knows how. Increased Varroa-tolerance should be achieved in two years or less and further improved each year thereafter. Remember always keep detailed and complete record on each of your colonies. Success depends on it.

What To Do

1. Identify Varroa-tolerant colonies in your apiaries
Methods for this are described in the next section. Our experience suggests that as few as 3 and as many as 10 percent of colonies in any apiary are somewhat Varroa-tolerant. Beekeepers should be aware that this ratio could vary among geographic regions. Varroa-tolerant colonies go unnoticed when all colonies are treated with Miticides. You will want to begin with at least 10 Varroa-tolerant colonies in all. More are better. Varroa-tolerant colonies are identified, and isolated; you can continue to treat your other colonies until they can be requeened with program stock. Be sure to maintain isolation as described below for your selected stock.

2. Move all colonies identified as Varroa tolerant to single isolated test apiary. This apiary should be at least 3-4 miles from managed colonies treated for mite control.

We lack scientific proof that drones from Varroa-susceptible colonies, which mate with Varroa-tolerant queens, diminish Varroa-tolerance. However, we have maintained strict isolation for mating and believe this isolation to be of paramount importance in the success of our research program

3. Monitor Varroa levels in the selected colonies every 3 months.

There are several ways to do this. See the next section.

4. Graft queens from only those colonies with the lowest mite levels
Eliminate from the test apiary all colonies with more than 15 mites per 100 bees. As the program advances, lower this cutoff limit to 10 mites per 100 bees or less. Never use colonies with known problems such as disease, poor productivity or unacceptable defensive behavior no matter how Varroa-tolerant they may appear

5. Mate all queens in the isolation test apiary
Any traditional mating nuclei will work on this

6. Requeen colonies in your other apiaries as queens become available.
It is best to requeen all colonies in a single apiary at the same time if possible. Once requeened, these colonies become candidates for future selections for improved Varroa-tolerance, hence, the need for good record keeping.

How To Do It

1. Finding Varroa-tolerance
Varroa-tolerant colonies can be identified using one or more of the following techniques.

A) Use survivor colonies. Sometimes colonies or whole apiaries go un-treated unintentionally, or they may have been abandoned

B) Prior to fall treatment with Miticides, look for those colonies with little evidence of mite presence. Use colonies having:
· Good brood patterns
· An absence of worker pupae in uncapped cells
· Few worker brood cells with mite feces in them3
· Few drone brood cells with mites
· An absence of bees with deformed wings
· Few bees seen with mites on them
· Few of dead mites on bottom boards

C) Gladly accept / purchase survivor colonies from beekeepers going out of business if the colonies haven’t been treated for Varroa in the preceding 12 months.

D) As a last resort you can ‘bite the bullet’ and simply elect to withhold mite control measures from one or more apiaries and allow all mite susceptible colonies to die. The survivors can be used as part of the selection pool. Clearly, some beekeepers will find this economically impossible. However, others may find this expedient, especially if they are downsizing.

2. Isolating Colonies
Finding an isolated site 3-4 miles from other treated apiaries may be difficult for some, especially smaller, beekeeping operations. Don’t give up. Isolated sites are out there. In the worst case scenario, if isolated sites can’t be found, simply put queen excluders between the lowest hive body and the bottom board on treated colonies to keep the drones from flying. Don’t worry about feral colonies. If they exist they are probably already Varroa-tolerant

3. Determining Varroa infestation levels
Pour ordinary rubbing alcohol into a small jar (like a baby food jar) until it is half full and replace the lid. In the apiary, open each colony and remove a frame with bees from the brood nest. Being careful to avoid the queen, lightly scrape the open mouth of the jar upwards on the frame. Bees above the jar will fall into it. You will want to capture approximately 100 to 120 bees. Replace the lid and be sure to label both the colony and the jar in a way that you can always and clearly associate the jar with the colony. At home at the kitchen sink gently shake the jar and pour the sample of dead bees and mites into a screen strainer over a large white bowl. Use a faucet spray attachment to thoroughly wash the mites off the bees into the bowl. A strong spray works best. Stop before the bowl overflows and count and record the mites floating on top of the water. Discard the water and repeat the procedure two more times (most if not all mites will be in the first wash). Then, count the number of bees in the sample. Mathematically calculate the number of mites per 100 bees.

4. Grafting and rearing queens
Produce queens from colonies with the lowest mite counts. There are several approaches that can be taken in grafting and rearing queens. Traditional queen rearing methods are presented by Dr’s Laidlaw and Page4. Alternatively, equipment for simplified queen rearing is available from suppliers of beekeeping equipment. As a last resort, simply remove a frame of eggs and young brood from a selected colony and place the frame in a queenless colony with only capped brood. The bees will rear several queens. You will need to harvest the cells or use a push-in cage to isolate the cells a day or two before the first queen emerges and incubate the cells until emergence. The limitations here are the number of queens that can be produced at a time, the difficulty of cutting off the emergency queen cells, and determination of the ages of these queens in anticipation of their emergence times.

We emerge our queens in an inexpensive Styrofoam incubator kept at 94 degrees F. It is available from Miller Manufacturing Co., St. Paul, MN.

5. Queen mating in isolation
Because you have maintained accurate records, and you have obtained your queen cells by grafting, you will know exactly how old your queen pupae are. One to three days before the queens are due to emerge in the incubator, place each cell in a mating by wedging its base into the face of a brood comb or between the top bars of two brood chamber frames within the cluster. Be careful not to damage the cell. The queens will emerge and mate. Alternatively you can allow the queen to emerge in the incubator or place the cell in a screen emergence cage in the colony. If you choose to have the queen emerge in an incubator, place each cell in its own vial so that the queen drops to the bottom when she emerges. Place a small ball of soft sugar candy at the bottom of each vial. The vial makes it easy for you to catch and mark the queen before she mates. Marked queens make it easier for you to follow the progress of your work. Be sure to destroy colony-made cells, if present, before introducing the queen. Care-fully, release her so that she crawls down between the frames. Be careful not to let her fly away as she may be lost. If you allow the queen to emerge in the incubator, you will need to use one of the queen introducing techniques below.

Be sure that your survivor colonies have lots of drones. If drone numbers appear low, you can increase them by placing one or two frames with drone comb or foundation in each of these colonies. (Note: Drone foundation can be purchased from bee supply companies) This must be done in advance of queen rearing and timed so that mature drones are available at the time of queen emergence. Frames with drone combs can be saved and reused, instead of using foundation.

6. Requeening
First, the old queen must be found and killed. Once this is done, the colony may be allowed to remain queenless for 3 days, except when working with bees that carry African honey bee genes. In this latter case queen acceptance will be highest if the new queen is introduced (using a cage) immediately after dequeening.

Mated queens can be installed in colonies by means of one of several techniques4. We prefer candy plug induction cages. First the queen in the mating nook is captured and marked (if not already marked). Then, the queen is placed in the introduction cage, which is wedged between two frames inside the cluster of bees. The worker bees consume the candy blocking the queen’s escape from the cage where upon the queen emerges and soon begins laying eggs. The cage can be removed whenever you next visit the apiary and check for queen acceptance. Alternatively, you can use push-in cages made of 1/8th inch hardware cloth. However, you must remember to come back and remove them in 3-5 days.

Or, you can unite the mating nook with the dequeened/queenless colony using traditional techniques like a newspaper barrier.

Once you have requeened all of your colonies with program queens you may, from time to time, find a colony with unacceptably high levels of Varroa. Simply treat the colony and immediately requeen it with Varroa-tolerant stock.

Summary

We have found that producing Varroa-tolerant honey bees is relatively simple and straight forward. It may not work equally well in your area, but this should be tested. Our concept is based on fundamental biological principals and beekeeping basics. Utilizing locally adapted stock ensures that your colonies will be most prolific and productive. Grafting and rearing of queens may be viewed by some beekeepers as a stumbling block in the production of Varroa-tolerant bees. However, the techniques are not difficult and the work can be personally rewarding to avid beekeepers. If you choose not to rear queens, try collaborating with a beekeeper who knows how. Beekeeping clubs should consider developing Varroa-tolerance projects within their areas. Varroa-tolerance is the first step towards an IPM program for Varroa.

Using queens from our selective breeding program described above, we have requeened virtually all of a 600-colony operation here over the last two years ­ 1998 and 1999. In the fall of 1998, over one-fourth of the operation was not treated with miticide, and there were very few losses directly attributable to Varroa damage. In the fall of 1999, only about one hive in fifteen had significant Varroa damage, and only those were treated. These colonies also have been, or will be, requeened as soon as more queens are available in early 2000. As this is being written (April, 2000) most hives in the operation are brooding well, and showing very little, if any, ill effects from Varroa. This is in spite of the stresses put on the bees by a summer (1999) of very low rainfall and poor plant growth, followed by the driest fall and winter in recorded history.

References

1. Erickson, E.H., Atmowidjojo, A.H. and Hines, L.
Can we produce Varroa-tolerant honey bees in the United States?
Amer. Bee Jour. 828-832. 1998

2. Erickson, E.H., Atmowidjojo, A.H. and Hines, L.
Varroa-tolerant honey bees are a reality.
Amer. Bee Jour. 931-933. 1999

3. Erickson, E.H.
Fecal accumulations deposited by Varroa can be used as a simple
field diagnostic for infestations of this honey bee parasite.
Amer. Bee Jour. 63-64. 1996

4. Laidlaw, H.H. Jr., and Page, R.E. Jr.
Queen rearing and bee breeding.
Wicwas Press, Cheshire, CN. 224 pp. 1997