Producing Varroa-tolerant Honey Bees from Locally Adapted Stock: A Recipe*
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
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 bee-keeping 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 pro-duce 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.
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
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.
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