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The Minnesota Hygiene Queen |
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The hygiene queen
was written by Marla Spivak & Gary Reuter. Marla is
Associate Professor and Extension Entomologist, University of
Minnesota and Gary is a Research Technician at the
same University.
Introduction
Hygienic behavior of honey bees is the primary natural defence
against American foul brood (Park et al., 1937; Woodrow and Holst,
1942; Rothenbuhler, 1964) and chalk brood (Gilliam et al., 1983).
Hygienic bees detect, uncap, and remove diseased brood from the combs
before the disease becomes infectious.
Hygienic behavior also is one defense against Varroa mites
(Peng et al., 1987), and although it is not the main mechanism of
resistance to the mites (Harbo and Hoopingarner, 1997), it appears
to limit their reproduction and population growth to some degree.
Our studies have shown that it is possible to select for hygienic
behavior without compromising honey production or gentleness
(Spivak, 1996; Spivak and Reuter, to be published). The trait can be
found in approximately 10 percent of the managed colonies found in
the United States, in any race or stock of bees. We feel it would
benefit the beekeeping industry to have hygienic lines of bees
commercially available.
In this article, we present a simple way of screening
colonies for hygienic behavior. We also discuss some frequently
asked questions about the behavior, and how to breed hygienic colonies.
Using Liquid Nitrogen
For years, we screened colonies for hygienic behavior by
cutting out a section of comb (2 x 2.5 inches) containing sealed
brood, freezing it for 24 hours, then placing the frozen comb
section in the colony to be tested. If the test colony was hygienic,
the bees would uncap and remove the freeze-killed brood within 48
hours. When tested repeatedly (Taber, 1982; Spivak and Downey, 1998).
Cutting comb sections out of frames is relatively messy and damages
the combs, so we sought a better way of killing brood without having
to handle the combs.
Dr. Jerry Bromenshenk at the University of Montana was the
first to suggest using liquid nitrogen (N2) to freeze a
section of sealed brood within the frame. He found that freezing the
brood this way was more efficient than cutting, freezing, and
replacing comb inserts. Based on his suggestions, we conducted several
tests to determine how much liquid N2 was necessary to
completely kill the brood, and whether the test yielded the same
results as cutting and freezing comb sections. We are now convinced
that freezing brood with liquid N2 is the best screening
procedure found to date for assaying hygienic behavior.
Liquid N2 is relatively inexpensive and easy to
obtain; check with your local veterinary practice or livestock
artificial inseminating firm. It must be kept in an appropriate tank
and securely fastened to the truck during travel to avoid spillage.
Common sense and several precautions must be used when
handling liquid nitrogen. It has a boiling temperature of -195
degrees C (-320 degrees F) which means that it is extremely cold
and will kill skin (causing severe frostbite) on contact. Protective
clothing including heavy gloves, boots, a face shield and safety
glasses should be worn. The boots should be sufficiently secure
so that the liquid N2 cannot be spilled into them.
You will need to construct (or find) a hollow cylinder
into which you will pour the liquid N2 to freeze a circular
section of sealed brood. We have been using a 3-inch (75 mm)
diameter cylinder, cut from galvanized clothes-dryer vent. The
cylinder must be at least 100 mm long because the nitrogen will
boil on contact with the brood. The thinner the walls of the cylinder,
the easier it is to press into the comb assuring a good seal.
250-300 ml of liquid N2 is needed to freeze-kill
all the brood (approximately 160 cells) within a 3-inch diameter
cylinder. A smaller amount will not kill all of the brood, leading to
erroneous results. Use a 300 ml or larger expanded polystyrene
foam coffee machine cup for measuring and pouring. Other materials
will shatter on contact with the liquid N2.
Select a frame with at least a 3-inch diameter circle
of sealed brood containing fewer than 30 unsealed cells within the
circle. Lay the frame horizontally across a support (i.e. an empty
super). Twist the metal cylinder into the sealed brood until it
reaches the midrib. Record the number of unsealed cells inside the
cylinder. Pour a 50-60 ml of the liquid N2 into the
cylinder and wait for it to freeze the edges or evaporate. Then pour
the remainder of the liquid N2 into the cylinder. Wait to
remove the cylinder until it thaws, which may take three to five
minutes. If you have additional cylinders, you can start the next test
while you are waiting for previous ones to thaw. We put a drawing pin
(thumbtack) in the top of the frame to mark the frame and the location
of the test on the frame. Some hygienic colonies clean and repair the
comb so quickly that it is hard to locate the test when you return.
Place the frame in the center of the brood nest.
Remove the frame containing the frozen brood 48 hours
later, and record the number of sealed cells remaining within the
circle. When testing a colony that has been requeened, six to eight
weeks must elapse after requeening for the bees in the colony to be
daughters of the new queen.
Frequently Asked Questions
Often we are asked if hygienic colonies tend to have clean
bottom boards, or if they tend to remove debris (such as wax paper,
newspaper or cardboard) from the colony more quickly than other
colonies. Mayer (1996) suggested that if colonies eat grease patties
quickly, they might be hygienic. Removing debris from the hive is a
form of cleanliness, but it is not necessarily a sign that the bees
carry the hygienic trait.
Although the common usage of the word hygienic denotes
cleanliness, hygienic behavior is a specific response by the bees to
diseased and parasitized brood. A colony that keeps its hive clean
does not imply that it will be resistant to diseases. Colonies must
be screened for hygienic behavior using an assay such as the one
described above. If a colony removes all of the freeze-killed brood
within 48 hours, the colony will probably be resistant to
diseases and will tend to remove mite-infested pupae. To determine
whether they can actually resist the diseases or mites, the colony
would have to be challenged with American foulbrood, chalkbrood or
mites.
Another question we encounter concerns the difference
between hygienic and grooming behaviors. Grooming behavior involves
an interaction between adult bees; one bee removes mites or debris
from the body of another bee. Alternatively, a bee may groom herself.
Grooming and hygienic behaviors are different traits, and selecting
for one does not imply selection for the other.
It is assumed by some beekeepers that hygienic behavior is
associated with a high degree of defensive (stinging) behavior. This
assumption stems from the reputation of the Brown line of hygienic
bees studied by Rothenbuhler. Rothenbuhler (1964) showed that stinging
behavior and hygienic behavior are inherited separately. Our
experience has shown that hygienic colonies are as gentle as the stock
from which they were bred.
Propagating Hygienic Colonies
Any race or line of bees
can be bred for hygienic behavior. We recommend that bee breeders
select for hygienic behavior from among their best breeder colonies;
i.e., from those that have proven to be productive, gentle, and that
display all the characteristics desired by the breeder. A breeder can
get a head start on selecting for hygienic behavior simply by rearing
queens from colonies that do not have chalkbrood.
When colonies are first screened for hygienic behavior using
liquid N2, they may not remove all of the frozen brood
within 48 hours. The colonies that remove the most freeze-killed
brood within 48 hours should be propagated by rearing queens from
them. Subsequent generations will remove the brood more quickly,
because hygienic queens from the first generation will produce drones
for the second generation. If the hygienic queens are instrumentally
inseminated with semen collected from drones from hygienic colonies,
or are mated naturally in an isolated area, where all the surrounding
drones are from hygienic colonies, it will be easier to fix the trait
in your line of bees.
Beekeepers should rear queens from unrelated hygienic
colonies each year to avoid the negative effects of in-breeding. In
time, if many bee breeders select for hygienic behavior, the frequency
of the trait should increase in the general population of bees, which
will increase the chances that any queen will encounter drones that
carry the trait.
The effects of American foulbrood, chalkbrood and Varroa
mites can be alleviated if queen producers select for hygienic
behavior from their own lines of bees. Because a small percentage of
the managed colonies today express hygienic behavior, it is important
for many bee breeders to select for the behavior to maintain genetic
variability within and among bee lines.
Our experience has shown there are no apparent negative
characteristics that accompany the trait. Years of research
experience have shown it would greatly benefit the beekeeping
industry if productive, hygienic lines were available commercially.
References
Gilliam, M., S. Taber III and G. V. Richardson. Hygienic behavior of honey bees
in relation to chalkbrood disease. Apidologie 14: 29-39. 1983.
Harbo, J.R., Hoopingarner, R.A. Honey bees (Hymenoptera: Apidae) in the United
States that express resistance to Varroa jacobsoni (Mesostigmata: Varroidae). J.
Econ. Ent. 90: 893-898. 1997.
Mayer, M. Testing for super hygienic bees. Bee Culture 124: 517-519. 1996.
Park, O.W., Pellett, F.C., Paddock, F.B. Disease resistance and American
foulbrood. Amer. Bee J. 77: 20-25. 1937.
Peng, Y.S., Fang, Y., Xu, S., Ge, L., Nasr, M.E. Response of foster Asian Honey
bee (Apis cerana Fabr.) colonies to the brood of European honey bee (Apis
mellifera L.) infested with parasitic mite Varroa jacobsoni Oudemanns. J.
Invertebr. Pathol. 49: 259-264 1987.
Rothenbuhler, W.C. Behaviour genetics of nest cleaning in honey bees. IV.
Responses of F1 and back cross generations to disease-killed brood. Am. Zool. 4:
111-123. 1964.
Spivak, M. Honey bee hygienic behavior and defense against Varroa jacobsoni.
Apidologie 27: 245-260. 1996.
Spivak, M., Downey, D. Field Assays for Hygienic Behavior in Honey Bees (Apidae:
Hymenoptera). J. Econ. Entomol. 91(1): In press. 1998.
Spivak, M., Reuter, G.A. In press. Performance of Hygienic Colonies in a
Commercial Apiary. Apidologie.
Taber, S. III. 1982. Determining resistance to brood diseases. Am. Bee J. 122:
422-425. 1982.
Woodrow, A.W., Holst, E.C. 1942. The mechanism of colony resistance to American
foulbrood. J. Econ. Entomol. 35(3): 327-330.
Original text by Marla Spivak... This page generated... 07 October 2000
Revised... 18 January & 19 November 2002
