8963~

Sterilization of honey for bee feeding

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by JONATHAN W. WHl't'E, sr.
Eastern Regional Research Laboratory', •.hiladelphia 18, Pennsylvania
and A. p, STURTEVANT'
Entomology Researcll Branch Agricultural Research Service
United States Department of Agriculture, Laramie, Wyoming
ROM MANY POINTS of vie w, touowed the following instructions
Fhoney appears to be an ideal material (2); "No attempt shouid be made to
for the various types of bee feeding. recover honey from diseased colonies
A disadvantage, of course, is the higher unless there is a distinct economic
cost of honey over sugar, which is saving. Since it is often impossible to
widely used. Off-grade, dark, strong- ascenain the source of honey pur-
flavored, unmarketable honey would chased on the open market, such honey
be economically more suited for the SHOUldnot be ted to COlonies of bees
purpose. Unfortunately, such use of if It can be avoided. If such honey
honey is often not recommended be- has to be used, it should first be diluted
cause of the possibility of spreading with an equal volume of water and
the serious bee disease, American foul- boned tor an hour in a closed vessel."
brood. Burnsrde recommended in 1945 (3)
Several years ago, at the request of that "boiling for 30 minutes can be
Production and Marketing officials of depended upon to destroy the virulence
this Department, we undertook a study of spores of Bacillus larvae under any
of this problem. The objective was the ordinary conditions." This was based
development of a practical method for 011 a thermal resistance study of spores
the sterilization of honey with respect of B. larvae in water, diluted honey
to the organism causing American and beeswax. Sixty-two colonies of
foulbrood so that the then considerable bees received honey containing spores
amounts of low-grade honey in the that had been boiled for various times
hands of the Department might be from five minutes to five hours. None
used for bee feeding without possible showed any signs of disease during the
spread of disease. J. I. Hambleton, of season. All spores that had been boil-
the Section of Bee Culture and Biolog- ed in honey showed vegetative growth
ical Control, urged that sulfa not be in the laboratory; all, however, also
relied on for the purpose and also that showed a delayed germination time.
the treatment be such that the spores Burnside (3) interpreted the loss of
of the organism be killed and not simp- virulence as brought about by the in-
ly be rendered nonvirulent. crease in germination time of the
_, There was some previous experience heated spores beyond the 2¥1 day peri-
'w to go on. White in 1920 (1) stated od in which larvae are susceptible to
the disease, according to Woodrow (4).
that a variation had been observed in
the thermal resistance of spores of With these requirements in mind,
BaciUus larvae obtained from different we. have worked out a p~ocess by
geographical sources. He found that which honey can be sterilized with
the most resistant spores studied, when respect to AFB spores. In this work
suspended in water, were destroyed by we used honey infected with B. larvae
heating at 212" F. for 11 minutes but spores at a level recommended by
withstood ,longer heating when sus- other workers in the field, about 150
pended in honey or diluted honey. million per ml.
White found that spores suspended in Approaching the Problem
honey diluted with an equal volume OUR FIRST APPROACH to the
of water could be destroyed by heat problem was to try to find some
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at 212 F. but that it might require chemical agent or material that we
half an hour or more. could add to the honey that would kill
Many beekeepers for a considerable the spores, either alone or in combina-
number of years have more or less tion with some heating. After many
1 A laboratory of the Eastern Utilization
Research Branch. Agricultural Research tnals, we found several substances
Service, U.S. Department of Agriculture. that looked promising at a level of
• In cooperation with the University of 0.1 %., combined with heating. Sam-
Wyoming. a These are listed on page 13 of reference 5
Purchased by
Agricultural Research Service
U. S. Department of Agriculture
For Official Use
 ples were made up and tested by feed- was to use the other end of our time-
ing to honey bees. The chemicals were temperature curve. Instead of high
fair sporicides, but they also killed the temperature-short time, we used lower
bees. temperature-longer time. In order to
After this experience, we did some eliminate costly equipment, we used _
fundamental res ear chon the AFB the boiling point of honey when diluted •••.
spores. We decided to rely on heat to about 55% solids. From the ther-
alone and carried out what is called mal-death-time curve, for the tempera-
a thermal-death-time study on the or- ture of 220' F., which is the boiling
ganism. This means that we determined point at our altitude (about 500 feet
in the laboratory just how high a tem- above sea level) we found that the
perature was necessary and how long time required for sterilization, includ-
it had to be applied to kill the spores. ing a safety factor, is 90 minutes. This
This is the sort of study that our com- time would be increased with lower
mercial fruit and vegetable canners use boiling points at higher elevations, as
in determining the heat processing of shown at the end of this article.
canned foods. Some of our darker, off-grade hon-
After the time-temperature relation eys throw down a precipitate when
had been d e t e r min e d for B. larvae they are boiled. This can be avoided
spores, it was possible to obtain from if a small amount of phosphoric acid
the data the time of heating needed to (an edible food acid) is added.
kill the spores at any temperature. A We prepared a quantity of honey
description of the determination of the carrying about 150 billion spores per
thermal-death-time .c u r v e has been WeI, diluted it to 55% solids, acidified
published elsewhere (5). Thus we had it with one fluid ounce of phosphoric
the type of information on which a acid (diluted 1 to 5 with water) per
process could be based. gallon of honey and boiled it for 90
We then developed a process, and minutes. The temperature increased
our Engineering Section modified ex- from 218' to 227' F. during this time.
isting equipment so that it could be Laboratory culture tests showed that
used for a continuous sterilization there was no growth of B. larvae over
process for honey. Using a high-tem- a 30-day incubation period. Then it
perature short-time approach, we could was submitted to thG Bee Culture and
kill the spores by heating the diluted Biological Control Laboratory at Lara-
honey' to 284' F. in two seconds, mie, W yom i n g, along with some
holding it at that temperature for 50 unheated infected control honey for
seconds, and then immediately cooling feeding tests.
it to the boiling point of about 220'. Colony Feeding Tests ••
In the small pilot-plant equipment, we
could treat the diluted honey at a rate
of 20 gallons per hour. Incidentally,
T HE FIRST colony feeding tests were •.
started the latter part of May and
this treatment had virtually no dam- early June 1952. Three healthy over-
aging effect on the honey (5). Honey wintered colonies of uniform strength
treated in this manner, as well as simi- were chosen. A careful inspection at
lar untreated honey, was non-toxic that time showed no active disease or
when fed to bees in cages. old disease scales. Two of the colonies
There is a catch to this process. In were fed approximately two quarts
order to make it economically reason- each of the treated honey on two days
able, the equipment has to be designed a week apart, a total of four quarts.
to treat several mill ion pounds of The third colony, used as a check, was
honey per year. Of course, there isn't fed two quarts of the spore-containing
that amount of such honey at one han e y that had received no heat
place, and it isn't practical to ship treatment.
honey for the purpose. It isn't the sort The check colony had developed
of thing a beekeeper could set up in considerable AFB by the 19th day
the honey house. after being fed the untreated honey,
Our final approach to the problem and near the end of June was heavily
diseased. Disease developed in both
4 Honey was diluted to 55% solids; two
parts by weight of honey to one part test colonies fed the treated honey.
of water. Six diseased cells appeared in one
 colony by the 19th day after being fed ny or introduced from th~ ol:ltside
the treated honey. In the other colony might eventually produce active infec-
disease developed much more slowly; non in a few larvae, from which the
only two AFB cells had aPI',eared by disease COUldspread through the colo-
~ the forty-fifth day after the first feed- rues, as apparently appeared to be the
Wing. case.
Throughout July, disease s pre ad The treated honey tests made in
very slowly in both colonies, only 1952 were con sid ere d unreliable,
from two to five cells of AFB were since they were not sufficiently con-
seen at anyone inspection. After the trolled to prevent the possibility of
first of August until near the end of disease from sources other than the
brood rearing in September, however, treated honey. Therefore, a second lot
both colonies became relatively heavi- of AFB honey was prepared early in
ly infected. Since these colonies all 1953 and sent to Laramie for further
were headed by queens of the same colony testing; the heating procedure
relatively susceptible stock, the event- and the B. larvae spore content were
ual spread of disease in each colony, the same as used in 1952. In 1953,
after the development of the slight however, extra precautions were taken
amount of initial infection, was to be to prevent any contact of the bees with
expected. any source of infection other than what
There are some explanations for the might be present in the treated honey
way disease developed in the two test fed to the colonies. The laboratory
colonies fed the treated honey. It is culture tests' were negative for growth
possible, although not probable, that a of B. larvae.
sufficient number of spores to produce
the slight initial infections may have ",EVEN COLONIES were established
escaped the lethal conditions, either LJ for this purpose about the middle
by adhering to the sides of the vessel of May 1953 with two-pound packages
above the liquid surface or in foam of bees and sister queens, shipped from
produced by the boiling, thereby re- Louisiana. They were fed at the start
maining both viable and virulent. How- only sugar syrup (one to one by vol-
ever, the sides of the vessel had been ume of sugar and water), and each
washed down several times. was given one pollen cake (pollen f~om
Since the laboratory culture tests a known non-infected source, mixed
showed no growth of B. larvae even with soybean flour). After the colonies
after 30-days' incubation, there is the had developed to sufficient strength,
more probable possibility that those six were moved to a completely isolated

e test colonies may have picked up infec-

tion from some previous or outside
source other than from the heated
honey fed to them. The test colonies,
location some 15 miles from any dis-
ease-experiment apiaries or any other
known source of AFB infection. The
seventh colony was held at the original
although apparently healthy at the apiary location.
time they were fed the heated honey, The six isolated test colonies were
may have carried over a small hidden each fed two quarts of the 1953 heat-
focus of infection from B. larvae treated honey on July 1, and the
inoculations in connection with the seventh colony, used as a check, was
American fouJbrood resistance studies fed two quarts of unheated honey on
in previous years. An occasional case the same date. Some disease appeared
of disease the sec 0 n d season after in the check colony by July 10 and by
inoculation has at times been observed July 21, three weeks after being fed
in colonies with a similar history. the untreated honey, it was heavily
Furthermore these colonies were lo- diseased with Arne ric an foulbrood.
cated in an apiary in which some other Inspections of the colonies fed the
AFB experimentally diseased colonies heat-treated honey were made about
were present. The test colonies could every 10 days throughout the 1953
have picked up infection either from season until the end of brood rearing.
drifting nurse bees or through robbing. No disease was observed in any of
Since the test colonies were headed these test colonies. All colonies .con-
by AFB susceptible stock queens, a 5 Procedures for these tests are given in
slight amount of infection in the colo- reference 5.
 sumed the heated honey about as lowing process by which honey can
readily as sugar syrup, and no visible be treated to permit feeding to bees
evidence of harmful effects to the without fear of spreading American
brood or to the adult bees could be foulbrood.
observed. All but one of the test colo- Diluted phosphoric acid (17%): To _
nies came through the winter of 1953 make, mix one part concentrated (85%) _
to 1954 in good condition. One colony orthophosphoric acid with four parts
died during the late winter from star- of water.
vation. None of the remaining colonies Mix one 60-pound can of honey
showed any evidence of AFB when with 30 pounds of water (about 31;2
inspected on April 18 and again on gal.), add five fluid ounces of diluted
June 3, 1954. phosphoric acid and heat to boiling.
Therefore, res u Its of one entire Note the temperature at which active
active season and observations well into boiling begins and continue boiling for
the second season indicate that honey the time given below.
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which may be contaminated with spores 215 F.

0
2V<!hours
of B. larvae or honey from unknown 220 F.
0
11;2 hours
sources, can be made safe for feeding 225 F. 1 hour
to healthy colonies by the heat treat- If much foam is formed, it should be
ment described above. Colonies fed skimmed off and disposed of, since
such treated honey should be kept spores could possibly survive the heat-
under careful observation for more ing if they remain in a surface foam.
than one year. .Such boiled honey Acknowledgements
should not be fed in winter because of We are indebted to Eleanor J. Cales-
the possible danger of its causing dys- nick and Joseph Naghski for bacterio-
entery. Feeding such honey should be logical work and to A. S. Michael,
carried out only after bees can have Floyd Moeller and J. D. Hitchcock for
unimpeded flights in the spring. toxicity testing, and also to J. D. Hitch-
cock and I. L. Revell for assistance in
Process for Treating A.F.B. Honey colon y manipulations and disease
We can therefore outline the fol- inspection.
REFERENCES
1. White, G. F. 1920. American foulbrood. U.SD.A. Bulletin No. 809. 46pp. i11us.
2. Hambleton, Jas. I. 1933. The treatment of American foulbrood. U.S.D.A. Farmers'
Bulletin No. 1713. 13 pp. i11us.
3. Burnside, C. E. 1945. Transmission of American foulbrood by heated spores of BacU-
lUISlarvae and their growth in culture. Jour. Econ. Ent. 38 (3): 365-8.
4. Wood':Ow, A. W. 1941. SusooptibUity of honey bee larvae to American foulbrood.
Gleanmgs in Bee Culture 69 (3): 148-151 and 190.
5. Calesni~k, E. J .. and White, J. W., Jr.
spores m honey.
1952. Thermal resistance of Bacillus larvae
Jour. Bact. 64 (1): 9-15.
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Reprinted from Gleanings in Bee Culture, November 1954. Vol. 82, No. 11, Pages 658-661.