1. immediately following treatment was counted (Fig. 4), and
average mite drop per minute was calculated.
Evaluation of powdered sugar dusting as a method of suppressing varroa mites
(Varroa destructor) in honey bee (Apis mellifera) colonies
Kim Rawlins and Cory Stanley
References
The varroa mite, Varroa destructor (Fig. 1), the most damaging pest of honey bees (Apis
mellifera) worldwide, was introduced to the U.S. in 19875. Consequently, beekeepers became
reliant on chemical mite treatments to maintain healthy colonies. However, chemical miticides
not only harm mites but can harm honey bees and contaminate hive products. Mites have also
begun to evolve resistance to these chemicals. Therefore, alternative treatments are
necessary4.
A popular non-chemical mite control method that originated in Europe involves dusting
powdered sugar on honey bee colonies6, which is believed to make it difficult for mites to cling
to bees and it also encourages bee grooming, which removes mites1. If the hive is equipped
1. Fakhimzadeh, K. 2000. Effectiveness of confectioner sugar dusting to knock down Varroa destructor from adult honey bees in laboratory trials.
Apidologie 32: 239-148.
2. Fakhimzadeh, K. 2000. Potential of super-fine ground, plain white sugar dusting as an ecological tool for the control of varroasis in the honey bee
(Apis mellifera). Am. Bee J. 140: 487- 491.
3. Huang, Z. 2012. Varroa mite reproductive biology. http://www.extension.org/pages/65450/varroa-mite-reproductive-biology.
4. Macedo P., Wu J & Ellis M. 2002. Using inert dusts to detect and asses Varroa infestation in honey bee colonies. J. Apic. Res. 40: 3-7.
5. Stevanovic J, Stanimirovic Z, Lakic N, Djelic N & Radovic I. 2012. Stimulating effect of sugar dusting on honey bee grooming behavior. Entom. Exp.
143: 23- 30.
6. Yoder, S. 2012. Honey Bee Colony Health. Taylor & Francis Group, Boca Raton, FL.
7. Zar, J. H. 1999. Biostatistical Analysis, 4th Ed. Prentice Hall, Upper Saddle River, NJ.
Methods
• A bee yard was set up in Logan, UT in August 2012 (Fig. 2).
• Hives ranged in size from two to four boxes. Ten control
and 10 treatment hives were assigned. For each control
hive of a particular size, a hive of the same size was also
assigned to the treatment group.
• Treatment colonies were dusted with 1 cup per hive of
Kroger ® powdered sugar four times over six weeks (Fig. 3).
Control colonies were similarly manipulated, but not
dusted. The number of mites that fell off of each colony
Introduction Results
Discussion
Figure 1. Varroa destructor (clockwise from top right), mature
daughter mite, mother mite, two mature males and an immature
(deutonymph) daughter.
Figure 2. The bee yard contained six
groups of four hives each, but only 20 of
the hives were used. In each group of
hives, two were randomly assigned to
the control group, and two were
randomly assigned to the treatment
group.
Figure 5: Replacing Crisco® sheets used
to collect mites.
Figure 4: Counting initial mite drop
immediately following powdered sugar
treatment.
Figure 3: The bottom and second box of each treatment hive were dusted with ½ c
of powdered sugar, which was then brushed over frames. Control hives were
brushed and left standing open for a comparable amount of time,.
with a screened bottom board, mites cannot
return to the colony once they have dropped.
Because of past research, we hypothesized that
dusting of honey bee colonies would significantly
increase the mite drop per hive and therefore
lead to a decrease in overall mite populations.
However, past laboratory-based research differed
from methods typically used by beekeepers. Our
experiment sought to test methods that actual
beekeepers will be able to implement easily. We
also wanted to verify that positive effects from
powdered sugar treatments will be seen under
the climatic conditions of Northern Utah.
Acknowledgements
We would like to thank Martin James for providing hives and setting up the bee yard. We are grateful to Merril
Longmore, Clark Evans, Ivy Pitts, Martin James, and Lauren Miller for helping with treatments and mite counts.
We are very appreciative of a Utah State University Cooperative Extension grant which funded this research.
A significantly larger number of mites dropped off of treated colonies immediately
following powdered sugar dusting than fell off of control colonies that were manipulated
without powdered sugar. These results greatly support our hypothesis that powdered
sugar treatments increase mite drop compared to colonies left untreated. In addition,
the ongoing average mite drop per day was smaller for treated colonies than for control
colonies, implying that colonies treated with powdered sugar had smaller mite
populations following treatments. This also supports our hypothesis that powdered
sugar treatments lead to an overall decrease in mite population.
If conducted again, a better design of a Crisco® sheet that could simply slide in and out of
a screened bottom board would simplify the entire process, and would be more similar
to the process a hobby beekeeper would use. It would also be interesting to test this
treatment during different seasons to see if there is an ideal period of time to treat.
These results will be of great importance to beekeepers in Utah. While seeking safe,
effective methods of controlling varroa mite populations, beekeepers will be able to
implement these simple powdered sugar dustings without the worry of harming their
colonies or their products. Our results clearly show that powdered sugar dusting does
suppress varroa mite populations in Northern Utah honey bee colonies.• Screened bottom boards were placed underneath each hive. Sheets of paper
smeared with ~2 mm of Crisco® vegetable shortening were placed beneath bottom
boards of all hives to collect mites as they dropped.
• Crisco® sheets were collected and replaced five times over six weeks (Fig. 5). The
number of mites per sheet were counted, and average mite drop per day was
calculated.
• Multiple linear regression was used to determine if
time (sample number), hive size, and hive position
influenced the number of mites dropped per minute
immediately following treatments as well as the number
of mites dropped per day (Sigmaplot 11). F-tests
compared regression equations for control and
treatment groups7.
Huang, 2012
Multiple linear regression showed
that time (sample number) and hive
size affected the cube root
transformed average number of
mites that dropped per minute
immediately following powdered
sugar dusting for treatment, but not
control, colonies. The square root
transformed average number of
mites dropped per day for control
colonies was affected by both time
(sample number) and hive size, but
treatment colonies were only
affected by time (sample number)
(Fig. 6). Hive position did not have
an effect on treatment or control
colonies.
Figure 6. Multiple regression models of factors affecting cube root of
average number of mites dropped per minute for (a) powdered sugar
treated and (b) control colonies, and square root of average number of
mites dropped per day for (c) powdered sugar treated and (d) control
colonies. In equations, xs corresponds to sample number, and xh
corresponds to hive size.
y = -0.161 + 0.252xs + 0.379xh
R2
a = 0.340, P < 0.001 a
y = 0.0289 + 0.00913xs – 0.00291xh
R2
a = 0.000, P = 0.826 b
y = 1.220 + 0.490xs + 0.364xh
R2
a = 0.340, P < 0.001 c
y = 5.263 + 0.470xs - 0.959xh
R2
a = 0.262, P < 0.001 d
Comparison of treatment and control groups’ regression equations showed that
powdered sugar treated colonies had significantly more mites drop immediately
following treatments than did control colonies (F0.05(1), 3, 94 = 140.42, P < 0.0005).
Also, treated colonies had significantly fewer mites drop per day than did control
colonies (F0.05(1), 3, 114 = 3.11, P < 0.05).