Midnite Bee-Beekeeper's: Reports
A Rapid Field & Laboratory Method to Detect Varroa jacobsoni in the Honey
Bee (apis mellifera)
by KAMRAN FAKHIMZADEH*
*Department of Applied Zoology
P.O. Box 27(Viikki C)
SF-00014 University of Finland
Tel: +358-9-19158393 or +358-40-5536791 GSM
Revised manuscript received for publication March, 2000
The most serious disease in apiculture is varroasis caused by the
mite Varroa jacobsoni Oudemans. Immediate diagnosis of varroasis
is not possible, especially in spring time when bee colonies are
purchased. A new method was developed to detect ecto- and
endoparasites of honey bees focussing on the varroa mite (n=129
separate examinations). The method incorporates washing and
centrifugal force to separate mites from bees in a closed container.
Four rotational speeds: 6342, 5718, 5076 and 4752 rpm, were
tested, for 10, 30 and 60 seconds, with two concentrations of
detergent solution. Both live and frozen bees were examined. The
high detergent level as well as the highest speed were significantly
better (p<0.05) than the low detergent and lower speeds
respectively. The duration of the centrifugation is not critical. The
qualitative detection efficiency (detection % of all infested samples)
of the method is 100% (n- 93) when the infestation level is >3
mites/100 bees, and at 1 mite/100 bees the efficiency is >85% (i.e.
13 positive detection out of 15 samples). The quantitative detection
efficiency (% of mite individuals detected in a sample) of the
method under optimum conditions is >90% when the infestation
level is >3 mites/100 bees. The detection rate when using frozen
bees was significantly better (p<0.05) than when live bees were
Oudemans is an external parasitic mite of honey bees. It was first described
in Apis cerana, in Java (Oudemans 1904). The problem started when beekeepers
transported Apis mellifera to Asia (Goncalves et a1.1985). Today varroa
is found world wide, with some exceptions (Bradbear 1988, De Jong 1990). The
mites attach to the adult bee between the abdominal segments or between body
regions (head, thorax, abdomen) and are therefore difficult to detect (Ritter
1981, Shimanuki and Knox 1991). Generally, varroa remains undetected
up to three or four years
after a hive first becomes infested. Clinical symptoms become apparent when
several thousand mites are present in a colony (Ritter 1981, Robaux 1988).
diagnosis method is to shake bees in a liquid using a rotary shaker for 30 minutes.
Various recommendations have been made for using different liquids, such as
hot water (25deg;,40deg;,60deg; and 100deg;C) (De Jong et a1.1982), 96% ethanol
(De Jong and Goncalves 1981) 70% alcohol (ethyl or isopropyl) (USDA 1987) 25%
alcohol (De Jong et a1.1982) detergent solution, hexane, gasoline or diesel
fuel (De Jong et a1.1982, USDA 1987).
the field methods to detect the mite is to uncap the brood cells and remove
the pupae with forceps, a sharp knife or capping scratcher (De long 1979, USDA
1987, Szabo 1989). Throughout the year, the ether-roll method is used in the
quick field diagnosis of varroa. Some 450-1000 live bees are collected into
a wide mouth jar (Ellis et a1.1988, Herbert et al. 1989, USDA 1987, Gruszka
1988) by using a short burst of ether. The bees are then rotated in a jar for
a few seconds and the mites adhere to the surface of the jar. The average detection
efficiency of ether roll is 35% quantitatively (individual mites detected in
a sample) (Herbert et a1.1989). and 12.5% qualitatively (detection rate of all
infested samples) (Ellis et al.1988). However, the latter value would have been
much higher in a survey with higher infestation levels. Since smoke is used
in the apiary, the high flammability of ether is a safety concern when using
the ether roll method.
is a tedious process and is not possible in the absence of a capped brood (Herbert
et a1.1989). When colonies are sold in spring, beekeepers and apiary inspectors
need an accurate technique for the rapid detection of varroa. The decline of
colony population affects the practicality of taking brood and/or substantial
adult bee samples for ether rolling. The main objective of these studies was
to develop a highly efficient method of detecting varroa mite on a small sample
(100-150) of adult bees. Another objective was to determine the practicality
under field conditions.
1. The Langstroth comb behind the prototype device is for the size comparison.
A new device
has been designed and developed over four years by the Department of Applied
Zoology of the University of Helsinki. The prototype device was built in Finland
by Farmcomp Ltd. (figure 1). Varroa mite detection research was conducted at
the Agriculture Research Centre in Jokioinen, Finland. The device was tested
in the U.S.A. for the detection of Acarapis woodi, in cooperation with
the U.S. Department of Agriculture, Iowa State University and Dadant and Sons
Inc. However, the detection method for the internal mite is still under investigation
and is out of the scope of this article.
incorporates centrifugal force to dissociate varroa mites from bees in a closed
container. Bees and a shaking solution were placed in a rotating chamber. Attention
was given to the consistency of the load (bees and liquid) during experimentation
to have a steady rotational speed. consequently a constant centifugal force.
Four rotational speeds (6342, 5718, 5076 and 4752 rpm.) were examined for 10,
30 and 60 seconds. In a preliminary research the cheapest and most efficient
liquid was found to be a solution of detergent which has no hazardous side effects.
Washing detergent (Leijona) and water was used. Adding the detergent to a container
of water avoids unwanted foam. No annoying foam was formed during the analysis
of the samples. Two concentrations of detergent solution were investigated:
low (one ml in three liters ) and high (one ml in one liter).
Bees were sampled from two
apiaries in Partalansaari, southeastern Finland. A pair of samples (each 0.5
deciliter mean 117 bees) were collected from 36 bee colonies every three weeks
Figure 2. The inner
structure of the closed rotational chamber.
May to August. Equal numbers
of colonies of Apis mellifera mellifera, A. mellifera carnica and A.
mellifera ligustica were used in this investigation. Collected bee samples
were divided randomly into two groups for live (117+;23x+SD range
61-171) and frozen bee (118+25 range 60- 165) analysis. Bees were shaken
from a comb into a container; then 0.5 dl of bees were measured and placed in
a plastic bag. The live bee samples were analyzed within fifteen minutes. At
the end of the day the bee samples were carried to a laboratory and frozen at
approximately -20degC. The samples were defrosted at room temperature prior
A bee chamber within the
rotational chamber consisted of pillars, 3 mm apart, to filter the bees (figure
2). The solution of water and detergent, without bees, (150 ml) was measured
by the use of the rotational chamber and poured into the plastic bag, over a
sample of bees (frozen or live). The solution and bees were then poured back
into the rotational chamber and deposited into the centrifugal device. The remaining
mites, if any in the bag, were also added to the chamber with a paint brush.
By having a wet cluster of bees it becomes easier to place them into the rotational
chamber. Research demands accuracy, however in practice bees can be brushed
directly into the chamber. The motor for rotating the sample can be run by an
automobile 12 volt battery. After centrifuging the cylinder at various rotational
speeds and times, mites were counted on the bottom of the transparent rotational
chamber and bees were removed. The removed bees were placed in a rotary shaker
for 30 minutes in 70% ethanol (USDA 1987), a method which removes 100% of the
mites (De Jong et a1.1982). The bees and any fallen mites were then washed under
a shower of tap water over 2 sieve screens (3mm and 0.5mm in pore-size) for
2-3 minutes (Fakhimzadeh 1993). The mites and the bees were then counted (n=129
Experimental design and
Experiment 1. The
effect of concentration of the detergent solutions
2 (3) factorial design with fixed effects of detergent concentration (low and
high), speed 6342 and 5718 rpm for 30 and 60 seconds. Two levels of each factor
were chosen based on previous experiments giving a total of 8 treatment combinations.
Samples of live bees n= 26 (0.5d1= 100.6+;12.3x+SD ranging 76-120
bees) were randomly assigned to each treatment and inspected for mites blindly
(the examiner not knowing the history of a sample), 4-6 replications were used.
The bees were infested with 13.9+;14.1x+;SD ranging 0.9-49.6 mites
per hundred bees and 8 samples had < 3% mite infestation.
The use of frozen bees vs. live bees
This was also a factorial
design with fixed effects. The factors were freezing/not freezing, speeds 5718,
5076 and 4752 rpm and times 10, 30 and 60 seconds, giving a total of 18 treatments
(n=103 out of which 28 samples had <3% infestation). The low concentration
of the detergent solution was used. Randomization and inspection of the samples
were as in experiment 1. The analyses of both experiments were accomplished
with SAS (Statistical Associates Software) General Linear Modelling (GLM-procedure).
Both experiments were conducted simultaneously.
The effects of detergent
and speed in experiment 1 were both significant (p=0.026 and p=0.005, respectively).
In experiment 2, where different speeds were used, none of the effects were
significant (n=103). However, the effect of freezing was further analyzed by
excluding samples with low infestation levels (< 3.0%) (19 from 69 live samples
and 9 from 34 frozen samples). A significant difference (p<0.05) was detected
in favour of frozen bees. The live bees (n= 69) were infested with x+SD
8.7+8.4 range (0.7 to 38.2) mites per hundred bees. Frozen bees n=34
3: The quantitative
detection efficiency based on experiment 2 (n=100 separate examinations). Frozen
bees, live bees and combined data are shown by an angle, circle and dash, respectively.
Categorical number of observations of infestations <5 to >40 were 43,
24,13, 9, 3, 5, 3, respectively. Notice that the optimum speed (6342 rpm) and
high concentration of detergent solution were not used in this experiment.
4. The qualitative detection efficiency based on both experiments
(n=65 separate examinations) The categorical observations were 15, 13, 13, 11,
8, 5, respectively.
5. The effect of detergent concentration on the mite detection (quantitative).
Means+SE. N=12 in each concentration.
The effect of freezing the bees on the mite detection (quantitative). Means+
SE. N=50 for live
bees, 25 for frozen bees.
7. The effect of freezing the bees on the mite detection (quantitive).
SE. N=50 for live bees, 25
for frozen bees.
with ztSD 15124.8 range
(0.7- 105.1) mites per hundred bees. The quantitative detection efficiency of
the method is >90% (i.e. over 90% of mites in the sample are detected) when
optimal conditions are in use (figures 3, 5 and 6). The qualitative detection
efficiency of the method is 100% when infestation level is >3 mites/100 bees
(n=93), at 51 mite /100 bees the efficiency is >85% (figure 4).The effects
of single factors are displayed in figures 5 to 7.
of detergent concentration is quite clear (figure 5) and becomes obvious considering
the washing and centrifuging mechanisms that are utilized.
significantly different only in experiment 1 since in experiment 2 only the
lower speeds were used. In fact, 6342 rpm seems to differ from 5718, 5076 and
4752 rpm (figure 6).
seemed to have no effect but this was in fact due to the large variation; it
rose mainly from low infestation samples and could be minimized by excluding
samples of <3% infestation level. Again a logical explanation to the freezing
effect can be found that freezing at -20 C may dislodge the mites in the period
before actual freezing occurs (figure 7).
of centrifugation is not critical; even 10 seconds of rotation seems to be enough
especially when optimal levels of other factors are chosen. The maximum velocity,
causing the highest centrifugal force, was obtained in less than ten seconds.
The mites are either dislodged from the bees (e.g. when on top of the bees'
thorax) with the maximum centrifugal force, or remain in a safer position between
the bees' segments. Since the duration of centrifugation does not increase the
force, it is logical that after 10 seconds
the duration does not play any significant role.
The qualitative detection
efficiency (% detected in infested samples) is 100% for the infestation level
above three percent (n=93). Even at one percent infestation level the efficiency
is more than 85% (i.e. 13 positive detections out of 15 samples). This decline
is due to high fluctuation in detection rate in low infestations. The detection
rate (0%-100%) is based on only one mite in the sample. The quantitative detection
efficiency (% detected in an infested sample) under optimum conditions was also
>90% for the infestation levels above. three percent. while in the ether
roll method it is 35% (Herbert et al.1989). Figure 3 shows the general level
of the quantitative detection efficiency in relation to frozen and live bees,
performed by lowest speeds (5718, 5076 and 4752 rpm) and low detergent concentration.
which were less efficient for the detection. Out of nine observations in the
category 15-20 mites per 100 bees, five have been performed with the poorest
speed (4752 rpm) and time, hence the cause of the declination in the detection
efficiency. The true quantitative detection efficiency of the method should
be performed with the best speed 6342 rpm and high detergent concentration with
frozen and live bees and higher number of observations in each infestation category.
In spite of the high accuracy of the proposed method, nevertheless, as in ether
roll method or brood method, subsampling of a colony is a limiting factor in
low infestation levels. On the other hand, infestation levels under 3% may not
be critical. The speed of 6342 rpm along with the higher concentration of the
detergent solution was the most effective in mite detection. However, operating
at 6342 rpm was difficult with the prototype device as the lid was not securely
locked and had to be held by hand. Hence most of the experiments were conducted
at velocities of 5718, 5076 and 4752 rpm. A preliminary research at 7272 rpm
was examined and rejected since the excrement of bees necessitated filtration
of the liquid to view the mites.
and low costs were advantages of the detergent solution over other methods (e.g.
ether roll method, shaking methods). Mites were counted on the bottom of the
transparent rotational chamber. Unlike the hand-shaking method where foam disturbed
the operation (De Jong et a1.1982) in mechanical centrifuging, no annoying foam
exists. A preliminary observation using the hand-shaking method, produced foam
which hid and prevented mites from sinking. Often mites were encountered on
bees after removing the bees from the rotational chamber.
efficiency of this method with its ten seconds of processing time suggest that
it may serve as a better laboratory method for varroa detection. It is easy
to apply at the apiary or laboratory, especially in the spring time when bees
are vulnerable to sampling. It is not necessary to examine the bees immediately
like in the ether roll method (USDA 1987) and the efficiency of the stored sample
in the freezer is even higher. The impact of immediate freezing on mite detection
still needs research, if of interest.
method with the low detergent concentration, even after 60 seconds of rotation,
more than half of the bees will revive if placed in the sunshine or a warm place.
It may be better to rinse the bees with water and place them in a dry warm place.
This is true for mites as well, so be careful not to replace them in the colony.
this Finnish invention to beekeepers and apiary inspectors and encourage mass
production of the device and will answer all communication if more information
is required. Farmcomp Ltd. in Espoo, Finland is a potential producer of the
device and able to produce a few hand made devices at high costs or volume production
if needed. However, as the device works with the car battery, its use is limited
for the apiaries that are near a road. I hope other manufacturers can solve
this problem by using rechargeable batteries or extension cords, even though
this is not essential.
H. Hokkanen, A-L. Varis, J. Helenius, K. Heliovaara, A.
B. Mukherjee, J. Junttila and F Gates at the University of Helsinki,
S. Korpela at the Agriculture Research Centre Jokioinen Finland,
and R. Cox at the USDA - Iowa for their valuable comments
and cooperation in the research. I am thankful to Farmcomp Ltd
for manufacturing the prototype device. I am grateful for the supports
of the Foundation for Finnish Inventions (Keksintosaatio),
and Finnish Cultural Foundation (Suomen Kulttuurirahasto).
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