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Photo D. The 'cappings scratcher'
method for surveying for mites. |
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Monitoring and Thresholds
Survey methods provide presence/absence information. One such method
is the “cappings scratcher,” which requires one to impale
a number of capped drone cells with a cappings scratcher, and then
to pull the immature drones from their cells for examination (photo
D). This method has been found to be highly effective in detecting
mites when present at very low levels. A second survey tool is the
“sticky-board,” which takes advantage of the fact that
mites often fall off of bees. Typically, a piece of paper is covered
with a sticky substance (petroleum jelly or a vegetable spray) and
inserted into the hive where it rests, sticky-side up, on the bottom
board. The sticky-board must be protected from the bees. One way
to do this is to build a wooden frame, cover one side with 1/8”
hardware cloth, and attach the sticky-board to the other side (photo
E). Sticky-boards are also available commercially. The board
is removed after 24 or 48 hours and the mites are counted. Strictly
speaking, the sticky board does not provide information about pest
density; however, it is often used for that purpose. Lastly, mites
can sometimes be seen on adult bees or walking on the comb, but
this is more common when infestation rates are very high and should
not be relied on as a diagnostic method.
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Photo E. The ‘sticky
board’ used for surveying for mites. |
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Sampling methods provide an estimate of pest density. This is the
type of information needed to determine whether to apply a pesticide.
One method is the “ether-roll,” which provides an estimate
of pest density in terms of mites per standard volume of bees. Bees
are collected from two or three brood-nest combs and placed in a
quart glass jar. If only a few colonies are being sampled, shake
bees directly into a dishpan. Scoop up ½ cup of bees and
quickly pour them into the quart jar. If larger numbers of colonies
are being sampled, a modified “Dust Buster” (DC Insect
Vac from BioQuip®) can be used to collect a standard volume
of bees, which are then transferred to the quart jar. You will need
to experiment with the vacuum collector to determine the exact volume
that yields about 300 bees. Spray a three-second burst of an automotive
starting fluid into the jar, replace the lid, shake vigorously for
10 seconds, and then toss and roll the jar three times along its
long axis. Mites, if present, will be seen adhering to the sides
of the jar (photo F). This method detects
50 to 60% of the mites actually present in the sample. The resulting
ether roll count is usually converted to a standardized 300-bee
ether roll count (SER) using the formula:
SER = (ER) / (#B/300),
where ER is the ether roll count for the sample and #B is the number
of bees in the sample.
An improvement in accuracy can be obtained by calculating the actual
mite-to-bee ratio. This is done by collecting the bees as above
and then separating the mites from the bees by agitating them for
five minutes in a container with soapy water or alcohol and straining
through a 1/8” hardware cloth screen. The screen catches the
bees but allows the mites to pass through. Typically, bees are washed
several times to remove all of the mites. Mites and bees are counted
and the actual mite-to-bee ratio is calculated. You can convert
the mite-to-bee ratio to a standardized 300-bee ether roll count
using the formula:
SER = ((R * #B) / 1.783) / (#B / 300),
where R is the mite-to-bee ratio in the sample and #B is the number
of bees in the sample. The conversion factor (1.783) is from Calderone
and Turcotte (1998) [1].
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Photo F. Mites adhering
to the sides of a jar in the ether-roll test. |
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Remember! For an estimate of pest density to be meaningful, each
step in the sampling method must be standardized. This means monitoring
mite levels at the same time each year, and monitoring all colonies
exactly the same way. For the ether roll, this means collecting
samples from the same place in each colony (tow or three brood nest
combs), collecting the same number or volume of bees in each sample,
applying the same amount of starting fluid, and shaking the jar
in the same manner. For the sticky-board, the same size board must
be used each time, the sample must be collected at the same time
each year, and the board must be left in place for the same length
of time.
The decision to use or not to use a pesticide is based on an economic
threshold. This is the pest density at which economic damage is
expected if a treatment is not applied. Economic thresholds for
V. destructor vary widely throughout the country. The values used
below are based on studies conducted in the Midwest and Northwest,
where blooming patterns, length of winter and winter temperatures
are similar to those in the Northeast. Significantly different values
are used in other parts of the country. Beekeepers should contact
their local extension apiculturist for the most current recommendations
for their area.
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