Counting
Varroa Mites
FROM
ALLEN DICK’S DIARY----- OCT 2003
We picked up the varroa mite drop boards this morning and looked
them over. The first batch of five sticky boards showed 10, 6,
2, 0 & 2 mites over three days of natural mite drop, and the
second batch showed 0, 0, 1, 1 & 3. The third showed 0, 0,
1, 1, & 4. The boards had been in for three days and, therefore,
each result should be divided by three then multiplied by 100
(the estimated average varroa lifespan ) to estimate total mite
loads. Thus the worst hive could be assumed to have a 333 mite
load. That is nowhere near serious. 350 mites as a total load,
is very light, in fact. A visit to the varroa calculator gives
a different perspective, but it also assume drone brood, which
we no longer have at this time of year.
Counting is always difficult when there are so few mites, and
we are always tempted to count the immatures -- the occasional
mites we see in the board that were almost fully developed in
a cell when the host bee emerged, but which die immediately of
exposure, when deprived of the special conditions inside a cell.
Such mites have the shape, and often the size of mature mites,
but are pale and translucent. We know they did not live even one
day after emerging, and were never part of the adult, reproducing,
population. Since their lifespan is zero days, the 100 day estimated
average lifespan multiplier does not apply, and I figure immatures
should not be counted.
By this time of year, there should be very little brood in which
mites can hide, so most varroa should be phoretic at this point.
When the mites are phoretic -- on bees, and not hidden in brood
-- they are at their most vulnerable, and have the highest mortality
rates, so, even using a multiplier of 100, which could be high,
we are seeing very low infestation rates. Over winter, the mites
will be under even greater pressure, as they occasionally fall
off bees and are exposed to the cold conditions at the hive floor,
unless they are able to grab back onto another bee.
For some reason, varroa is not giving us much trouble. For the
past several years, the only treatment we have used is a single
Apistan™ strip placed in the centre of the cluster in the
early spring and left for 42 days. Our tests always show very
low levels of mites, much lower than when we used two strips in
the fall plus several formic treatments. Granted, we had a dry
year in 2002, and we spilt heavily this year, and both these factors
tend to reduce varroa loads, but, nonetheless, we did not split
all hives, and when everything is considered we still are seeing
lower levels that we would expect and lower levels than we saw
in the past.
The drop boards we use are just Coroplast™ sheets cut to
roughly the size of a sheet of foundation, with a tab of Duct
tape added, and with a piece of 6 mesh hardware cloth sitting
on top to keep bees out. The screen has been bent to be a bit
dish-shaped so that it sits up above the board about 1/4"
so the bees will not contact the salad oil/Vaseline™ mix
which is smeared onto each board before it is placed under the
hive, to catch and drown falling mites.
To insert the boards, we just hold the hive floor down with one
foot, if necessary, and tip the hive back a bit. It does not matter
if some frames touch the screen when the hive is lowered. As for
catching all the mites, we centre the boards under the cluster
and figure if we miss one of two mites, that this will not grossly
affect our estimate. This is not rocket science. We're just looking
for a rough indication whether to expect trouble, or not worry
for another six months.
OOPS
Ignorance is a terrible thing. We printed some pictures
of a pollen trap in the April "Buzz". Dennis Arp called
to let me know that the trap was upside down when we took the
pictures. I stated in the write up that there weren't any stripper
screens. Well, there are. I just didn't look closely at the path
the bees had to take. In the picture the screens are shown on
the bottom. I thought they were ventilation screens for use in
a hot climate. Dennis also pointed out that the screen on the
top of the pollen drawer was seven mesh. I had just assumed it
was eight. Some of the pollen granules are too big to get through
an eight mesh screen. We also talked about storing pollen. It
is a significant part of Dennis' income. When it is clean and
dry, it goes into barrels. They put a piece of PVC pipe down the
center of the barrel and dump two or three pounds of dry ice down
the pipe. The lid is set loosely on the barrel. The dry ice converts
to Carbon Dioxide and forces the air from the barrel. Then the
lid is secured.
Submitted by Phil Ebert
