For field samples, the hand shaker shown in these pictures is hard to
beat and I would imagine these jars could be shaken by a simple machine.
http://www.honeybeeworld.com/diary/images/2009/DSCF4899.JPG
http://www.honeybeeworld.com/diary/images/2009/DSCF4897.JPG
http://www.honeybeeworld.com/diary/images/2009/DSCF4889.JPG
http://www.honeybeeworld.com/diary/images/2009/DSCF4902.JPG
The jars are cheap and when we were doing the field samples, we went
out with boxes of the jars pre-filled with alcohol and did the shakes,
then lidded the samples and put them, back in the boxes to be
re-examined in the lab. (note: if the alcohol is cold from sitting
outside in a vehicle overnight, the mites do not come off the bees as
readily as when the alcohol is warmer.)
These shakers are designed for a 300-bee sample, but in my experience,
counts are most consistent using 200 to 250 bees due to the screen
size. Of course, for smaller samples, the calculations must be
adjusted, and a smaller sample may not be as representative, so there is
a trade-off here.
These shakers are easy to make, but I would recommend using a jar of the
same capacity, but with a wider mouth if such jars can be found. In my
opinion, a slightly larger screen area would be better for the standard
300 bee-sample.
The shaker shown in the pictures has about one inch of bees on the
screen (300 bees) when draining the alcohol and mites through to the
lower jar for examination. IMO, that one inch is the maximum thickness
of bees that will allow essentially all the mites to flow with the
alcohol under all conditions.
Half that thickness of bees (1/2") would be better, and that can be
achieved by simply doubling the screen area. These jars are 70 mm
inside, but have a 63mm mouth. That small difference reduces the mouth
to 80% of the area of a similar jar with straight sides. To double the
mouth area from this model, a jar with a 89mm diameter mouth would be
required, and IMO, would be more accurate.
Nonetheless, these jars are plenty good enough for our purposes.
FWIW, some people tend to think a larger sample should be more accurate
and wash more than 300 bees, but the resulting mass of bees can act as a
filter and prevent some of the mites from going through the screen with
the alcohol, resulting in a false count. Bigger samples need a larger
screen area.
Back to the shaker table
Actually all that is needed to shake jars is a deck of some sort
standing on on four springs with a motor attached somewhere driving a
shaft rotating at the desired frequency.
If an off-centre weight is mounted on that shaft, the table will shake,
the amount of shake being set by the amount of weight and the distance
from centre of rotation.
To vary the direction of the shaking and create swirl, the motor and
shaft can be set at an angle to the table, possibly with a hinged
assembly for adjustment.
To generate a hard shake, an adjustable soft or hard restraint block can
be added to provide a hard limit to the table movement in one direction,
creating a "knock"
Some sort of jar hold-down is necessary and could be as simple as a
sheet of semi-soft foam on a board placed on top of the jars and
fastened by some simple method.
Perhaps the idea is design a shaking table that separates the mites from
the bees so that there is nothing to do but count. That is a bit more
difficult.
***********************************************
The BEE-L mailing list is powered by L-Soft's renowned
LISTSERV(R) list management software. For more information, go to:
http://www.lsoft.com/LISTSERV-powered.html
Guidelines for posting to BEE-L can be found at:
http://honeybeeworld.com/bee-l/guidelines.htm
|
