>The question:
>>Does anyone know if dry ice is cold enough to do hygienic testing?


Allen asked me to respond.

Dry ice is hard to control for this purpose.  If you put it on the brood,
it takes a long time.  Worse, you get partial kills over a large area of
comb, which really messes up the test -- instead of a known number of DEAD
brood cells in a small area, you get an uncontrolled number of dead and
dying brood in cells.

Liquid nitrogen always worked in our trials, but we stipulated using a
smaller area and more liquid nitrogen than most of our successors.  One
application and we killed all brood within our treatment 'tube', sometimes
penetrating to the back or opposite side of the comb.

However, everyone misses the point that our data shows that three separate
small areas of flash frozen brood produces a more accurate and reliable
test than killing one large area.

Medhat took the liquid nitrogen freezing another step.  He was concerned
about partial kills, so he came up with a strategy of multiple freezings,
using a butter dish.   More than one application of cold is an insurance
policy -- if you don't get them the first time, a 2nd application drives
the cold on through.

We developed this test under funding from EPA.  We had tried the Tabor
method of cutting out sections, freezing them overnight, and re-inserting
into the hive.  Many of our colonies responded to the damaged comb -- cut
the comb and the worker bees started tossing out brood (whether dead or
alive).

We try hard to minimize comb damage to avoid false results.  The larger the
area affected, the more likely you are to find that the bees are again
responding to changes in the comb, rather than dead brood.  We haven't
found a practical way of eliminating comb damage, but at least we can be
sure that its consistent (the same) for every trial.

Jerry

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