> In a Langstroth hive with a dark-colored 3/4" wooden cover, I've measured
> temperatures easily exceeding 160F on the top of the cover.  At such a
> temperature, wax melts into liquid.  On the underside of that cover in an
> empty (no bees) hive, the temp can reach 145F, and the temperature of the
> top bars roughly 1/8" below can reach 122F.

Although this was submitted in another context, the numbers provided can 
help explain why people report variable experiences with applying formic 
in pads on top bars.

Those temperatures are bound to drive off almost all the formic in a pad 
very rapidly, so a person who applies the pads before noon on a hive 
with a dark, thin lid and no pillow or inner cover, waxed-up top bars 
and limited ventilation above the top bars will have very different 
results from a person who applies the same pads in late afternoon in a 
hive with clean top bars,3/8 clearance, and an inner cover or an 
insulated white lid.

The upshot of the above observation is that one cannot assume that 
simply placing two pads with formic on the top bars of any hive will 
accomplish the intended task, or do so without serious collateral damage.

Understanding what is happening in a hive and the effects of sun, wind 
and populations along with hive variations is important when using formic.

(Incidentally, due to a different mode of distribution through the hive, 
Apivar will not be affected much if at all by such differences).

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