> do you see that the crystals indeed evaporate/sublimate?

Yes - but it needs the warmth from brood below.  If there is no brood then it is very slow regardless of external temperature; conversely, brood plus a low external temperature gives good sublimation.  It is another reason to treat early, so we treat colonies after the crop is removed in August (which of course is also desirable to produce clean winter bees).

Any colonies taken to the heather moors will not be treated until they return - often mid-September when it can be much cooler, but that does not matter as they usually come back with plenty of brood which will keep temperatures up in the hive.

Best wishes

Peter 
52°14'44.44"N, 1°50'35"W

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