I remember Jazz was talking about designing something of the sort. I know the typically quoted temperature of an active brood nest but not the temperature of a broodless cluster. Presumably under 32 degrees. Usually in the summer period if there is no brood present the bees seem looser and aimless on the comb anyway. Out of interest, do you check for brood before treating? I never have, perhaps if it continues to be as madly warm as at present in December, I will take a frame out when I go in.NigelP wrote:If there is brood your brood nest will be at 32-35C, so a simple cordless thermometer will tell you what is likely to be going on or not as the case may be. IIRC there is usually a sharp increase in hive temperature shortly after the winter solstice to 32/35 when brood rearing starts in earnest.
I usually treat with oxalic between Christmas and New Year as it is around the shortest day and I am available to do it.