Feeding dry sugar was/is quite a common emergency strategy for helping out a starving or underweight colony in winter if you’re too lazy or disorganized to make candy boards. The rationale is that the bees can’t process a syrup – it’s too cold and damp, and their invertase works very, very slowly. The crystalline sucrose is just dissolved and consumed it seems, water being collected from outside or from condensation inside. I used to buy 1kg bags, cut a cross in one side with a penknife and tip in about 100ml of water. This would bind the sugar so that I could just invert the packet and put it on the top bars or over a feeder hole in the hive cover-board. The other reason for dampening it was that if you didn’t the bees would pick up the loose dry crystals in their mandibles and dump them outside as trash. They didn’t eat it at all.
There is a relevant study in the Journal of Apicultural Research, J Simpson, (1964), ‘Dilution by honeybees of solid and liquid food containing sugar’.
The only place I’ve ever come across ‘raw’ sugar being used is in New Zealand, and no one has ever been able to tell me why ‘raw’ is used in preference to plain white granulated stuff. Using raw is counter intuitive for me because of the impurities left in it (if it is genuinely ‘raw’).
Just as another observation, I have had colonies starve out leaving crystalised oil-seed rape and ivy honeys; dry nodules of sucrose left in the honey cells. Why didn’t they eat that if they use granulated sucrose?
The other thing I’m interested in is the honey testing. We are told sucrose is detected in honey from syrup fed pollination units, is it really not being found in dry-fed colonies? Testing honey for sucrose was something no one bothered about in the old days, now tests for adulteration pick it up. As honey has several sugars, glucose, fructose, sucrose, and others, I’m not quite sure quite how sucrose ‘contamination’ is telling us something, but the authorities think it is.