If you intend on feeding bees granulated sugar, you should only do so in emergencies such as when a bee colony is actively starving due to depleted stores of honey or nectar.
This typically happens during a nectar dearth or in the winter. Especially if you have practiced poor beekeeping and over harvested honey. All hives should be left with a full medium honey super to overwinter on at a minimum. Bees will even ignore granulated sugar, and will actually remove it from their hive if there are better sources of nutrition such as nectar or sugar syrup or even honey in another hive (robbing). You can be sure though that a starving hive will be a huge source of robbing behavior and this is easily preventable.
How do you prevent this robbing when there is no honey or nectar left in a hive. You can try feeding bees granulated sugar as an emergency food source in winter. Though you should only feed bees granulated sugar in emergency situations. Bees will always take sugar syrup though and the time it takes to make syrup from your granulated sugar is worth it. Just place the granulated sugar you have made into syrup into a hive top feeder if your bees are starving. They will be able to convert it to a usable resource much faster.
The best defense though from starvation for your bees is to never take more honey that you need, and to always leave your bees a full honey super to overwinter on. This does not mean leave them a whole honey super after the last nectar flow! Make sure they have a full honey super after they enter torpor and the queen stops laying!
Starvation is what I call one of the "Big 3". The three biggest things that cause the death of your hives over winter.
1. Starvation, easily the most preventable of the three.
2. Making your bees go into winter with a high Varroa mite load.
3. Thinking bees need to be wrapped up like mummies. This prevents adequate airflow in the hive and allows condensation, the third biggest killer. It is known that bees can generate 107f in the cluster in the winter, you do not need to bundle them up. What they do need though is to never get wet. They get wet in winter by condensation forming on your inner cover and falling onto them, which drops their body temperatures and causes them to die. It is better to have too much air-flow, than not enough.
So, in conclusion, if you are feeding bees granulated sugar to prevent starvation, good for you! Though next time, just be careful not to overharvest, and you won't need to.
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We did a 3-part series on wintering your hives and starvation was covered in one video, see below.