In response to requests from the members at the February meeting, I started working on this article about three weeks ago; reading journals and pillaging the Internet for information.  None of the advice below has any references because of the commonality of the information.  Fairly quickly I discovered that the most common causes of individual bees dying in a colony during winter and early spring are: starvation, disease, cold and pests.  Other reasons are failing (old) queens and wet hives.

A little more research revealed that I should dig deeper to determine how a beekeeper could make the decision that the kill was caused by, say, cold weather and not a failing queen, or vice versa.  That lead me to the need for conducting adequate Fall Management so that, in the Spring, the beekeeper can deduce what he/she did not do effectively (such as varroa mite control) back in October could be the cause of the winter kill, if you see where I am going with all this.

But to return to the common causes of winter kill, the following:

Starvation: It is not uncommon to examine a colony that died during the winter and early spring and discover the dead colony was close to stored honey. It had been too cold for the bees to move into the stored honey. How do you know if a colony starved to death? Most of the bees will still be in a cluster formation and will be head first in cells, attempting to stay warm and eating the last drop of honey out of the bottom of cells.

Disease: Nosema is hard on the winter cluster because Nosema is worse when bees are confined and cannot defecate. Nosema is a gut disease so it is most deadly during late winter. If the Nosema level was high in late fall, this can cause bees to perish during the winter and early spring.

Cold: Bees do not heat the entire inside of the hive, but only the area within the cluster of bees. On warm winter days the winter cluster breaks up and bees begin to search for stored honey on other frames.  If there is a sudden drop of temperature the colony sometimes cannot re-form into a tight cluster. Bees might be stranded to freeze to death or the colony may become divided into several clusters, each too small to produce the heat needed.

Pests: Varrora and Trachea mites are extremely hard on the winter cluster and can lead to bees dying. These pests need to be controlled during the summer and early fall to reduce the infestation level.

Failing Queens:  A young, strong queen entering the winter has a far better chance of heading a strong hive in the early spring, leading to bigger crops. An old queen in the winter will certainly not improve before the spring.

Weak Colony: A hive seems to need a ‘critical mass’ to be successful. So if the hive is small because of queen problems a better solution might be to unite the weak hive with a strong one after culling the worst queen. One strong hive is better than two weak ones, and can always be split come the next year.

Winter condensation: If you seal your hive too tightly then you increase the possibility of overall condensation within the hive.  Cold water accumulates on the bottom of the inner cover and drips onto the cluster.  That eventually kills the colony.

There is nothing you can do to help your bees once they have clustered and it is cold.

The fact is, most hives that die do not even die in February. They die in March, when they have exhausted their food supply and have too small a population to forage the early nectar on the occasional warm days.  Naturally, the cluster is very small in March, and if there is a severe cold snap, a very small cluster cannot stay warm. They are too small because the queen stopped laying early, probably in August or September and the bees simply died of old age reducing the number in the cluster. Work your hives in the fall so that the queen continues to lay into October and November. The easiest way to do this is to feed the hives pollen patties and 2:1 sugar water.

How to prevent or minimize winter kill

Ø    Install a mouse guard at the entrance by November 1, at the latest

Ø    Remove queen excluders.

Ø    Remove honey supers.

Ø    Check the frames or lift the hive at the back to see if it has enough stored honey by its weight.

Ø    Treat for mites for at least three weeks ahead of the expected below 50F temperatures.

Ø    Provide sugar syrup with apple cider vinegar of other nosema treatment

Ø    Wrap the hive with some sort of insulation or roofing paper.

Ø    Build a wind break (depends on siting of hives)

Ø    Provide a good Fall examination for disease and treat.

Ø    Treat the hives 3 weeks in a row with powdered sugar for mite control. This is best started in August.  Use about a cup of confectionary sugar per colony and load on the top bars then brush between the frames.

Ø    Many beekeepers requeen annually or biannually, depends on the strength of the hive; it might not be necessary if the hive has performed well during the year.

Ø    Use local queens from overwintered colonies.

Ø    Keep bee colonies strong:. Some beekeepers make many splits to replace their dead outs and to increase their number of colonies. This process could weaken the parent colonies and affect the bee population buildup. Additional feeding of pollen supplement and sugar syrup to bee colonies is required to offset some of these negative effects.

Ø    Development of winter bees: Beekeepers need to make enough room in August and September for the queens to lay eggs to produce winter bees. Winter bees are physiologically different from summer bees. They have a tolerance to withstand the winter.

Ø    Feeding bees: Beekeepers should provide the feed (2:1 sugar to water) early enough to ensure that bees are able to complete feeding before cold weather arrives. To successfully survive the winter, bees must feed and store all medicated (essential oils) feed in the bee colonies. When considering feeding protein supplements, beekeepers must ensure there is enough of a natural pollen supply for the production of young bees. Poor flying conditions and drought may also cause pollen shortages. Therefore, the feeding of protein supplements should be seriously considered by beekeepers.  Turn the inner cover upside-down so that the wooden rail is down, allowing more of a gap between the frames and the inner cover to accommodate the spacing needed for the patty, or use an Imirie shim.

Ø    Ventilation: Make sure that your hive has some sort of upper ventilation to allow the dampness from the bees’ respiration to leave the hive. A rock on the inner cover can work.  Leave screen bottom boards open all winter. 

Ø    Brood space: If all your frames are filled with honey and pollen this leads to the loss of brood area and that will reduce the volume of young bees going into winter, this in effect forces the hive to winter older bees, reducing the population of young bees which will be necessary to feed brood early in the spring. So it is not a good idea to remove supers too early, better to leave one in place till after first frost, the bees will prefer to move stores upwards rather than fill any brood space with permanent honey.