Winter Losses

In Austria, the winter loss rates of honey bee colonies have been recorded for ten years. The results of the winters 2013/14 to 2016/17 are presented here. The loss rates of hibernated colonies range from 8.1% (winter 2015/16) to 28.4% (winter 2014/15). From winter 2013/14 to winter 2016/17, 5227 data sets concerning 83,850 hibernated bee colonies were examined for their representativeness, the geographical distribution of the losses, accompanying symptoms of the winter losses and the beekeeping operation over the entire investigation period. Particular attention was paid to the influence of Varroa treatment methods on winter mortality.

Amount of the annual winter losses of honey bee colonies in Austria 2007/08 to 2017/18 in percent.

A negative correlation the winter loss rate and the sea level of the colonies could be found. Also negatively correlated was the size of beekeeping operations with significantly lower losses for operations with more than 50 colonies compared to those with fewer than 20 colonies. Migratory beekeeping has no influence on the winter loss rate, but maize, rape and buckwheat as traditional plants represent a risk factor.

During the study period, honeycomb hygiene measures such as the removal or replacement of old, formerly incubated combs by new ones were neutral. Formic acid was the most common method used to control varroa in summer. Clear advantages were found with formic acid long-term treatment alone compared to formic acid short-term treatment alone. Oxalic acid treatment for residual mite removal had no effect on overwintering success in the respective winter.

Treatment with hyperthermia and a single thymol treatment showed no clear positive or negative effects on the loss rates in the respective winter. The determination of the varroa infestation rate paid off in three out of four winters in terms of lower loss rates. The success of the drone brood removal used by more than 60% of the participants onto decreasing winter losses was questioned. The use of other biotechnological methods (e.g. trap comb method or total worker brood removal) proved to be positive for overwintering success, especially in the two winters with high losses.

The view into a colony empty of bees in spring - the colony died during the winter.
The rest of an originally strongly winterized colony at the time of the wintering out.
This colony did not survive the winter, many dead bees lie in the floor board of the beehive.