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Beekeeping methods Landrace The Driest The Wageningse Eng Varroa mite

The year 2023

Sun and frost on The Driest.

The year 2023 has been a good year for bees and beekeeper alike. All 11 hibernated colonies have survived, but one had been seriously weakened by chalkbrood. Therefore, I had to eliminate this colony.

There was a lot of rain this year. This was not only beneficial for nature, but also for the main honey flows in spring and summer and on the heather. Only a dry period from mid-May to the end of June caused a break in the development of the vegetation.

Due to the warm autumn, the colonies continued to breed for a long time, which resulted in high Varroa pressure, which had to be reduced by using oxalic acid in almost all colonies in December, during one of the rare cold mornings. This year I did not perform three-day mite counts on the Varroa board in autumn, but only monthly counts. This is certainly less accurate and does not allow for the construction of mite drop curves, but it is considerably less work…

All young queens on The Driest are locally mated. I didn’t bring any virgin black queens to the Neeltje Jans mating station this year. This had to do with the fact that I had created a lot of brood splits to relax the production colonies and thus suppress the swarming mood. As a result I had obtained many small splits. What also plays a role is that I have some doubts about the quality of the breeding material from Texel: the colonies are selected exclusively based on morphological characteristics but not on behavioral characteristics. The result of the local mating was very good: only 1 of the 14 young queens was not fertilised.

I have not made any temporary splits: all young colonies have been made by tapping bees and brood. This resulted in many small splits, but these can easily be united in autumn into colonies that are strong enough to hibernate.

This year we grew summer barley on our plot. The drought in May-June resulted in the crop remaining very low. When it started raining again in July, the weeds quickly started overgrowing the barley. This made it a bit of a challenge whether the quality of the grain would be sufficient, as the barley barely became dry enough. In the end we harvested a mediocre, but qualitatively acceptable harvest.

We sowed winter rye in October. Let’s hope that the heavy rain of winter 2023-24 will not throw a spanner in the works…

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The Driest Varroa mite

Varroa on The Driest winter 2022-23

The Varroa load was high this year, because autumn stayed warm for a long time. As a result, the colonies continued to breed for a long time, which played into the hands of the Varroa population. The consequences of this will become apparent in the spring of 2023.

I determine the Varroa pressure solely by counting mites on the bottom board. Hence, the natural mite drop, determined over a long period, from the beginning of autumn to deep winter, and also from the beginning of the year to late spring. I convert the counting results into the average mite fall per day. There appear to be large fluctuations, resulting in an erratic curve. That is why I also calculate the 12-day moving average and the cumulative mite fall over the entire counting period. These values give a much more reliable picture of the dynamics of the mite population. This makes differences between colonies more clearly visible.

The cumulative mite drop generally shows an S-shape, as we often see in nature. After a slow start, a more or less steep slope follows, which eventually flattens out again. In some colonies the curve is linear, so a straight line, without flattening. Still other colonies show an exponential curve, leading to an explosion of mites. Colonies with these kinds of curves drop out for propagation.

At some point of time in fall or early winter, the mite drop per day decreases. This is a sign that the brood nest is decreasing in size. The mite fall per day will remain low from now on until brood appears again in spring. The often used threshold value for chemical control of 1 fallen mite per day in December seems rather strict to me. In addition, this value does not take into account the size of the bee colony. After all, in a large colony more mites fall than in a small colony. That is why this threshold value is not very useful in practice.

In fact, each colony shows its own mite drop pattern. The issue now is whether these differences in mite drop patterns per day are indicative for the ability of the colony to deal with and survive Varroa. By now, we know from research that untreated colonies develop various mechanisms to survive Varroa.

The cumulative mite drop curves previously discussed are defined by a number of parameters: a_ = the curvature at the beginning of the curve; b_ = the deflection at the end of the curve; r_ = the rate of mite drop (in mites per day), i.e. the steepness of the curve; Y0 = the mite drop at the start of the count; and K = the maximum number of mites fallen.

Absolute (left) and cumulative mite drop (right) of colony 22-06 from 10/10/2022 to 26/12/22. Highest average mite drop was on 22/11/22. Parameter values of the curve are: a_=0,62; b_=066; r_=0,36; Y0=17; K=213.

Below, in a graph for 8 untreated colonies in my apiary, the values for (a_, r_) are plotted, with r_ on the horizontal and a_ on the vertical axis. All r_ values above 2 are bad in my estimation. Based on this assumption, at least the colonies 22-02, 22-05 and 22-08 are eliminated for propagation. The colonies 22-03 and 22-06 have a low a_ and a low r_ and are therefore eligible for propagation, provided they are also satisfactory in other respects, of course.