We have already written several times about a new version of the old and previously not very convincing method of controlling the quantity of Varroa mites in bee colonies based on counting of the mites, falling free on a sticky board. Why not too convincing? Because everything in this method is unproven and simply taken from nowhere .... Why a mites drop of 5 mites per day is acceptable and 6 per day is already very bad, and 10 mites per day is critical ... No explanation. .. It is simply proposed to multiply this figure by a certain coefficient and you will get a lot of mites in the hive ... We are going the other way.
Based on the data obtained by us during several years of experiments, it can be argued that the mites drop in the hive is not uniform, but consists of two main types of mites - young undeveloped or non-fertilized females that did not take part in the increase of the mites' population, and from dark burgundy old females that took part in several breeding cycles and have already outlived their term.
The main type of the mites in the mites drop, that we are used to see - is maroon old females, which die from old age and fall to the bottom of the hive. Here, too, not everything is clear. Some of these females can be seen evenly scattered over the entire surface of the board. These females die while feeding on the bees and fall down, most likely due to death from the limiting age. Sometimes, a part of them, just fall down alive and dies on the board from hunger. Another part of the dark mature females can be observed tightly grouped in even rows, lying exactly between the brood frames. These females most likely died in a closed cells during the laying of eggs and apparently managed to give life to the next generation of the mites. They, as well as immature females, are thrown out of the cells by the bees.
The quantity of these maroon mites falling down on the sticky board can be directly related to the size of the mites population in the bee colony. The growth of quantity of such mites falling down on sticky board indicates an increase of the population of the mites, but its decline or termination does not unequivocally mean that the quantity of the mites have become less or they have completely disappeared. It can just mean, that the remaining mites are young and full of strength ... and will not die soon. That is why we do not want and do not recommend to use the number of mites falling on sticky board for prediction of specific values of their population in bee colonies.
Let's consider now the second type of mites, that can be found on sticky board. Usually, when Varroa mites use for breeding the cells of worker bee brood, at the end of the mite development cycle in a closed bee cell, remains one underdeveloped or unfertilized female mite. Bees throw it out of the cell when cleaning the cells after the young bee left the cell. On sticky board could be found undeveloped individuals even more pale than unfertilised young females . These are deutonymphs. As a rule, they end up on the board due to unfortunate conditions for development. Most likely, this is an unsuitable thermal regime in the brood cells, which are very far from the center of the brood nest ... In our opinion, this means that the mites have occupied the entire central part of the nest and have moved out to its periphery ...
Usually, the drop of this type of mites indicates a sharp increase in of the mites population, which filled up the center of the nest, and spread to its borders, where it is colder and conditions for the development of young female mites are worse. The growth of this particular type of mites in the total amount of mites drop, together with a small number of old dark mites, indicates an upcoming powerful surge in the growth of the mites population in the bee colony. From this moment on, it is necessary to take emergency measures to neutralize the mites.
As a rule, the growth of free fall of a pale-colored mites precedes the growth of free fall of an old maroon mites by 15-20 days ... This is a very good indicator for predicting an increase of the quantity of Varroa mites and the imminent appearance of an emergency in a bee family! This is especially important for those who do not use, or don't want to use chemicals for mass and repeated treatment of their bees.
On the picture you can see the graph of a separate count of two types of mites for five bee colonies over a year and a half. But the most indicative are two graphs - the graph for the E-1 family and for the 8-1 family. Let's consider the E-1 schedule. It is clearly seen that in the interval 13-14 (April) the growth of free fall of mature mites is not observed, while the increment of free fall of an immature mites warns about the beginning of the mites population growth, which occurs in the interval 14-15 (May) and especially in the interval 15-16 ... (June) This bee family did not survive after point 16. The infestation level became fatal for it. Schedule for family 8-1 is flatter. The initial infestation level of this family was lower. But on the interval 13-16 (April-June), it shows the same tendency as the E-1 family - the growth of free fall of an immature mites outstrips the growth of free fall of a mature mites and predicts a significant increase of Varroa mites population. The trend was interrupted by the removal of drone brood, but as can be seen from the graphs, this only delayed the explosive growth of the mites population in this family until the end of honey harvest. This pattern is typical for the spring development of the mites in a bee colony.
So, for a practicing beekeeper, this means that if in the spring, pale-colored and/or translucent mites appeared in free fall on sticky board, then urgent measures must be taken to combat Varroa mites. This is a sign, that after 2-3 weeks, the growth of Varroa mites population will become fatal for the family in the absence of measures to combat it. It doesn't matter how many mites you will see on sticky board. The less the better ... As long as there are no pale mites in free fall, you can still calmly do your job. But when they appear, the fight against the mites must be started urgently! Otherwise, the bee family will die.
The same situation is possible after honey collection. But at this time, it is warm enough and the death of young and immature mites decreases. Therefore, the growth of free fall of the mites can proceed in parallel in groups of mature and immature mites in any quantity. But despite this seasonal difference, the appearance and growth of free fall of immature mites suggests that the beekeeper needs to take action urgently.
We assume, that the adoption of measures - is primarily the selection of all brood, sealed and open, from the families which should work on honey collection into one family (or several families, depending on the size of the apiary), followed by treatment of only this family with formic or oxalic acid. This will drastically reduce the quantity of varroa mites in working families and will leave them free from chemicals and acaricides, with which are usually treated all families of the apiary, and which strongly worsening the condition of bees, (and sometimes killing them) and which are making honey unsuitable for export.
Thus, the control of the appearance and growth of free fall of pale immature or infertile mites - is an excellent indicator of the moment when anti-varroa measures become vital to maintain the strength and vitality of bee colonies. And while it is not too late, beekeeper can use environmentally friendly methods of dealing with Varroa mites, and that is not unimportant !
Copyright Sergey Glebskij 2021
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