So,
we again want to consider the topic of analyzing the size of Varroa mites'
population and the possibility of using chemical methods to combat them, based
on data, obtained when counting the number of the mites, freely (meaning
without the use of acaricidal drugs) falling on a sticky board, located at the
bottom of the hive .
Now
it is mid-April, there are positive temperatures on the street, the bees
started breeding quite a long time ago, and the first Varroa mites of a new
generation appear in families. The uniqueness of this moment is that it is very
clearly visible that we have two different generations of the mites and three
different types of the mites in "mites drop". Let's take our
experimental apiary as an example. These mites were found on April 13 in Hive
E-1 ( our experimental hive). Let's consider situation more detailed ...
We
see that in the 9 days after the last inspection 75 fall down on the sticky
board, and it would seem, that we should say that the daily fall is 75 \ 9 =
8.333 mites per day ... A very large
number! In the spring, based on the recommendations of all
"reputable" organizations, an immediate chemical treatment is
required! But let's not be so hasty in conclusions! Look at the mites more
closely ... What can we say about them ... The fact is, that there are three
variants of Varroa mites on sticky board -
1)
The group of dead old, mature, fertilized, dark-maroon female mites-founders -
32 pcs.
2)
The group of dead young mites, of this year of birth, possibly unfertilized
females, which the bees threw out of the cells when cleaning honeycombs - 27
pcs. Among the light red mites, two
females were still alive.
3)
The group of dead immature female mites at the stages of deutonymph, as can be
seen from their very pale color - 16 pcs
Thus,
basing on our reasoning, we can argue that we are dealing with 32 mature
females, most likely, which became the
ancestors of one of the 2020 generations, and died because of old age. If you
count only them, then we will get the amount of "mites drop" 32 \ 9 = 3,56 Varroa mites per day. This is
not critical. In addition, we can say, that in the bees' family was started the
growth of new generations of mites, and at least 27 brood cells gave us 27
young females at the exit and, possibly, some of the founding females survived
too... The other mites can be still alive, and are on the bees and in capped
brood cells.
What
facts give us reason to believe, that pale-colored mites are young - 1) - unfertilized females, 2) immature
deutonymphs ... In order to find this facts, we again have to turn to
authoritative documents ....
(Managing Varroa. Published by The Food and Environment Research
Agency. Printed in the UK,
November 2010, www.defra.gov.uk/fera )
On the upper diagram we see once
again the confirmation of our practical results - 1) Varroa mites in the summer
live 2-3 months. In practice, we see about 2.5-3 months. 2) Immature and not
fertilized young females do not survive. 3) The final red-brown color of Varroa
mites is gained after the last molt ot the mite, when it become fully grown and
capable to lay eggs. Young females does not have such a color. They are paler. The color is closer to
brigh-red. Confirmation of this item we took from another document ...
(A deadly honey bee parasite The Varroa Mite PUBLISHED BY
Bayer AG beecare@bayer.com www.beecare.bayer.com )
"...Graphic
showing Varroa mite development stages The first development stage of the
Varroa mite is a six-legged larva that develops inside its closed egg. The
eight-legged protonymph emerges in the post-hatching second stage. In the third
phase this protonymph develops into a deutonymph, which then becomes the adult
mite. In the final nymph phase, the growing mite undergoes two immobile
transitional chrysalis stages (protoand deutochrysalis). Young female nymphs
are white in color and, after molting several times during the development
process, turn dark reddish-brown during the last immobile stage – the
deutochrysalis – and maintain this color as adult Varroa mites..."
Thus,
on the example of our results of collecting and counting of the mites falling
on sticky board, it can be stated with a high degree of certainty, that there
are two processes which simultaneously take place in the hive, the results of
which we can see in the form of "mites drop" on a sticky board:
1)
We see dead mites of a dark reddish-maroon color, which died a natural death
from old age, and represent -
•
Option 1 - dead mites of generations of the previous year, which left after
wintering, and gave birth to new generations of 2020, but this is unlikely,
since 7 months have already passed from the last exit of bees from brood and
from the last known fall on sticky board of young immature mites. But in
principle this is possible, since in another family in which the queen has
practically lost its ability to lay eggs, we see dark reddish-maroon mites in
the complete absence of young red female mites.
•
Option 2 - dead mites from the first generation of 2020, born 2.5-3 months ago,
that is, in January 2020, closer to the middle or to the end of the month ...
In
both cases, these mites should be taken into account and their number should be
used in all known models of calculating the mites' population in the bees'
family.
2)
We see fallen to a sticky board, dead, and still alive, young, most likely, not
fertilized females, as well as deutonymphs, which did not and will not
participate in the process of increasing of the mites' population, but can be
used as an excellent indicator that conditions in the bee family are such, that
the minimum possible number of female mites survives and become fertile. This
is a good sign. (If, in principle, the presence of mites in the hive can be a
good sign ...) These mites, which died not fertilized, should not be taken into
account in calculations, since they do not affect neither the state of the
bees' family, nor the size and growth of the mites' population.
At
the best moments for the development of the mites population, the bee family’s
life (in the temperate zone) in May and June (which, taking into account its
life span, leads to a powerful "mites drop" in August, September), we
do not observe the fall of immature mites, which indicates, that due to the
excellent breeding conditions, almost all ticks fertilize and survive, even in
the brood of worker bees. This is why there is a surge in the size of the tick
population in June and July, which you will see if you will use alcohol wash of
the mites from worker bees + brood control, as a main control method. This
measurement will give you as a result, the state of the mites' population on
the day of control, but with not very high reliability, since you cannot check
all the bees and the whole brood. After collecting the material, you have to
use mathematical prediction method...
Thanks
to the same process, a powerful increase of the "mites drop" occurs
in August-September and October, when after 2.5-3 months, ends the life course
of the most mass summer generation of the mites born in May, June and early
July. If you will use the control method based on counting the "mites
drop", then you can get almost 100% reliable results with a delay of 2.5-3
months, that is, with the interval, equal to the average life length of the
mites. If you want to find out data on
the size of the mites' population at the time of control, then you will have to
use the latest data on the state of the mites' population three months ago, and
also use mathematical prediction. We use this method and it is quite accurate.
You can read about it in our previously published work.
So,
in fact, we once again substantiated the correctness of our application of the
two-graph method for assessing the state of the mites' population, which is based on separate
accounting of the mature female mites and of young immature female mites,
in the overall amount of the mites
falling on the sticky board.
In
addition, we have shown, that you cannot take into account the entire
"mite's drop", if you want to
use it as an indicator of the need to use chemical drugs. In this case, it is
necessary to take into account only mature dark mites.
The
fall of a young immature mites, on the contrary, indicates the moment, when the
conditions for the development of the mites' population are the worst. It is at
such moments it is possible using the minimal amount of acaricidal drugs to
achieve maximum death of the mites and to reduce the size of their population,
minimally injuring the bees of the family.
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