Serjio Glebskij
Independent research project Apivox
Email - glebskij@gmail.com.
Key words - oxalic acid, Varroa mites, acoustic control
Annotation
Oxalic acid is a very effective active substance against Varroa mites if
applied in the absence of brood and with sufficient humidity in the hive. It
does not yet cause resistance in mites, but it also has a certain effect on
bees [1]. But the mechanism of its effect has not been comprehensively tested.
There is scientific evidence that:
• The most effective is the use of 3.2-3.7%% oxalic acid, diluted in
sugar syrup 1:1 [2].
• After treatment with oxalic acid, the temperature in the hive
increases, even in the autumn broodless period, to temperatures of +33C-
• The use of oxalic acid can provoke the start of oviposition by the
queen, despite the late autumn time.
• Oxalic acid acts on Varroa mites even without contact with them [4].
Our experiments have shown that there is a direct relationship between
rising temperatures and the number and speed of mite shedding. Only where there
is a rise in temperature above +
This shows that mite shedding is the result of a complex of actions.
• Death from the direct effect of the acid itself and its vapors on
Varroa mites.
• Fall of the mites due to the high temperature to which bees heat up
when working with their wings.
• Fall of the mites due to mechanical vibration created by bees at high
speed of flapping their wings
• Death of the mites due to the fact that oxalic acid has an indirect
effect on mites through the hemolymph and fat body of the bee, which partially
metabolizes oxalic acid, and which in this way enters the body of mites [6].
All together creates a set of conditions for the death and subsequent fall of Varroa mites when bees are treated with oxalic acid.
Introduction
There are several ways to treat bees with oxalic acid - spraying with an
aqueous solution of acid, drip treatment with a solution of acid in glycerin,
drip treatment with a solution of acid in sugar syrup and sublimation. The best
overall efficiency and safety indicators are for a 3% solution of oxalic acid
in sugar syrup 1:1. But what happens during the processing? What is the cause
of mites fall? It is believed that oxalic acid produces a contact effect. At
the same time, the effect of sugar-free solutions and sublimation is less
effective and lasts for less time. It is possible that sugar and glycerin
adsorb moisture from the air, and this is the reason for their effectiveness.
The aqueous solution directly supplies some water, which, however, quickly
evaporates, after which the acid can only act if the hive is sufficiently
humid. And this has been confirmed experimentally [1].
On the other hand, there is scientific evidence that the death of mites
also occurs in the closed volume of a laboratory capsule in which mites and
drops of corresponding liquid containing oxalic acid are placed [4]. The same
trend is observed. The best effect is obtained from a solution of oxalic acid
in glycerin and then in sugar syrup. Thus, it can be argued that oxalic acid
produces not only a contact effect on Varroa mites, but also a general
poisoning effect.
But this is not the only way oxalic acid enters the body of mites. This is confirmed by scientific data [5]. A preparation of oxalic acid, labeled with radionuclides, was introduced into the bee colony using the usual method - that is, drip. As a result, after some time, radionuclides from a solution of oxalic acid were discovered in the body of bees and their hemolymph. Radionuclides were detected in 8-9 day old brood. Radioactive markers were also found in the wax of freshly built honeycombs and in fresh honey. At the same time, the maximum infestation of bees was during the first 4 days after using the drug. According to scientists, this may mean that the results of the experiment are consistent with the hypothesis of the metabolism of oxalic acid carried out by bees. Thus, oxalic acid can act on mites in the same way through feeding on adult bees and even brood, leading to their death.
But what happens to the bees in the hive after they are treated with oxalic acid? We conducted an experiment with four families of different strengths.
Materials and methods
For the experiment, we used four families of third-generation Buckfast
bees. Two families were quite strong, each occupying a full hive of Dadan - No.
4 and No. 5, one occupied about 2 frames - No. 6, and the other 5-6 frames -
No. 3. The volume of the hives of all four
colonies was not reduced. (Figure 1).
Figure 1 - hives of the
families participating in the experiment
All families were left without any treatment throughout the entire spring-summer season of 2023. Since April, mite control was carried out in them, which by September 19 amounted to the following values: No. 3 - 2.5%, No. 4 - 19%, No. 5 - 14.4%, No. 6 - 14.5%. The remaining sealed brood available on September 19 was removed. For processing, dehydrated oxalic acid was used, which was diluted to a concentration of 3% in sugar syrup with a concentration of 1:1. The treatment was carried out dropwise, at the rate of 5-6 milliliters of the composition for each frame occupied by bees. To monitor the effectiveness of the treatment, observation of mites falling onto a sticky board was used. After treatment, the temperature in the hives was measured using digital thermometers with a remote sensor placed between the frames occupied by bees, in the center of the hive at a height of approximately the middle of the frame. Acoustic monitoring was carried out using the Apivox Smart Monitor device (apivox-smart-monitor.weebly.com).
Results
The first treatment was carried out with oxalic acid, diluted to a
concentration of 2.5% in sugar syrup with a 1:1 consistency. After 4 hours,
hardware control began, which gave the following results (Figure 2). As a
result, in hives No. 4 and No. 5 powerful signals were recorded in the range of
240-260 Hz, significantly exceeding all other sounds in the hive, which was
indicated by the red color of the graph in the upper half of the screen.
Moreover, it was in these hives that a significant rise in temperature was
observed to +
Figure 2 - results of acoustic and temperature control
Five days after treating the colonies with oxalic acid, all hives were
inspected. Firstly, due to the presence of a signal in the frequency range
240-260 Hz, which corresponds to signals associated, in our opinion, with the
care on open brood (aeration, heating), we monitored the frames between which
sensors were installed in hives No. 4 and No. 5. It turned out that in both
hives the sensors were located between the frames with honey, and there was no
brood. This means that the sound signals only coincided in range with the
signals of caring for open brood, but the task and reason for the work
performed by the bees was completely different. The sticky boards were also
checked for the presence of mites that died after treatment. The result
coincided with the distribution of temperatures and sound signals recorded on
the day of treatment. In hives No. 4 and No. 5, the shedding was quite
significant, and according to estimates, it was 600-800 mites in each hive.
About 10-15 mites fell in hive No. 3 and 2-3 mites fell in hive No. 6. On the
same day, colonies in hives No. 3 and No.
Figure 3 is the result of
acoustic control of experimental colonies
The figure shows that the family in hive No. 3 responded to the
treatment with the appearance of a sound signal in the range of 240-260 Hz at
17-52, and by 19-21 this signal became predominant in the hive. Hives No. 4 and
No. 5 were not treated again, but by the evening they also had sound signals in
the specified frequency range, which most likely indicates the continued effect
of oxalic acid on bees. Hive No. 6 again did not respond to repeated treatment
with the appearance of a specific sound signal. After another six days, another
personal control of all hives that were treated with oxalic acid was carried
out. During the control, the maximum fall of mites was again recorded in hives
No. 4 and No. 5. This time quite a lot of mites fell in hive No. 6. Acoustic
monitoring showed that the process of exposure to oxalic acid on bees
continued. In addition, the presence of nest heating signals could indicate
preparation for brood rearing. After another three days, repeated control of
mites drop on the sticky board was carried out. An examination showed that in
hive No. 3 fell only a few mites; in
hive No. 4 and No. 5 it was quite large, but we are talking about several
dozen. The next control was carried out after another 10 days. Monitoring the
mites drop on the sticky board showed that the fall continues at approximately
the same rate as before. An examination of the families showed the presence of
brood in the weakest families No. 3 and No. 6. This brood was completely
unexpected, since all the frames with the sealed brood had previously been
destroyed. This may mean that this is a new brood that appeared in the period
after the first treatment of colonies with oxalic acid around September
It should be added that we observed a similar reaction in families in
another apiary in mid-November at positive external temperatures (Figure 4).
Figure 4 - brood in
mid-November after treatment with oxalic acid
The next control of families was carried out after another 10 days. The
mites drop was approximately the same as the previous time - several dozen
mites in hives No. 4 and No. 5, and a single mites in hives No. 3 and No.
(VERY IMPORTANT: In real beekeeping practice, repeated treatments cannot
be carried out due to the subsequent significant loss of bees! Colonies, after
repeated treatment, are greatly weakened until their complete death (Figure 5).
Figure 5 - bees that died
after repeated treatment of the colony with oxalic acid
As a rule, treatments of the same bees are not carried out.
Overwintering colonies of bees are processed in winter or late autumn at
temperatures from
Acoustic control of these families showed that family No. 4 again
responded very actively to the treatment, generating sound signals in the range
of 240-260 Hz. (Figure 6).
Figure 6 – results of acoustic control of families No. 4 and No. 5
At the same time, it was noted during observation in the Monitoring
mode, that the signals in the region of 240-260 Hz. had a characteristic
appearance, indicating that the frequency in the range of 240-260Hz. was the main
frequency of the signal emitted by the bees (Figure 7).
Figure 7 - spectrum of bees
sounds during acoustic control of colony No. 4
Discussion
The results of the experiment confirmed that the method of treatment
with oxalic acid diluted in sugar syrup turned out to be quite effective and
efficient. Inspection of sticky boards in experimental hives confirmed that
maximum mites drop occurs in the first 5-6 days. This is consistent with the
results of scientific studies, which say that it is during this time fall up to
90% of the total number of mites that will die as a result of treatment.
(Figure 8)
Figure 8 - graph of mites fall
after treatment with oxalic acid in different variants. From work [1].
It is true that with such a treatment the temperature in the hives
actually rises quite strongly, up to +35-
Figure 9 - graph of
temperature changes in hives of families treated with oxalic acid. From work
[3].
In addition, in this experiment, a completely new and previously unknown
fact was fixated - the reaction of bee families to treatment with oxalic acid,
in the form of the appearance of a certain characteristic sound and at the same
time a fairly strong rise in temperature. In full-fledged families which
occupied a full hive, was fixated an intermittent sound at the main frequency
of 240-260 Hz., which was found out thanks to specific spectrum diagram (Figure
10).
Figure 10 - graph of the
spectrum of a pulse sequence filled with a carrier frequency and the spectrum
of acoustic signals in full-fledged colonies of bees of the apiary, after
treatment with oxalic acid.
The same sounds with the same spectrum figure are observed before
swarming and when the queen is lost. We consider these sounds to be signs of
"open brood care." This sound is emitted by the bees on combs with
brood, periodically opening their wings and making sounds with them for a
fairly short interval of time. These sounds are repeated by different bees at
irregular intervals (Figure 11). As a result, an intermittent signal with a
specific spectrum pattern appears.
Figure 11 - The bee on comb
with brood actively flapping her wings
We believe that a possible reason for the appearance of such a signal when bees are treated with oxalic acid is the possible similarity of the smell of oxalic acid and the smell of open brood. It is known from scientific works that open brood secretes several types of acids [6]. In particular, the larvae of worker bees secrete acids - isobutanoic, isovaleric, nonanoic, fumaric, benzoic, phenylacetic, myristic, suberic and azelaic. This could explain the reason why bees perform actions similar to aerating and warming of open brood. In this case, the bees, starting to work with their wings, raise temperature so much that conditions favorable for the laying of eggs by the queen are created. It is this effect that leads to what beekeepers who use oxalic acid for autumn treatments talk about - to the beginning of egg laying by queens at the most inappropriate autumn and winter time! A completely different situation develops in weak colonies that are in a full hive and are not separated from the main volume of the hive by an insulating partition. Such colonies, as we saw in our experiment, are not able to raise the temperature in all hive. But they can make this between two frames. We saw that the smallest families were the first to rear brood after treatment. At the same time, we also observed that the effect of acid on Varroa mites was significantly weaker in such families. The mites drop was also significantly smaller.
An additional factor in the effect of oxalic acid on mites could be its metabolization by bees. It is possible that part of the sweet liquid with acid falls on the bees during processing and, voluntarily or involuntarily, enters their body when they are cleansed of it, because according to the instructions, you need to drip syrup with acid specifically on the bees between the frames. Once on the bees and, possibly, in their food tract, oxalic acid enters their hemolymph and fat body, which the mites feed on. Thus, the acid not only has a contact effect on Varroa mites, but also directly enters their body, weakening or killing them. And such a factor may be the reason for the long fall of mites after exposure to oxalic acid. After all, as we showed earlier, mite fall can occur quite actively up to three weeks after treatment.
At the same time, the hard work performed by the bees with their wings
is sometimes sufficient to raise the temperature in the hive to +40-
Conclusion
Thus, we can say that the result of treating bees with oxalic acid is a combination of factors that have a detrimental effect on Varroa mites. Namely:
• Contact effect of oxalic acid on bees and mites.
• Vibration from the active work of bees with their wings as a result of
exposure to oxalic acid, leading to better shedding of mites.
• A sharp rise in the bees' body temperature, leading to the activation
of mites, their movement throughout the bee's body, and better abscission.
• A sharp rise in temperature to values above +
• Additional effects of acid on mites through the hemolymph and fat body
of bees.
• General toxic effect on mites through breathing acid vapors. (Including the same effect, although to a lesser extent, on bees.)
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