Praca oryginalna Original paper
Varroa destructor is a dangerous parasite because honey bee colonies infested with the mite die out within 3-4 years (13, 39). This is due to the fact that V. destructor exerts its adverse effect on bees in many different ways.
When feeding on bees or brood, mites use their mouthparts to puncture the lining of the host’s body. The wounds become an entrance for numerous patho-gens present on the body of brood or on bees (15) as well as those transmitted by V. destructor (2, 16, 17, 28, 29, 33, 42). According to some authors V. destructor contributes to such honey bee conditions as American foulbrood and chalk brood (42). It has been proved that it promotes the development of acute bee paralysis (1). Martin et al. (24) discovered that the presence of V. destructor in diseased colonies is accompanied by the following viruses: deformed wing virus (DWV) and slow paralysis virus (SPV).
Infestation with the mite leads to quantitative and qualitative changes in hemolymph. Weinberg and Madel (44) report that 1-3 mites feeding on a worker bee pupa cause a reduction in the host’s hemolymph volume by 23.6%; in the case of a drone pupa, the volume of hemolymph decreases by 18.2%, on average.
An attack of the mite brings about changes in the level and composition of proteins (41), which results not only from hemolymph loss but also from the effect
of substances excreted by V. destructor. The substances damage some hemolymph proteins (17) or hinder protein synthesis in the fat body (18). In broods, the activity of lisozyme drops by 30-40% as compared to its congenital level (18).
In order to prevent such a destructive effect of the mite on honey bees and broods, and consequently also on the whole colony, it is necessary to control the mite regularly every year. Abandoning anti-Varroa proce-dures in one season may have a negative effect on the condition of the whole apiary and its productivity in subsequent years even when anti-Varroa procedures are taken up again (5). Presently, no medications for varroosis show 100% efficiency. Besides, even if colo-nies are successfully cured of the mite in a short time they are usually re-infested by mites from neighboring apiaries not simultaneously treated for varroosis (38). However, carrying out yearly anti-Varroa procedures makes it possible to control the mite population at a level harmless to the bee colony.
Medications used in the treatment of varroosis are based on acaricides and essential oils. Presently, among the preparations registered in Poland are such medications as: Apiwarol, Biowar 500, Bayvarol, and Api Life Var. The first three preparations are chemo-therapeutic agents containing amitraz and flumethrin as active substances. Some residues of these substances may be found in bee products (3, 4); therefore it is recommended to use them not earlier than after the last honey harvest.
Efficiency of Varroa destructor management
with medications used in Poland*
)
BEATA BĄK, JERZY WILDE, MACIEJ SIUDA Apiculture Division, Faculty of Animal Bioengineering,
University of Warmia and Mazury, ul. Słoneczna 48, 10-710 Olsztyn, Poland
Bąk B., Wilde J., Siuda M.
Efficiency of Varroa destructor management with medications used in Poland Summary
Despite a wide choice of methods for V. destructor control, beekeepers are still uncertain as to which one is the most effective. Does one anti-Varroa procedure a year suffice or is it better to strike the population of mites several times during the season? Or perhaps is it better to treat bee colonies relying on essential oils and organic acids? The aim of the assay was to show which method for V. destructor management is most effective.
The results of the investigations show that the applied treatment pattern significantly affects the efficiency of Varroa destructor management and the degree of bees’ infestation in spring. The best way to control Varroa destructor was determined to be integrated anti-Varroa treatment.
Keywords: Varroa control, integrated parasite management, amitraz, flumethrin, thymol formic acid, oxalic acid
*) The study supported by the Polish Ministry of Science and Higher Education, research project No. 520/N-COST/2009/0.
One of the ways to prevent the contamination of the environment of the hive by the residues of anti-Varroa preparations is using so called “soft” heavy chemistry, i.e. substances that do not contaminate bee products in a way that would be dangerous for people, and that are often naturally present in bee products yet in low concentrations (22, 30). Therefore, this kind of treat-ment can be called ecological. In this treattreat-ment, some essential oils and organic acids are used.
Essential oils are basic components of Api Life Var. It contains thymol, eucalyptus oil, menthol and cam-phor. Among the organic acids used in the treatment of varroosis are formic acid, oxalic acid and lactic acid.
An excellent way to control the parasite is also by a mechanical method based on removing capped brood infested with the mite from the colony, which most often refers to drone brood that female mites find more attractive (14, 34, 36, 43). In this method we can use combs naturally built by bees at the beginning of swarming, as well as work frames that beekeepers introduce to the hive at this time.
In order to enhance the efficiency of anti-Varroa procedures, Delaplane et al. (9), Rice et al. (32), Sammataro et al. (35) recommend the application of various methods at different times of the season, with the aim of minimizing heavy chemistry use. Such a technique of controlling V. destructor is called in-tegrated parasite management (IPM). A variant with only “soft” heavy chemistry can be used, rendering the anti-Varroa treatment ecological (40).
Despite such a wide choice of methods for V. destructor control, beekeepers are still uncertain as to which one is most effective. Does one anti-Varroa procedure a year suffice or is it better to strike the population of mites sev-eral times during the season, which, however, would entail extra costs. Or perhaps is it better to treat bee colonies by relying on essential oils and organic acids.
The aim of the assay was to compare the effectiveness of different methods of V. de-structor management based on the preparations available in Poland.
Material and methods In the assay we used 100 bee colonies not treated for varroosis, kept in multistory hives. Out of these bee colonies we randomly created 4 experimental groups (25 colonies in each),
differenti-ated according to the varroosis treatment pattern to be applied in the assay:
Group I (CH) – the main summer treatment only, with a use of heavy chemistry (Bayvarol, Biowar, Apilwarol); group II (IT) – integrated pest management against Varroa; group III (N) – controlling the mite with a use of light chemistry (es-sential oils and organic acids only); group IV (C) – control group, not treated for varroosis. During the whole experiment time the same bee colonies were used. For the needs of regen-erating fallen bee colonies, bee packets from the particular groups were created.
In the assay we used only preparations registered in Po-land, i.e.: Apiwarol – a preparation in a form of fumigating tablets, 1 tablet containing 12.5 mg of amitraz as an active substance (3 tablets/per season); Bayvarol – strips to be sus-pended in a hive, 1 strip containing 3.6 mg of flumethrin; Biowar – strips to be suspended in a hive, 1 strip containing 500 mg of amitraz; Api Life Var – a preparation in a form of vermiculite blocks containing essential oils: thymol (76 g/ 100 g), mint oil, eucalyptus oil and camphor.
Apart from the above-mentioned medications, we also used organic acids: formic and oxalic. All preparations were used in accordance with the manufacturer’s instructions. In the colonies treated with formic acid, 200 ml of 85% acid were evaporated with a use of a horizontal Nassenheider dispenser. The colonies treated with oxalic acid were sprayed with its 3.5% solution in 1:1 sugar syrup.
Varroosis treatment and the efficiency of anti-Varroa procedures. The tested preparations were used according to the pattern presented in Table 1. Directly before and after every anti-Varroa treatment, we collected bee samples in or-Tab. 1. Anti-Varroa treatment patterns in individual groups and experimental years, alongside the efficiency of anti-Varroa procedures
Assay year Group and number of colonies Supportive spring treatment (Mar.-May) Supportive spring- -summer treatment (May-Jul.) Main summer treatment (Aug.) Supportive autumn treatment (Oct.-Nov.) 2010 CH (25) Bayvarol97.23%
IT (25) Api Life Var100% removing drone brood 100%
Bayvarol
100% oxalic acid100%
N (25) Api Life Var89% Api Life Var89% oxalic acis98.61%
2011
CH (25) Biowar76.6%
IT (25) Api Life Var54.11% removing drone brood 96%
Biowar
58.7% oxalic acid98.61%
N (25) Api Life Var44.21% Api Life Var44.8% oxalic acid74.5%
2012
CH (25) Apiwarol94.1%
IT (25) Api Life Var76% removing drone brood 92%
formic acid
54.9% oxalic acid100%
N (25) Api Life Var84% formic acid53.4% oxalic acid85.7%
Explanations: CH – the main summer treatment only, with a use of heavy chemistry; IT – in-tegrated anti-Varrooa treatment; N – only natural ways of controlling the mite with the use of essential oils and organic acids
der to assess the degree of infestation (ID) with V. destructor (Tab. 4) and the efficiency of a given anti-Varroa procedure (Tab. 1). The bee samples were collected from combs with brood and contained about 300 bees. The number of mites was calculated by the flotation method.
To calculate the degree of infestation (ID), we used the following formula:
ID = PN/BN × 100,
where PN stands for the number of parasites, and BN – the number of bees in a sample.
On the basis of the achieved results, we calculated the efficiency of each anti-Varroa treatment (TE), using the fol-lowing formula: TE = 100-ID1 × 100/ID0, where ID0 stands for the degree of infestation in a tested sample before a given anti-Varroa treatment, and ID1 – the degree of infestation in the sample after the treatment.
The data collected in the assay were analyzed statisti-cally. The significance of differences among the groups was assessed using the analysis of variance (Fisher’s test) by the computer program “Statistica”.
Results
We observed a significant effect of the treatment
pat-tern (F2,210 = 10.47, p = 0.000) and the year of the assay
(F2,210 = 12.03, p = 0.000) on the efficiency of anti-Varroa treatment, and a significant interaction between those
factors (F4,210 = 2.56, p = 0.040).
The lowest efficiency of varroosis treatment (i.e. 74.5% and 76.6%) in a season was observed in groups CH and N, respectively, in year 2011. These values differed significantly from the efficiency achieved in groups IT in all experimental years, in group CH in 2010 and 2012, in group N and in 2010, where it ex-ceeded 94%.
During the whole test, on average the best results were achieved in group IT. The efficiency of the anti- -Varroa treatment pattern applied in this group reached 99.5%, which was significantly higher than in all other experimental groups (Tab. 2).
We also compared the average efficiency of the prepa-rations and anti-Varroa substances used in the assay. The highest average efficiency, i.e. over 92%, was observed in the case of Bayvarol, Biowar and oxalic acid. The significantly lowest average efficiency of anti-Varroa treatment, i.e. 68.1% and 54.2%, was achieved when using Biowar and formic acid, respectively (Tab. 3).
Table 4 shows average infestation degree before treatment, but only in colonies which wintered from the previous season. It was important for the authors of the experiment to show the influence of Varroa infestation in early spring. The results presented in table 4 do not include bee colonies which were created later to com-plete the number of colonies in a particular group. The lowest average infestation degree before treatment, i.e. 2.4% and 2.6%, was found in the bee colonies in which integrated treatment was applied and those treated with natural methods, respectively. The group in which only heavy chemistry was used manifested a higher average degree of infestation with parasites (3.8%), which was
similar to the infestation degree observed in the control group (3.0). This is because in group CH, the degree of bees’ infestation with the mite before treatment was checked only once during the season – in August, while in the remaining groups such tests were carried out in April. In 2010, bee colonies in the experimental apiary were significantly less infested by the mite than in the other experimental years. The average infestation de-gree in the apiary in 2010 was 2.1% (Tab. 4).
We observed a significant effect of the treatment
pattern (F2,299 = 135.99, p = 0.000) and the year of the
assay (F2,299 = 24.08, p = 0.000) on the degree of bees’
infestation with the mite after treatment, and a
signif-icant interaction between these factors (F6,299 = 2.56,
p = 0.040).
Tab. 2. Efficiency of anti-Varroa treatment in the years 2010- -2012 (in %) Year Group Years overall No CH No IT No N No 2010 25 97.2B 25 100.0Bc 25 98.6B 75 98.6B 2011 25 76.6Aa 25 98.6B 25 74.5Aa 75 83.1A 2012 25 94.1B 25 100.0Bc 25 85.6b 75 93.2B Groups overall 75 88.0A 75 99.5B 75 85.7A 225 91.2
Explanations: as in Tab. 1. Capital letters indicate significant diffe-rences between means at p < 0.01, lowercase letters – at p < 0.05
Tab. 3. Average efficiency of applied anti-Varroa medications (in %)
Preparation No Efficiency
% ± se
Api Life Var 177 71.7B ± 2.8
Apiwarol 25 94.1C ± 2.5 Bayvarol 50 98.8C ± 0.6 Biowar 50 68.1ABb ± 5.0 Formic acid 50 54.2Aa ± 5.9 Oxalic acid 150 92.8C ± 1.9 Overall 502 79.6 ± 1.5
Explanations: Capital letters indicate significant differences be-tween means at p < 0.01, lowercase letters – at p < 0.05
Tab. 4. Average degree of bees’ infestation with V. destructor before treatment in bee colonies, which wintered from the previous season from early spring in groups IT, N and C and from the beginning of August in group CH
Year Group No CH No IT No N No C 2010 23 2.6ab 23 1.2Aa 22 2.4ab 22 2.1ab 2011 25 4.8Bc 24 3.6ab 21 2.2ab 18 4.1B 2012 20 3.7ab 20 2.4ab 15 3.3ab 2 3.8bc Groups overall 68 3.8B 67 2.4A 58 2.6A 42 3.0B
Explanations: as in Tab. 1; C – control group. Capital letters indi-cate significant differences between means at p < 0.01, lowercase letters – at p < 0.05
The highest degree of infestation, i.e. 16.5% and 19.6%, was found in the control group in years 2011 and 2012, respectively, and it differed significantly from the results achieved in the remaining groups and years. Also the average degree of infestation in the three experimental years was significantly higher in group C than in the remaining groups and it reached 13.8%. In the groups in which anti-Varroa treatment was applied, the average degree of bees’ infestation with the mite did not exceed 0.6% and did not differ statistically (Tab. 5).
Discussion
The assay showed that the best anti-Varroa effects were achieved in group IT. This method made it possible to destroy almost 100% of the parasites. Also Delaplane et al. (9), Keith et al. (21), Rice et al. (32), Sammataro et al. (35) recommend using integrated treatment in the management of V. destructor, in the conviction that it is the most effective way of treating bee colonies suffering from varroosis.
Of all anti-Varroa preparations used in the assay, Apiwarol and Bayvarol showed the highest efficiency. The average efficiency of Apiwarol was 94.1%. For many years the preparation has been characterized by extremely high efficiency, often exceeding 90% (10), therefore it is particularly recommended to beekeepers.
The achieved average efficiency of Bayvarol was 98.8%. The results achieved in the discussed assay did not match with the results reported by Węgrzynowicz et al. (45) who found very little efficiency of this medica-tion, i.e. 42% and 45%, after an 8-week treatment with Bayvarol strips applied in two apiaries. The researchers observed at the same time that the efficiency of the treatment in individual colonies ranged significantly from 11 to 93%. In the discussed assay the efficiency of the medication in individual colonies was comparable.
Oxalic acid also showed very high efficiency (92.8%); however it should be remembered that it was used in the bee colonies that had been previously treated for varroosis during the season. The average efficiency of oxalic acid achieved in the discussed assay was a little lower than the efficiency observed by other researchers (19, 26, 27, 31, 40), in whose studies oxalic acid showed the efficiency of 97.29%-100%.
The efficiency of Biowar in the discussed assay appeared to be quite low, i.e. 68.1%. Field studies carried out by Chuda-Mickiewicz et al. (8) showed
higher efficiency of this preparation, i.e. 81.07-87.81%. Bieńkowska et al. (6) and Semkiw et al. (37) also achieved better results when treating bee colonies with Biowar. The efficiency of the therapy in their assay ranged between 75% and 90%.
Satisfactory anti-Varroa effects were achieved by eliminating drone brood. The efficiency of this proce-dure always exceeded 90%. Boot et al. (7) addition-ally used drone brood combs as traps to discover that 462 drone brood cells suffice to trap 95% of mites in a 1-kilogram colony during one day. Woyke (46) used bee brood combs as traps, which made it possible to destroy 97% of V. destructor females.
A solution that prevents an accumulation of anti-Var
-roa medication remains in the hive is using so called
“soft” heavy chemistry, i.e. substances that do not con-taminate bee products in a way that would be dangerous for people, and that are often naturally present in bee products, yet in low concentrations (22, 30). In this treatment some essential oils and organic acids are used.
In our assay we also used Api Life Var. The prepa-ration is recommended to be used in spring when the parasite is weak after winter. It can be also applied after the last honey collection as a procedure in the main anti- -Varroa treatment. Thymol contained in the medication partly affects the mites staying under caps, so the pres-ence of capped brood does not hinder the efficiency of the preparation to the extent that most chemotherapeutic agents do (25). The average efficiency of Api Life Var achieved in our assay was 71.7%, while its efficiency reported by Imdorf et al. (20) was 93.7% after a 4-week treatment, which increased to 97.7% after the next 4 weeks. Floris et al. (11) compared the efficiency of Api Life Var and Apiguard (a preparation with thymol in the form of a gel) to determine a higher efficiency of the latter medication. Apiguard destroyed 95.5% of parasites while Api Life Var only 81.3%.
It is worth remembering that to a high degree the efficiency of essential oils depends on environmental conditions, especially temperature, and it reaches 99% (12, 22, 23, 30). In the discussed assay, the efficiency of Api Life Var was noticeably different in the individual years of the test, and the lowest value was achieved in group N in year 2011 (ca. 44%).
In the discussed assay formic acid was administered with a use of a horizontal Nassenheider dispenser. In this way 200 ml of 85% formic acid were evaporated in each colony. The achieved average efficiency turned out to be surprisingly low, i.e. 54.2%. These results could be related to climate conditions, but the relationship was not observed. Skubida and Semkiw (40) used ca. 120 ml of 60% formic acid per colony and the same dispensers; their results were more satisfactory, with the efficiency of the procedure at the level of 73.7%.
Bee colonies from the group treated with heavy chemistry showed a higher degree of infestation with the parasite before treatment than other treated groups. The degree of infestation in CH was similar to that of the control group. This could have been caused by the fact
Tab. 5. Average degree of bees’ infestation with V. destructor after treatment Year Group No CH No IT No N No C 2010 25 0.2A 25 0.0A 25 0.1A 25 3.0A 2011 25 1.1A 25 0.1A 25 0.6A 25 16.5B 2012 25 0.2A 25 0.0A 25 0.1A 25 19.6B Groups overall 75 0.6A 75 0.02A 75 0.3A 75 13.8B
Explanations: as in Tab. 1; C – control group. Capital letters indi- cate significant differences between means at p < 0.01
that in group CH, the degree of bees’ infestation with the mite before treatment was checked only once during the season – in August, while in the remaining groups such tests were carried out in April. Nevertheless, as a result of anti-Varroa procedures carried out in this group, the degree of bees’ infestation with the mite dropped to a low level, i.e. < 0.7%.
Our essay indicates that various method of treatment
Varroa, not only IT, can prove to obtain a high (about
95% and higher) efficiency: in 2010 in group CH – 97.23%, in group N – 98.61%; in 2012 in group CH – 94.1%. The bee colonies not treated on Varroa died within the period of two or three years. Therefore the most important practice in V. destructor management is carrying out anti-Varroa procedures every year.
Conclusion
1. The applied treatment pattern, based on the methods available in Poland, significantly affects the efficiency of Varroa destructor management and the degree of bees’ infestation in spring.
2. The best way to control Varroa destructor is by using integrated anti-Varroa treatment.
3. Whatever treatment pattern is used in the colonies inflicted with varroosis, the degree of infestation after treatment is similar.
4. The assay results indicate that the most important practice in V. destructor management is consistently carrying out anti-Varroa procedures every year.
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Corresponding author: dr Beata Bąk, ul. Słoneczna 48, 10-710 Olsztyn; e-mail: beciabak@wp.pl
