Study of effectiveness of lactic acid at varroatosis in the apiaries of Tyumen region, Russia

The study objective is to study the effectiveness of lactic acid in varroatosis and its impact on the development of bee colonies under conditions of the South of Tyumen region. The acaricidal effectiveness of lactic acid was studied in October 2019 using one method in two experiments in 30 broodless bee colonies kept in two apiaries, where bee colonies were divided into 2 groups (experimental 10 colonies and control groups of 5 colonies each). For treatment of bee colonies from the experimental group, frames with bees were removed from the hives in turn, which were sprayed with a 15.0% aqueous solution of lactic acid in the volume of 5 ml on each side of the honeycomb. Bee colonies were treated twice with an interval of 5 days. The bees in the control group were not treated. Dead mites were registered on a daily basis in all groups within 5 days after each treatment, for these reasons laminated cardboard sheets were placed on the bottom of the hives, which then were taken out and the number of fallen ectoparasites was recorded. Studies on the impact of lactic acid on the development of bee colonies were conducted in 20 brood bee colonies in the period from May to July 2020. It has been found that the effectiveness of treatment of experimental bee colonies with the drug was 90.0±2.1% (apiary No 1) and 7.8±1.9% (apiary No 2). At the same time, the maximum death of mites in colonies was observed during the first day after treatment. In the control groups, the number of mites decreased by 10.9±0.8% and 11.6±1.0%, respectively. It has been established that the treatment of bees with an aqueous solution of lactic acid in the above concentration, dose and multiplicity did not have a negative impact on the development of bee colonies, their strength and food supply, and no deaths of bees and queens were detected during the observation period.


Introduction
Diseases and pests of bees have harmful effect on the world beekeeping. The pathogenic agent of varroatosis, the mite Varroa destructor, is a vector of many pathogens of bacterial, viral and fungal infections, by contributing to mixed infections and infestations and the death of bee colonies around the world (Fig. 1). The widespread use of medicines based on pyrethroids, organophosphates, and formamidines for the treatment of bee colonies against varroatosis has led to the fact that mites have evolved resistance to most acaricides containing amitraz,

Materials and methods
The effectiveness of lactic acid for treating bee colonies against varroatosis was studied in two experiments using one method in October 2019 on 30 broodless bee colonies of two apiaries located in Tyumensky District (Fig. 2). Bees were kept in 12-frame hives with removable bottom board. Colonies strength averaged 10.0±0.5 frames. During the study period, the average air temperature was 5.9-14.6 °C, the daytime temperature -7.3-19.0 °С and the night temperature -7.0-14.3 °С. In both experiments, bee colonies were divided into 2 groups (experimental -10 colonies and control group of 5 colonies each). For treatment of bee colonies from the experimental group, frames with bees were removed from the hives in turn, which were sprayed with a 15.0% aqueous solution of lactic acid in the volume of 5 ml on each side of the honeycomb (Fig. 3). Bee colonies were treated twice with an interval of 5 days. The bees in the control group were not treated. Dead mites were registered on a daily basis in all groups within 5 days after each treatment, for these reasons laminated cardboard sheets were placed on the bottom of the hives, which then were taken out and the number of fallen ectoparasites was recorded. After that, the experimental and control colonies were treated twice with bipin (12.5% amitraz emulsion concentrate) according to the instructions for use. The effectiveness of treatment was determined according to the formula: The number of dead mites after treatment with lactic acid Effectiveness of lactic acid,% The number of dead mites after treatment with lactic acid and bipin  To conduct study of effect of lactic acid on the development of bee colonies, in May 2020, 20 bee colonies were selected, which were divided into two groups -an experimental and a control group of 10 colonies each. Bee colonies were kept in 16-frame hives. Groups were formed by analogy, taking into account the age of queens, the colonies strength, food supply, and low (<1.0%) infestation with Varroa destructor mites. Bee colonies from the experimental group were treated with 15.0% lactic acid solution by removing from the hives and spraying bee frames in a volume of 5 ml on each side of the honeycomb twice at intervals of 5 days. Control colonies were not treated. For three months after treatment, all bee colonies were controlled every 2 weeks, the number of bee frames was taken into account, and the number of sealed brood was determined using a framegrid with squares of 25 cm 2 , including 100 bee cells. Frames with honey and beebread were weighed. The results of all experiments were analyzed using the One-Way ANOVA.

Results and Discussion
The study found that double treatment (at 5 days intervals) of broodless bee colonies with 15.0% aqueous solution of lactic acid by spraying frames with bees in the volume of 5 ml on each side of the honeycomb reduced the number of Varroa mites by 90.0±2.1% (94.1-86.3%, apiary No 1) and 87.8±1.9% (89.9-84.8%, apiary No 2), respectively. At the same time, the maximum death of mites in colonies was observed during the first day after treatment. In the control group (apiary No 1), mite mortality during the observation period corresponded to 10.9±0.8% and in apiary No 2 -11.6±1.0%. The results of the study are presented in tables 1 and 2. Ukrainian Journal of Ecology, 10(5), 2020  The results showed that there is no negative impact of lactic acid on the development of bee colonies. During the experiment, no dead queens and bees were recorded in both groups.
In Russia, the studies of acaricidal activity of lactic acid were carried with the use of a 10% aqueous solution of the drug by spraying combs with bees in brood colonies, while the effectiveness of treatments ranged from 63.7±1.2% to 80.1±1.9% (Lugansky et al., 1987). No information on the effectiveness of lactic acid in the treatment of broodless bee colonies against the varroatosis in apiaries has been found in Russian Federation. The scientific findings covered in the materials of German and Swedish scientists demonstrate a high (94.2%-99.8%) acaricidal effectiveness of lactic acid in the treatment of broodless bee colonies and swarms (Kraus & Berg, 1994;Wallner & Fries, 2003;Rosenkranz et al., 2010). According to Colin M.E (1997), in the Mediterranean regions, treatment of bee colonies in the broodless period by spraying frames with bees, at a dose of 5-8 ml of 15% lactic acid on each side of the comb, reduced the number of Varroa mites to 80%. In order to maintain a low level of infestation of bee colonies with varroatosis, bee colonies should be treated four times a year with this drug. According to the Ministry of Agriculture and Forestry of New Zealand (2001), double use of an aqueous solution of lactic acid in autumn in the above concentration by spraying combs with bees in a volume of 5-6 ml on each side causes the death of Varroa mites from 83 to 99%, which coincides with the results of our studies, where in some colonies the death rate of Varroa mites reached 84.8-94.1% after treatment with the drug. Our experimental data are also consistent with the results obtained in Turkey by Ahmet Onur Girişgin and Levent Aydin (2010), who treated bee colonies with 15% lactic acid solution in the autumn period by spraying frames with bees three times with an interval of 7 days in the volume of 5 ml on each side. The effectiveness of treatment was 87.7%, while the researchers did not observe a reduction in egg-laying of the queen bee and the death of adult bees, which is also confirmed by the results of our study. Thus, our experimental data correspond to the results of studies of other authors. We consider it necessary to continue study aimed at obtaining objective data on the effectiveness of the drug and its environmental safety for bees and bee products with a view to further use the lactic acid for the treatment of bees against varroatosis in small apiaries of Tyumen region and other regions of Russia.

Conclusion
The study found that under conditions of the South of Tyumen region double treatment (at 5 days intervals) of broodless bee colonies against varroatosis with 15.0% aqueous solution of lactic acid by spraying frames with bees in the volume of 5 ml on each side of the honeycomb reduces the number of Varroa mites by 90.0±2.1% (apiary No 1) and 87.8±1.9% (apiary No 2), respectively. At the same time, the maximum death of mites in colonies was observed during the first day after treatment. It has been established that the treatment of bees with an aqueous solution of lactic acid in the above concentration, dose and multiplicity does not have a negative impact on the development of bee colonies, their strength and food supply, and no deaths of bees and queens were detected during the observation period.