Comparison of Alternative Application Methods for Anti-Varroa Lithium Chloride Treatments

SIMPLE SUMMARY: The Varroa mite is one of the most dangerous pests of honey bee colonies, spreading many diseases, and its high infestation rate leads to the death of the colony. Due to its wide-scale distribution and lethal effect, this mite parasite threatens not only the honey industry but also the pollination of many plant species, including several cultivated plants. Therefore, an uncontrolled varroosis could threaten the human food supply as well as trigger biodiversity loss. Control options against Varroa are still inadequate; the mite could develop resistance to synthetic chemicals, whereas the efficiency of organic acid and essential oils-based treatments is very variable. Recently, lithium has been identified as a potential and effective anti-Varroa agent with both systematic and contact modes of action. Present experiments revealed that the efficiency of the lithium treatment depends greatly on the application method. The trickling method of application in repeated treatment and concentration of 500 mM provided very high, >>90%, efficiency. However, further investigations are required before the lithium chloride could be registered as a veterinary medicine in beekeeping practice. ABSTRACT: Varroosis is one of the most dangerous threats to the bee industry but means of its treatment are still unsatisfactory. Lithium-based anti-Varroa treatments may provide an alternative, as this trace element can be a natural component of honey and is well tolerated by adult bees. However, it can be toxic to larvae and its use in beekeeping practice is not yet well understood. The present study aimed to investigate the efficacy of relevant application methods of acaricides used in beekeeping practice in brood-free conditions for lithium. Vaporisation proved to be an inefficient method of lithium treatment and killed only 9.9 ± 3.3% (mean ± SD) of mites in the hive. Lithium-impregnated paper strips showed moderate efficiency by killing 55.1 ± 26.2% of mites. The most effective way of applying lithium was the trickling method; different trickling treatments decreased the abundance of mites on average by 65 to 99.7%, depending on the applied dosage and the number of treatments. Repeated trickling treatments were more effective than single treatments, and they generally provided >90% efficiency. Experiments also proved that adding sugar to the trickling solution does not influence treatment efficiency. Thus, it is suggested that repeated and sugar-free trickling treatments with moderate lithium dosage could be the most rational methodology. Since lithium is not yet legalised in beekeeping practice, comprehensive studies are also needed to uncover the amount of lithium residue in bee products, depending on the treatment parameters.