Essential oils with the potential for varroa mite control (Varroa destructor) : mechanisms of toxicity and negative impact on honey bee (Apis mellifera)
The parasitic bee mite varroa (Varroa destructor) is among the most serious honey bee pests. Beekeepers utilize a wide range of different synthetic acaricides to keep mite populations under control. However, due to documented adverse impact of synthetic substances, the use of naturally derived acaricides, among these essential oils, is greatly being promoted. Tymol is already used in beekeeping. We present a review of the existing knowledge regarding the effects of essential oils with known acaricide actions on honey bees Apis mellifera. In particularly, we focus on the mechanisms of toxic action on the immune and nervous systems. We conclude that due to their mechanisms of toxicity several essential oils could be used for varroa mite control, still very little data regarding the negative effects of essential oils on honey bees are known. In particular, knowing their interferences with the immune response is important to be able to predict the potential effect on the colony health. The majority of toxicity data currently exist for thymol and its commercial preparations under acute exposure (Apiguard©, Api Life VAR©), but the data for a number of other potential acaricide-related essential oils are missing. We recognize the need for systematic screening of potential toxicity and sublethal effects of essential oils with acaricide action on honey bees. Standardised application of essential oils in honey bee keeping remains a challenging task for the future.