In vitro activity of several essential oils extracted from aromatic plants against ascosphaera apis

The use of natural substances such as essentials oils against bee pathogens is of great interest as an alternative to traditional methods based on synthetic compounds like antibiotics and fungicides, in order to minimize the risk of having toxic residues in hive products and to prevent the development of resistance phenomena. This study evaluated the inhibitory, fungicidal and sporicidal activity of ten essential oils extracted from aromatic plants against Ascosphaera apis, the etiological agent of chalkbrood, an invasive honey bee mycosis. The most effective essential oils were Thymus herba-barona, Thymus capitatus and Cinnamomum zeylanicum, which showed values of minimum fungicidal concentration and minimum sporicidal concentration ranging from 200 to 400 ppm. Carvacrol was the main component of Thymus capitatus and Thymus herba-barona oils, whereas cinnamic aldehyde prevailed in Cinnamomum zeylanicum oil. Further in-apiary studies will allow the evaluation of side effects on bees and residues in hive products.