In Vitro Activity of Several Essential Oils Extracted from Aromatic Plants against Ascosphaera apis.

Michelina Pusceddu,Alberto Angioni,Ignazio Floris,Nicoletta P Mangia,Alberto Satta

doi:10.3390/vetsci8050080

Michelina Pusceddu, Alberto Angioni + Show 3 more

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https://doi.org/10.3390/vetsci8050080

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Abstract

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.

Highlights

All the identified species of fungi belonging to the genus Ascosphaera (Ascomycota: Plectomycetes; Ascosphaearales) have been detected in bees [1,2]
Among the 10 pure essential oils tested against A. apis using the paper disc agar diffusion (PDD) method, the most effective were T. herba-barona and T. capitatus, which fully blocked the growth of the fungus (Table 1)
The assays on the vegetative forms performed in Sabouraud broth showed an inhibitory effect (MIC) on the growth of A. apis at 100 ppm for T. capitatus and T. herba-barona oils and 200 ppm for Cinnamomum oil, whereas Helichrysum did not show any inhibitory activity even at the highest concentration (500 ppm) (Table 2)

Summary

Introduction

All the identified species of fungi belonging to the genus Ascosphaera (Ascomycota: Plectomycetes; Ascosphaearales) have been detected in bees [1,2]. Bee larvae in the fifth instar are the most sensitive to the disease, as they have favorable environmental conditions in their gut for spore germination [6,7,8]. Once in the larval gut, the spores are activated by CO2 obtained from the cells [9]. They can germinate in the lumen, producing a mycelium which pierces the larval cuticle [9]. In this phase, the larvae look like tiny pieces of chalk or “mummies”, which gives the name of chalkbrood to the disease [7,10]. The larvae become mummified, changing from white to a dark gray or black color due to the presence of spores on the larval cuticle [10,11]

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