In vitro activity of essential oils from San Luis-Argentina against Ascosphaera apis

It can also be found in the literature that Calderone et al. (18) studied eight plant extracts. They were selected for evaluation of their potential to inhibit the growth of A. apis. Fungicidal activity of bay oil [Pimenta racemosa (Mill.) J.W. Moore], camphor, clove oil [Syzygium aromaticum (L.) Merr. et L.M. Perry], cinnamon oil (Cinnamomum species), citironellal, Spanish origanum oil (T. capitatus), [alpha]-terpinene, and thymol was assayed at four concentrations in agar media to determine their activity thresholds. Cinnamon oil (ex C. zeylanicum Blume) completely inhibited the growth of A. apis at 100 ppm for 168 h. Bay oil, citronellal, clove oil, origanum oil and thymol completely inhibited the growth at 1,000 ppm for 168 h. Camphor inhibited all growth at 10,000 ppm for 168 h, and [alpha]-terpinene inhibited all growth for 72 h at 10,000 ppm.

A previous study of the same H. latifolia oil used in our study showed that it had a high acaricidal effect against the destructive Varroa mite (11) a carrier of A. apis (19).

The monoterpenes and sesquiterpenes percentages of the oils from the species studied in this work are reported in Table III. The percentages were established taking into account the total of the identified compounds grouped in hydrocarbons and oxygenated compounds. The H. latifolia, L. juneliana and L. turbinata oils possessed a higher percentage of oxygenated compounds. The L. integrifolia oil contained a lower percentage of oxygenated compounds than the more effective species and a lower percentage of identified compounds: (76.2%), while the L. juneliana and L. turbinata oils contained a larger quantity of identified compounds (88.7% and 92.0%, respectively). The A. gratissima and L. integrifolia oils contained a higher percentage of oxygenated sesquiterpenes. The six studied oils that proved to have antifungal activity showed concentrations above the 30% of oxygenated terpenes.

Experiments carried out in vitro show that six of the oils tested possessed good fungicidal activity. As a result, we believe that they deserve to be tested in bee hives. However, an adequate way of application must be found to permit the successful reduction of fungal infection in bee colonies.

Acknowledgments

We would like to thank CONICET, ANPCyT for financial support on this research, as well as the Universidad Nacional de San Lius and Universidad Nacional de Mar del Plata.

References

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