Chemical composition, toxicity, and acaricidal activity of Eucalyptus globulus essential oil from Algeria

The study was aimed at determining the chemical composition, toxicity effect and field varroacidal efficacy of the essential oil distilled from the leaf of Eucalyptus globulus (Eg) grown in Algeria. Brine shrimp lethality (BSL) assay and bee hives infected by Varroa destructor were used to assess the toxicity and acaricidal effect, respectively. Steam distillation of leaves yielded 0.93 % (v/w) of essential oil (EO). GC/MS Analysis revealed 39 compounds, essentially oxygenated monoterpenes (86.01%). The main constituents of the oil were 1,8-cineole (78.45 %), o-cymene (2.18 %), isopinocarveole (1.74 %), alpha-pinene (1.69 %), pinocarvone (1.34%) and veridiflorol (1.31%). The BSL assay revealed a highly toxic value of LC50 (67.55 mu g/mL). Furthermore, field efficacy testing on bee hives infected with Varroa destructor has confirmed the effectiveness of Eucalyptus globulus essential oil (EgEO) or thymol as varroacidal agents. Moreover, a EgEO + thymol association was more effective than EgEO or thymol alone. Finally, the use of EgEO + thymol may constitute a viable alternative to the thymol-based commercial treatment.