Abstract

The objective of this research was to determine the chemical composition, evaluate toxicity and acaricidal effect of essential oil of Eucalyptus robusta to control Varroa destructor of bees. Essential oilof Eucalyptus robusta (E. robusta) was extracted from fresh leaves by steam distillation using a Clevenger apparatus and was analysed by chromatography in gas phase coupled with mass spectrometry GC - MS, With an Agilent CGMSD Technology. The brine shrimp lethality test (BSLT) was used to evaluate the toxicity of the oil; the modified method of McLaughlin et al was employed in this study. The acaricidal features of the essential oil was evaluated usingbee hives infected by Varroa destructor, the method followed is the biological method "covers background". Results were analyzed by ANOVA followed by the post hoc tests.Fresh leaves of E. robusta by steam distillation yielded 0.83 % (v/w) of essential oil. Investigation of the oil onGC/MS resulted in the identification of 15 compounds, the most abundant constituent was 1,8-cineole (65,97 %), other notable compounds include p-cymene (7,83%), o-cymene (4,75%), Tetracosane (4,20%), alpha-pinene (1,89%) and 1-phellandrene (1,52 %) were also among the constituents identified. The acaricidal features of the essential oil was evaluated usingbee hives infected by Varroa destructor,a significant effect of oil was observed (p< 0.05). Cytotoxic effect was assayed using the brine shrimp lethality test, Probit’s analysis of the result revealed an LC50 value of 9, 42 μg/ml. Essential oil extracted from E. robusta showed the presence of 1,8- cineole coupled with high cytotoxic and acaricidal effects suggest it may not be suitable for medicinal purposes but can be used as insecticidal agents. Keywords: Eucalyptus robusta; leaf essential oil; toxicity; Chemical composition; Varroa destructor.

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