Comparative study of two Eucalyptus species from Algeria: chemical composition, toxicity and acaricidal effect on Varroa destructor

Varroa destructor is an external parasitic mite that is a serious pest of honeybees and has caused severe losses of colonies worldwide. One of the feasible alternative treatments being used for their control is the application of essential oils, which are generally inexpensive and most pose few health risks. The investigation was designed to determine the chemical composition, toxicity and acaricidal effects of Eucalyptus amygdalina leaf essential oil (EaEO) grown in Algeria and to compare its activity on Varroa destructor with that of Eucalyptus globulus from the same region. Fresh leaves of E. amygdalina (Ea) by steam distillation yielded 0.77% (v/w), and investigation of the oil on GC/MS resulted in the identification of 35 compounds, with 1.8-cineole (35.78%) as most abundant constituent. Other notable compounds include spathulenol (12.58%), camphene (7.73%), a-pinene (4.38%), valencene (2.64%), while 2-carene and ledol (1.45%) were also among the constituents identified. The acaricidal features of the essential oil was evaluated using bee hives infected by Varroa destructor, and a significant effect of oil application was observed (p < 0.05). Cytotoxic effect was assayed using the brine shrimp lethality assay, Probit's analysis of the result revealed an LC50 value of 116.06 mu g/mL. Essential oil of E. amygdalina (EaEO) has potential acaricidal effect on Varroa destructor, but this effect is less important than the one recorded by E. globulus. Further studies are needed to determine the active component responsible for this effect.