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

Abstract

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%), α-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 μg/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.

Evaluation of the Essential Oils Used in the Production of Biopesticides: Assessing Their Toxicity toward Both Arthropod Target Species and Beneficial Pollinators

“…In this case, there was a 71.06% mortality rate in Varroa mites and a 12% mortality rate in A. mellifera after a 10 h exposure period to 5.5 µL/L air [78]. However, a high content of 1,8-cineole increased the toxicity of the volatile oil not only in insects but also in other organisms, such as shrimps (Artemia salina (L.) (Crustacea: Artemiidae) [130], rats [131], etc. The oil is extracted from the leaves of Melaleuca alternifolia (Maiden & Betche) Cheel (Myrtaceae); the tea tree is a small tree native to Australia [132].…”

Acaricidal Toxicity of Four Essential Oils, Their Predominant Constituents, Their Mixtures against Varroa Mite, and Their Selectivity to Honey Bees (Apis cerana and A. mellifera)

“…E. globulus and R. officinalis oils, dominated by 1,8-cineole, had low toxicity against V. destructor compared to previous studies [63,64]. However, the toxicity of 1,8-cineole, an inhibitor of AChE, varies depending on the target pests, as has been shown in different studies [27,[65][66][67].…”

Eucalpytus: An Underestimated Versatile Species

“…The same result was found in the species E. robusta and E. sideroxylon which exhibited a strong acaricidal effect on Varroa and a chemical composition rich in 1,8-cineole, with respective percentages of 65.79% and 40.24%. Thymol is a product whose efficacy in the control of mites is established and that this effect could be potentiated by combining it with local Eucalyptus essential oils (Atmani-Merabet et al, 2020). Eucalyptus essential oil is shown to exhibit octopaminergic agonist activity (Rattan, 2010).…”