Acaricidal and antiacetylcholinesterase activities of essential oils from six plants growing in Egypt

Abstract

ABSTRACTEssential oils from six plant species that occur in the north part of Alexandria governorate, Egypt, were extracted by hydrodistillation in a Clevenger-type device. The chemical compositions of the essential oils were analysed using gas chromatography-mass spectrometry. The essential oils were tested for their toxicities towards the adults of Tetranychus urticae by contact and fumigant methods. The essential oils were also tested for their inhibitory effects on acetylcholinesterase of T. urticae adults. The results of GC-MS analysis showed that monoterpenes were the dominant class of compounds in all essential oils. The compounds 1,8-cineole (71.77%), limonene (74.29%), pulegone (77.45%), α-pinene (35.49%), β-citronellol (35.92%) and terpinen-4-ol (20.29%) were the major components of the essential oils from Calistemon viminals, Citrus paradisi, Origanum vulgare, and Thuja orientalis, and Cupressus macrocarpa, respectively. The acaricidal activities against T. urticae varied depending on the assay method employed, tested essential oil and exposure time. In general, the essential oils were more toxic to T. urticae using fumigation method than contact method. Also, the contact toxicity was higher after 48 h of treatment than 24 h. The essential oil of C. macrocarpa (LC50 = 5.69 mg/L air) caused the highest fumigant toxicity, while the essential oil of O. vulgare (LC50 = 67.89 mg/L) was the most effective in contact toxicity. In addition, the tested essential oils showed remarkable inhibition on the activity of T. urticae AChE indicating that the mortality of the mite may be attributed to the inhibition of AChE. Based on the results of the current study, it can be noticed that the tested essential oils possess a potential to be used as alternatives for synthetic pesticides for controlling T. urticae.