Chemical Composition and Larvicidal Activity of Rosmarinus officinalis Essential Oil Against West Nile Vector Mosquito Culex pipiens (L.)

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Abstract
The dry aerial part of Rosmarinus officinalis, collected from Djebel Belkfif (Tébessa, North- Eastern, Algeria), were hydrodistilled in a Clevenger type apparatus and analyzed by GC and GC-MS. The larvicidal activity of the R. officinalis essential oil (EO) against the fourth instar larvae of Culex pipiens L. was determined after 24 hours of exposure according to the World Health Organization procedure. The R. officinalis EO effects, via application of two lethal concentrations (LC25 and LC50), were examined on morphometric parameters (weight and body volume) and main biochemical components (proteins, lipids, carbohydrates) at different exposure periods. Furthermore, glutathione-S-transferase (GST) activity and glutathione (GSH) rate were assessed as biomarkers of the detoxification system. The GC and GC-MS analysis led to the identification of 36 components representing 99.97 % of the total oil, in 1.9 % yield, with 1,8-cineole (44.34 %), camphor (16.74 %), α-pinene (10.07 %) and borneol (5.02 %) as the main components. Bioassay test revealed that R. Officinalis EO exhibited a larvicidal activity against fourth instar larvae at 24 hours (LC25, LC50 and LC90 values were 39.47, 51.33 and 86.77 ppm, respectively). When applied to its LC25 and LC50, EO induced a significant decrease of larvae morphometric parameters and disturbed energy reserves with a marked lipid decrease at different periods. Also, treatment-induced stimulation of the detoxification system is highlighted by GST activity increase and GSH level decrease.

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