Synthetic insecticides such as organochlorines, carbamates, organophosphates or pyrethroids, used in the preventive fight against malaria, can be the cause of numerous cases of resistance in mosquitoes. Thus, the use of natural molecules with biodegradable insecticide or insect repellent properties and therefore more respectful of the environment and the ecosystem, could be an alternative to the use of synthetic insecticides. Within this framework, the present study concerns the evaluation of the larvicidal activity of essential oils of six (6) aromatic plants of Niger on the larvae of Anopheles gambiae s l.. The essential oil was analyzed by gas chromatography coupled to mass spectrometry (GC-MS) and the larvicidal tests were carried out according to a WHO protocol (1985). The analysis by gas chromatography (GC) and GC-MS showed that the essential oil of Ocimum americanum L. (dry leafy stems) is mainly composed of camphor (28.1%) and eucalyptol (17.6%). That of Cymbopogon citratus (dry leaves) is mainly composed of ?-citral (44.8%) and ?-citral (32.7%). D-limonene (96.1%) is the major constituent of the essential oil of Citrus sinensis (dry fruit pericarp). The essential oil of Ocimum basilicum (dry leafy stems), on the other hand, contains mainly ?-linalool (53.18%) and eucalyptol (10.28%). It was revealed in the essential oil of C. podocarpa (dry leaves) caryophyllene oxide (51.33%) and 2,5,9-trimethylcycloundeca-4,8-dienone (19.56%) as majority compounds. Bioassays showed that the essential oil of C. podocarpa (LD50 = 54.374 ppm) is the most active against Anopheles gambiae larvae followed by the sample of O canum (LD50 = 61.50 ppm). Medium activity was observed with the samples of C. giganteus (LD50 = 70.13 ppm), C. sinensis (LD50 = 105.13 ppm), C. citratus (LD50 = 114.36 ppm) and O. basilicum (LD50 = 135.45ppm). The essential oil samples in the present study are less active than deltamethrin (LD50 = 2.3 ppm). Despite this difference in activity essential oils could be of great interest in the formulation of new insecticides. These results could justify the traditional use of aromatic plants as repellents in Niger.

Keywords: Essential oils, Anopheles gambiae, larvicidal activity, malaria, Niger.