Chemical characterisation and in vitro larvicidal activities on Anophele larvae of the essential oils of Cymbopogon schoenanthus L. spreng (Poaceae) and Endostemon tereticaulis poir (Lamiaceae)

Abstract

In Niger, traditional medicine represents an important cultural and economic heritage. The use of plants in the fight against malaria mosquitoes has been the subject of several ethnobotanical surveys which led to the identification of several plants including Cymbopogon schoenanthus L. spreng and Endostemon tereticaulis Poir. The aim of this study is to assess the larvicidal properties of the essential oils of these two species. The essential oil of each plant was extracted by hydrodistillation, these oils were analysed by gas chromatography/mass spectrometry (GC/MS). Larvicidal tests were carried out according to a WHO protocol. Essential oil yields were 0.7% and 0.5% respectively for C. schoenanthus and E. tereticaulis. The analysis of the two essential oils showed that they are monoterpene in nature, with the main constituents piperitone (63.61%), 2-carene (20.84%) and limonene (4.94%) for C. schoenanthus, and carvacrol (79.40%), thymol (6.49%) and ?-terpinene (2.60%) for E. tereticaulis. The results of the in vitro larvicidal tests showed strong larvicidal activity against Anopheles larvae after 24 and 48 hours of exposure. The lethal doses which cause 100% mortality are 125mg/L for C. schoenanthus essential oil and 150 mg/L for E. tereticaulis essential oil. The essential oil of C. schoenanthus was more active than that of E. tereticaulis, although these two essential oils were less active than the reference product, deltamethrin. These results justify the use of these two plants in Niger to combat malaria mosquitoes.