Phytochemical constituents and larvicidal efficacy of leaf extracts of Aristolochia elegans (Aristolochiaceae)

Abstract

The crude extracts of leaves of Aristolochia elegans Mast (Aristolochiaceae) collected from Rombo district in Kilimanjaro, Tanzania (3˚11ʹ15.4ʹʹS 37˚37ʹ05.5ʹʹE), were obtained by maceration of sample at room temperature followed by phytochemical analysis by GC-MS. The GC-MS analysis of the extracts showed that the main content was Caryophyllene among all extract investigated, followed by Calarene and Bicyclogermacrene. The crude extracts were then evaluated for larvicidal activity using World Health Organization (WHO) procedures against the third Instar larvae of Anopheles gambiae and monitored at an interval of 24 h, from 24 to 72 h and activity was recorded for various concentrations of the ranging from 25 to 200.0 μg/mL. Mortality effect of investigated extracts against laboratory-reared larvae had variations indicated by their LC50. LC50 for ethanol leaf extract were 165 µg/mL and 135 µg/mL after 48 and 72 h, respectively. LC50 for dichloromethane leaf extract were 145 µg/mL and 136 µg/mL after 48 and 72 h, respectively. For n-hexane extract, LC50 were 34 µg/mL and 33 µg/mL after 48 and 72 h, respectively. The remarkable differences in the larvicidal activity of crude extracts against the larvae of A. gambiae were due to qualitative and quantitative variations of the components, exemplified by the presence of sesquiterpenes with caryophyllene skeleton. The findings indicate that n-hexane leaf extract has potentials for use in the control of A. gambiae larvae and may be useful in the search for novel and effective natural compounds as larvicides.