Phytochemical profling, spectroscopic characterization, and acaricidal activity of Tephrosia vogelii leaf extract from Laikipia county, Kenya

Abstract

This study aimed to profle the phytochemical profling constituents, characterize the functional groups spectroscopically, and evaluate the acaricidal activity of Tephrosia vogelii leaf extract from Laikipia County, Kenya. Ultrasound assisted sequential extraction using n-hexane, chloroform, and ethanol was employed to obtain crude leaf extracts, followed by qualitative phytochemical screening, FTIR and GC–MS analysis, and AAS based heavy metal quantifcation. The ethanol extract was further tested for acaricidal activity against Rhipicephalus sanguineus using adult and larval immersion tests. Results revealed a rich spectrum of bioactive compounds, including favonoids and rotenoids, saponins, alkaloids, terpenoids, phenols, and glycosides, with deguelin and tephrosin identifed as key acaricidal agents. FTIR and GC–MS showed characteristic peaks at 3446.79 cm⁻ 1 (O–H/N–H), 1743.65 cm⁻ 1 (C=O lactone), and 1535.34 cm⁻ 1 (aromatic C=C), consistent with rotenoid and favonoid structures. AAS detected elevated levels of heavy metals such as Fe, Mn, and Hg, exceeding WHO limits. Biologically, the ethanol extract produced up to 99.74% larval mortality at 40–50 mg/mL (LC₅₀=8.58 mg/mL) and strongly inhibited egg laying (20.03% at 40 mg/mL). The study concludes that Tephrosia vogelii from Laikipia is a promising natural source of bioactive phytochemicals with potent acaricidal activity against Rhipicephalus sanguineus (R. sanguineus). It is recommended that future work focus on purifcation and fractionation of the ethanol extract to isolate key rotenoids and favonoids and develop standardized, environmentally safe formulations for tick control in livestock and integrated pest-management programs.