Phytochemical composition and repellency activity of Tephrosia vogelii leaf extracts against Aphis fabae Scopoli (Hemiptera: Aphididae)

Abstract

Global efforts to control crop pests have traditionally depended on inorganic insecticides, which unfortunately had harmful effects on the ecosystem hence sustainability and the importance of maintaining ecological balance such use of plant extracts has gained momentum. This study aimed to determine the chemical makeup and repellency activity of Tephrosia vogelii leaf extracts prepared using methanol and dichloromethane solvents. In addition, a one-way experiment in a completely randomized design with 3 replications was used to evaluate the repellency activity of Tephrosia vogelii leaf extracts against Aphis fabae at different concentrations and conducted at 1 hrs intervals for 5 hrs.  Phytochemical screening assays of Tephrosia vogelii leaf extracts indicated the presence of secondary metabolites such as flavonoids, anthraquinone, tannins, saponins, alkaloids and terpenoids. The LC-MS analysis identified 12 compounds. There is no clear evidence on the report of compounds such as 4,7-Dimethoxyisoflavone, Puerarin, 6,4-Dimethoxy-7-hydroxyiflavone, 3-hydroxy-7,8,4-trimethoxyflavone, curcumol, and Glycetein in Tephrosia vogelii. For all extracts of Tephrosia vogelii leaf, treatments revealed a significant repellency activity against black bean aphids ranging from 38.33% to 75 % after 5 hrs of exposure time. The comparison of the repellent effects of dichloromethane and methanol leaf extracts of Tephrosia vogelii indicated that dichloromethane leaf extract at 8g/ml exhibited the highest repellent activity (65.33%) than methanol leaf extract (61.67%) at similar concentration. Its effectiveness is potentially attributed to the presence of bioactive compounds such as deguelin, rotenone, and quercetin. However, a detailed lab and field research using pure compounds is suggested.