Protective Effects of Tephrosia vogelii Leaf Extracts against Sitophilus zeamais and Acanthoscelides obtectus in the Storage of Maize and Beans

This study evaluated the protective effect of Tephrosia vogelii leaf extracts against Sitophilus zeamais and Acanthoscelides obtectus in the postharvest storage of maize and beans. The study was motivated by increasing food-security concerns, as global postharvest food losses are estimated at 13.3%, with sub-Saharan Africa recording about 23.0% and cereals and pulses accounting for approximately 8.4% of global production losses. Dried T. vogelii leaves were extracted with ethanol and n-hexane using a Soxhlet extractor, and extract concentrations of 5%, 10%, 15%, and 20% were prepared. Phytochemical screening and GC-MS analysis were used to characterize the extracts. Repellency, mortality, antifeedant, weight-loss, and shelf-life bioassays were conducted under laboratory conditions to ascertain the potency of the phytochemicals against the insects. Qualitative screening revealed that the ethanol extract contained flavonoids, saponins, phenols, tannins, steroids, terpenoids, alkaloids, and cardiac glycosides, while the hexane extract contained flavonoids, steroids, terpenoids, and cardiac glycosides. GC-MS analysis showed important bioactive compounds, including rotenone, rutin, elliptone, deguelin, and tephrosin in the ethanol extract, and naphthalene, deguelin, germacrene D, pentadecane, neophytadiene, and rotenone in the hexane extract. The extracts produced significant mortality, repellency, and antifeedant effects against both insects (p < 0.05), with effects generally increasing with concentration and exposure time. At 20%, ethanol extract recorded a low grain loss of 11.53% for S. zeamais and 18.60% for A. obtectus, while hexane extract recorded 17.39% and 17.91%, respectively, but the untreated control recorded more than 70% loss. The study concludes that T. vogelii, especially the ethanol extract, has promising botanical insecticidal, repellent, and antifeedant potential for protection of stored maize and beans.