Efficacy of Botanical Extract Formulations of Zanthroxylum usambarense and Warburgia ugandensis on Post-Harvest Management of Sitophilus zeamais in Maize

Sitophilus zeamais causes significant losses to maize produce worldwide. The use of biodegradable and environmentally friendly botanicals as an alternative to synthetic pesticides is increasingly becoming important. Therefore, we sought to determine the use of plant extract formulations to manage S. zeamais during storage. Crude Zanthroxylum usambarense and Warburgia ugandensis stembark extracts were used for contact toxicity and repellent bioassays against S. zeamais. The formulations that exhibited the highest repellence and mortality were tested for insecticidal activity during storage for six months. Phytochemical profiles of the extracts were determined using GC-MS, and molecular docking of active compounds against insect target proteins was done. Mortality analyses revealed LD50 values of 114.89 µg/mL and 197.19 µg/mL for Z. usambarense’s hexane and methanol organic extracts, respectively. Warburgia ugandensis extracts had LD50 values of 69.25 µg/mL and 163.52 µg/mL, respectively. Extract formulations achieved weevil perforation index values of <50.00 in all treatments. The docking analysis showed the pesticidal potential of several compounds, and mortality could be attributed to Eugenol (19.28%), 1,8-cineole (5.78%) and Linalool (21.42%). The tested botanicals have demonstrated their ability to suppress S. zeamais development in stored maize and could be utilized to protect maize grains during storage.