Efficacy of Some Indigenous Vegetable Oils in the Management of the Stored Maize Weevil, Sitophilus Zeamais (L.)

Postharvest infestation of maize by the maize weevil, Sitophilus zeamais, reduces grain quantity, market value and food and seed quality, while the limitations associated with synthetic insecticides create a need for effective, locally adaptable and low-risk alternatives. Laboratory study was conducted to evaluated indigenous vegetable oils as biorational strategy for managing S. zeamais in stored maize. The experiment assessed neem seed oil (NSO), sunflower oil (SFO) and olive oil (OO) at 2.5, 5, 7.5 and 10 ml. Egg oviposition, adult mortality grain damage, grain weight loss and progeny emergence were assessed. The results showed that neem seed oil, sunflower oil and olive oil can suppress S. zeamais and preserve maize grain when applied at adequate rates. Neem seed oil produced the fastest mortality response, with 10 ml causing complete adult mortality. Grain damage was completely prevented by NSO and OO at 7.5 and 10 ml, while progeny emergence was fully suppressed by NSO at 7.5 and 10 ml and by SFO and OO at 10 ml. The higher-rate oil treatments also maintained high grain mass and very low weight loss. These findings established a clear concentration effect; the oils were protective at all tested rates relative to the untreated infested control. NSO was the strongest oil for rapid adult control, whereas high rates of NSO and OO provided the most comprehensive grain protection. For maximum protection of maize grains against S. zeamais, neem seed oil and olive oil at 7.5-10 ml should be prioritized for sustainable grain protection.