Comparative Insecticidal Activity and Acetylcholinesterase Inhibition of Vitex doniana Stem Extract and Azadirachta indica Seed Oil against Sitophilus zeamais.

Sitophilus zeamais is among the most destructive pests of stored maize, causing post-harvest losses in quantity and quality. Although synthetic insecticides are widely used for its control, concerns regarding insecticide resistance, pesticide residues and environmental and human health risks have increased interest in botanical alternatives. This study compared the insecticidal activity of Vitex doniana stem extract and Azadirachta indica seed oil against S. zeamais and assessed acetylcholinesterase (AChE) activity to provide insight into their mode of insecticidal action. Adult mortality, repellency, progeny emergence, emergence inhibition and lethal concentrations (LC50 and LC90) were evaluated at concentrations ranging from 0.3 to 24%. Both botanicals exhibited significant (p < 0.05) concentration-dependent insecticidal activity, with A. indica seed oil showing greater efficacy than V. doniana stem extract, achieving 93.33% and 71.67% mortality, respectively, at 24% concentration. Probit analysis yielded LC50 values of 1.23% for A. indica seed oil and 5.33% for V. doniana stem extract. Repellency at 24% was 86.67% for A. indica seed oil and 60.00% for V. doniana stem extract. Both treatments suppressed progeny emergence, with A. indica seed oil achieving 99.75% emergence inhibition compared with 71.76% for V. doniana stem extract at 24%. Both treatments reduced AChE activity, with the lowest activity (0.0038 μmol/min) recorded in insects treated with 24% A. indica seed oil, suggesting that cholinergic interference may contribute to insecticidal activity. These findings suggest that both botanicals possess insecticidal activity against S. zeamais, with A. indica seed oil exhibiting greater efficacy and potential as a protectant for stored maize.