Chemical Composition and Insecticidal Activity of Ethanol Extracts of Clove Seed, Onion Peels and Bay Leaf on Adult Prostephanus truncatus of Stored Maize

Prostephanus truncatus poses a significant threat to global food security, particularly in stored maize and cassava, due to substantial postharvest losses. Botanical insecticides offer a sustainable and environmentally protective option for stored products. This study investigated the chemical composition and insecticidal efficacy of ethanolic extracts from clove seed (Syzygium aromaticum), onion peel (Allium cepa), and bay leaf (Laurus nobilis) against adult P. truncatus infesting stored maize. Ethanolic extracts were prepared from clove seed, onion peels, and bay leaves. Their chemical compositions were characterized using GC-MS. Insecticidal activity was evaluated by assessing adult mortality, seed damage, and F1 progeny emergence in P. truncatus exposed to varying concentrations (5%, 10%, 15%) of the extracts over 96 hours. A synthetic insecticide (DDVP) served as a standard control. All extracts demonstrated concentration and exposure time dependent insecticidal effect. Syzygium aromaticum and Allium cepa showed strong insecticidal effects, achieving 100% mortality at 15% concentration within 72 hours, comparable to the synthetic standard. GC-MS analysis revealed high concentrations of phenolic compounds (e.g., Phenol-2-methoxy-3-(propenyl), Phenol, 2-methoxy-4-(2-propenyl)-, acetate) and terpenes (Caryophyllene) in S. aromaticum and Catechol and Ethyl alpha-d-glucopyranoside as major constituents in Allium cepa. Laurus nobilis demonstrated lower, but notable, insecticidal activity, with Andrographolide and Eucalyptol as primary compounds. S. aromaticum significantly reduced seed damage and suppressed F1 progeny emergence, proving most effective in protecting stored maize. These findings revealed the potential of these plant-based alternatives for developing sustainable and environmentally friendly strategies to manage stored product pests, thereby reducing reliance on synthetic chemicals and enhancing food security.