Phytochemical characterization and pesticidal efficacy of garlic and chilli extracts and their chitosan-based formulations

This study characterized the phytochemical composition of Allium sativum (garlic) and Capsicum frutescens (chilli pepper) extracts and evaluated the pesticidal efficacy of their chitosan-based formulations against five agricultural pests. Aqueous extracts were analyzed by HPLC and FTIR and used in pesticidal bioassays, while methanolic and n-hexane extracts were analyzed by GC-MS. HPLC identified phenol as the dominant constituent across all preparations, with chlorogenic acid and ferulic acid characteristic of garlic, and coumaric acid and zeaxanthin characteristic of chilli. The chitosan-based formulations contained more phenol than the crude extracts, consistent with preferential retention of phenolic constituents within the chitosan matrix, a finding corroborated by UV-Vis spectroscopy through a bathochromic shift in both formulations, and by FTIR through the preservation of phenolic hydroxyl groups across all samples. GC-MS profiling identified fatty acids, fatty acid methyl esters, and terpenoids across the six sample preparations, with the combined chitosan-based formulations showing the broadest compound profile relative to single-component preparations. Pesticidal bioassays against Oecophylla smaragdina (weaver ant), Rhipicephalus microplus (tick), Acanthoscelides obtectus (bean weevil), Chrysocoris stollii (jewel bug), and Tribolium castaneum (red flour beetle) confirmed that chitosan-based formulations outperformed crude extracts across all species. The garlic and chilli chitosan-based formulations achieved 100% mortality against weaver ant and red flour beetle at 24 h, while the combined formulation outperformed individual preparations against bean weevil and achieved 100% mortality in red flour beetle more rapidly. These findings support garlic and chilli chitosan-based formulations as plant-derived alternatives to synthetic pesticides in agricultural pest management.