Phenylpropanoid esters, particularly methyl cinnamate and ethyl 4-methoxycinnamate, drive the insecticidal potential of Alpinia galanga root oils against stored-product insects

Botanical options that act effectively in the vapor phase are sought for postharvest protection with minimal residues. We compared an ester-enriched steam distillation–extraction (SDE) oil and a hexane extract (HE) from Alpinia galanga roots, profiled their chemistry by GC–MS, and quantified fumigant and contact toxicities against four major stored-product pests under standardized bioassays. Across species, SDE consistently outperformed HE as a fumigant: LD₅₀ (μg/cm³) for SDE were 38.56 for Plodia interpunctella larvae, 33.64 for Sitotroga cerealella adults, 18.27 for Sitophilus oryzae adults, and 21.47 for S. zeamais adults, with steeper slopes and good model fits; corresponding HE LD₅₀ values were higher (64.16, 52.31, 34.26, and 42.96 μg/cm³). In contact bioassays the same rank order held, with SDE LD₅₀ (μg/cm²) of 43.46 (P. interpunctella larvae), 39.57 (S. cerealella adults), 25.02 (S. oryzae), and 30.63 (S. zeamais). The superior activity of SDE aligns with its composition—methyl cinnamate (43.32 %) and ethyl 4-methoxycinnamate (31.36 %) are enriched relative to HE—implicating volatility-driven exposure and facilitated cuticular penetration as determinants of efficacy. Whole-oil versus single-constituent contrasts further indicate matrix effects that can amplify coleopteran control, whereas isolated esters show more variable performance across taxa. Taken together, the results position ester-rich A. galanga SDE oil as a promising vapor-phase botanical for integration into closed/hermetic postharvest systems, with future work geared to mechanistic validation (AChE kinetics, synergist diagnostics, and cuticle-flux bioassays) and formulation for grain-quality stewardship.