Biological activity of Trachystemon orientalis extracts against Sitophilus oryzae and Oryzaephilus surinamensis

Stored product pests, such as Sitophilus oryzae and Oryzaephilus surinamensis, pose significant threats to global grain storage. Plant extracts rich in phenolics offer environmentally friendly alternatives to synthetic pesticides for managing these pests. This study is the first to evaluate the biological activity of shade-dried (GS) and oven-dried (ES) water extracts of Trachystemon orientalis against S. oryzae and O. surinamensis. Phytochemical analysis revealed that the GS extract exhibited higher total phenolic content and antioxidant capacity compared to the ES extract. Specifically, the GS extract contained higher concentrations of abscisic acid (3346.76 mg/10⁶ g dried matter (dm)) and caffeic acid (1666.17 mg/10⁶ g dm), whereas the ES extract was richer in o- and p-salicylic acid, p-coumaric acid, and rosmarinic acid. Orientation assays conducted at four concentrations (62.5-500 ppm) revealed time- and concentration-dependent changes in the distribution of adults between treated and control compartments. After 120 h, the presence of O. surinamensis at the GS 500 ppm site decreased to 44% (G = 36, p ≤ 0.05), while S. oryzae presence dropped to 33% (G = 31.4, p ≤ 0.05). Furthermore, higher concentrations of the GS extract significantly reduced F1 adult emergence for both pests (p < 0.05, Two-Way ANOVA). These findings suggest that T. orientalis extracts, particularly GS, represent promising environmentally friendly alternatives to chemical pesticides for the management of stored product pests. The efficacy of these extracts is closely associated with their higher phenolic content and specific bioactive compounds.