Potential use of Trachystemon officinalis (L.) G. Don (Boraginaceae) plant extracts in the control of Tetranychus urticae Koch (Acari: Tetranychidae) and the relationship between its biological activity and phenolic compounds

Abstract

This study investigated the acaricidal and repellent properties of Trachystemon orientalis (L.) G. Don (Boraginaceae) extracts against Tetranychus urticae Koch (Acari: Tetranychidae), a significant agricultural pest. Extracts were obtained from plant material subjected to shade and oven drying, using distilled water, methanol, and 75 % methanol containing 0.1 % formic acid. The aqueous extract prepared from oven-dried material (ES) exhibited the highest mortality, causing 92.93 % mortality at 10 % concentration after 24 h. In contrast, the methanol-formic acid extract from shade-dried material (GF) showed the strongest repellent activity (86.67 %) at 1 % concentration, with the effect persisting over 24 h. Biochemical profiling through LC-MS/MS identified major phenolic constituents, including rosmarinic acid, caffeic acid, o- and p-salicylic acid, p-coumaric acid, and protocatechuic acid. Rosmarinic acid was the most abundant phenolic compound, particularly in the GF. The extract also exhibited the strongest antioxidant activity (2073.42 mg GAE/100 g dry matter (dm)) in total phenolic content (TPC) and 2,2-diphenyl-1-picrylhydrazyl (DPPH) assays. A positive correlation was observed between the salicylic acid content of the ES extract and its acaricidal activity. High levels of rosmarinic acid, caffeic acid, p-salicylic acid, and chrysophanol were detected in shade-dried methanol (GM) and oven-dried methanol (EM) extracts, which had the highest repellency. Drying methods and solvents significantly influenced biological activity: water extracts were more acaricidal on T. urticae, while methanol extracts were more repellent. These findings suggest that T. orientalis could serve as a natural alternative to synthetic acaricides, offering a safer option for integrated pest management in sustainable agriculture. Future research should explore field applications, interactions with biopesticides, and effects on other pest populations and ecosystems.