Extraction of ginkgolic acids from Ginkgo biloba L. exocarp and their efficacies against Tetranychus cinnabarinus

Spider mites cause substantial economic losses and are difficult to control in agricultural systems. Ginkgo biloba L. extract has potential as an acaricide, although its specific acaricidal components have yet to be identified. We used bioassay-guided isolation to isolate and purify three main ginkgolic acid (GA) compounds (C13:0, C15:1, and C17:1). Their chemical structures were identified as ¹H, ¹³C, and IR, respectively. The LC₅₀ values of GA C13:0, GA C15:1, and GA C17:1 against Tetranychus cinnabarinus were 777.75, 481.07, and 180.25 μg mL⁻¹, respectively, demonstrating high toxicity. The efficacies of 23% GA soluble liquid (SL) with a dosage of 1500 a.i. g·hm⁻² after 14 days were 82.45% and 85.41%, respectively, in Dali County and Chengcheng County, Weinan, China. The GA extraction process was optimized using methanol as the extraction solvent, heating and refluxing at 60 °C for 4 h at a solid-liquid ratio of 1:4, and repeating the process twice. The GA extraction rate of G. biloba exocarp was 43.2%, and the total extraction content of the three main GA compounds was 68.73%. Our optimization of the GA extraction process from G. biloba exocarp has the potential to be applied on an industrial scale, and GAs could be used as a commercial acaricide for controlling mites in the future.