Acaricidal activity and function of mite indicator using plumbagin and its derivatives isolated from Diospyros kaki Thunb. roots (Ebenaceae).

Acaricidal effects of materials derived from Diospyros kaki roots against Dermatophagoides farinae and D. pteronyssinus were assessed using impregnated fabric disk bioassay and compared with that of the commercial benzyl benzoate. The observed responses varied according to dosage and mite species. The LD50 values of the chloroform extract of Diospyros kaki roots were 1.66 and 0.96 microg/cm2 against D. farinae and D. pteronyssinus. The chloroform extract of Diospyros kaki roots was approximately 15.2 more toxic than benzyl benzoate against D. farinae, and 7.6 times more toxic against D. pteronyssinus. Purification of the biologically active constituent from D. kaki roots was done by using silica gel chromatography and high-performance liquid chromatography. The structure of the acaricidal component was analyzed by GCMS, 1H-NMR, 13C-NMR, 1H-13C COSY-NMR, and DEPTNMR spectra, and identified as plumbagin. The acaricidal activity of plumbagin and its derivatives (naphthazarin, dichlon, 2,3-dibromo-1,4-naphthoquinone, and 2-bromo-1,4- naphthoquinone) was examined. On the basis of LD50 values, the most toxic compound against D. farinae was naphthazarin (0.011 microg/cm2) followed by plumbagin (0.019 microg/cm2), 2- bromo-1,4-naphthoquinone (0.079 microg/cm2), dichlon (0.422 microg/ cm2), and benzyl benzoate (9.14 microg/cm2). Additionally, the skin color of the dust mites was changed from colorless-transparent to dark brown-black by the treatment of plumbagin. Similar results have been exhibited in its derivatives (naphthazarin, dichlon, and 2-bromo-1,4-naphthoquinone). In contrast, little or no discoloration was observed for benzyl benzoate. From this point of view, plumbagin and its derivatives can be very useful for the potential control agents, lead compounds, and indicator of house dust mites.