Contact and fumigant toxicities of 3-methylphenol isolated from ostericum koreanum and its derivatives against house dust mites

The acaricidal activities of an active constituent derived from Ostericum koreanum roots and its derivatives were determined using fumigant and direct-contact toxicity bioassays against Dermatophagoides farinae and Dermatophagoides pteronyssinus. This was compared with that of a commercial acaricide (benzyl benzoate). In the fumigant toxicity bioassay, 4-chloro-6-isopropyl-3-methylphenol (0.29 μg/cm²) was 37.17 times more effective than benzyl benzoate (10.78 μg/cm²) against D. farinae, followed by 6-fluoro-3-methylphenol (0.57 μg/cm²), 3-methylphenol (0.63 μg/cm²), 4-chloro-3-methylphenol (0.75 μg/cm²), and 4-isopropyl-3-methylphenol (0.78 μg/cm ²). In the direct-contact toxicity bioassay, 4-chloro-6-isopropyl-3- methylphenol (0.21 μg/cm²) was 36.81 times more toxic than benzyl benzoate (7.73 μg/cm²) against D. farinae, followed by 6-fluoro-3-methylphenol (0.40 μg/cm²), 3-methylphenol (0.41 μg/cm²), 4-isopropyl-3-methylphenol (0.56 μg/cm²), and 4-chloro-3-methylphenol (0.60 μg/cm²). The acaricidal effects of 3-methyphenol derivatives against D. pteronyssinus were similar to those against D. farinae. In structure-activity relationships, acaricidal activities could be related to the introduction of chloro, fluoro, and isopropyl functional groups onto the 3-methylphenol skeleton. These results indicate that naturally occurring 3-methylphenol and its derivatives are potential house dust mite control agents.