Acaricidal potency of active constituent isolated from Mentha piperita and its structural analogs against pyroglyphid mites

This study was conducted to evaluate acaricidal toxicities of an active compound isolated from Mentha piperita leaves and its structural analogs against pyroglyphid mites, Dermatophagoides farinae, and D. pteronyssinus. Menthol was isolated through chromatographic techniques. Based on the LD₅₀ values of M. piperita oil and menthol analogs against D. farinae and D. pteronyssinus, obtained using the impregnated cotton fabric disk method, the acaricidal activities of (−)-menthol (0.19 and 0.12 μg/cm³) were 194 and 164 times higher than those of DEET (36.89 and 19.72 μg/cm³), followed by that of (±)-menthol (0.23 and 0.21 μg/cm³), (+)-menthol (0.29 and 0.23 μg/cm³), (+)-neomenthol (0.32 and 0.26 μg/cm³), (+)-isomenthol (0.34 and 0.29 μg/cm³), M. piperita oil (1.50 and 1.00 μg/cm³), 4-methylcyclohexanol (5.45 and 4.76 μg/cm³), 2-methylcyclohexanol (7.64 and 5.67 μg/cm³), and 1-methylcyclohexanol (9.82 and 8.56 μg/cm³). Similarly, the acaricidal activities of M. piperita oil and menthol analogs in the filter paper method were similar to those in the impregnated cotton fabric disk method against Dermatophagoides spp. In the structure–activity relationships, the isopropyl (C₃H₇) functional group on the cyclohexane skeleton influenced acaricidal activity the most, followed by the hydroxyl (OH) and methyl (CH₃) functional groups. This study indicates that M. piperita oil and menthol analogs have the potential for development as preventive agents for control of Dermatophagoides spp.