Laboratory evaluation of methanol extracts from three plant species as repellents against a vector of scrub typhus, Leptotrombidium pallidum (Acari: Trombiculidae)

The objective of this study was to assess data for effective control of Leptotrombidium pallidum. Insecticidal and repellent activities of ten acaricides and three plant methanol extracts were evaluated to the mite species with impregnated fabric disk and ring fabric diffusion assays, respectively. In impregnated fabric disk assay for acaricidal susceptibility of L. pallidum to test materials, based on 24-h LC50 values, the highest susceptibility was observed in deltamethrin with an LC50 value of 0.003 mg/cm2, followed by Cinnamomum cassia methanol extract with an LC50 value of 0.008 mg/cm2. The lowest toxicity to cyfluthrin was observed with an LC50 value of 0.064 mg/cm2. Leptotrombidium pallidum showed higher acaricide susceptibility to methanol extracts of Illicium verum and C. cassia than five synthetic acaricides. In repellent test by ring fabric diffusion assay, based on 5-min RC50 values, C. cassia oil exhibited the strongest repellent activity with an RC50 value of 1.52 mg/cm2, followed by methanol extracts of I. verum and DEET with RC50 values of 2.85 and 3.85 mg/cm2, respectively. In repellency after exposure, based on RT50 values, permethrin demonstrated the longest repellent activity with an RT50 value of 434.9 min, followed by penitrothion and DEET with RT50 values of 358.7 and 323.2 min, respectively. Methanol extracts of I. verum and C. cassia showed RT50 values of 120.6 and 152.7 min, respectively. The results demonstrated the potential for L. pallidum control using some plant oils and the study offers basic control information related to the chigger mite species in field.