In vitro repellent efficacy of Pogostemon cablin (Blanco) Benth. [Lamiaceae] essential oil and its nanoemulsion against Haemaphysalis longicornis (Acari: Ixodidae)

This study was conducted to assess the repellent activity of Pogostemon cablin (Blanco) Benth. [Lamiaceae] essential oil (EO) and its nanoemulsion (NE) against Haemaphysalis longicornis nymphs. Pogostemon cablin EO nanoemulsion (PCNE) was prepared by ultrasonic emulsification using P. cablin EO and a surfactant, Tween 80. The results of gas chromatography–mass spectrometry analysis showed that the major component of P. cablin EO was patchouli alcohol (32.04%), followed by δ-guaiene (18.13%), α-guaiene (16.76%), seychellene (7.49%), and β-patchoulene (5.09%). The droplet sizes of PCNEs formulated using P. cablin EO and Tween 80 in ratios of 1:1, 1:2, and 1:3 were 23.8, 20.1 and 17.7 nm, respectively, indicating that the increase in the ratio of Tween 80 led to a decrease in droplet size. All essential oil preparations had an acceptable polydispersity index of 0.5 or less. The P. cablin EO and Tween 80 ratio of 1:3 was selected as the optimal formulation with the smallest droplet size; transmission electron microscopy indicated the formation of uniform spherical droplets. PCNE (84.0%) showed a higher repellent activity against H. longicornis nymphs than P. cablin EO (72.0%). The nanoemulsion is suitable for improving the repellent activity of P. cablin EO and is a potential repellent for H. longicornis.