jf400246a_si_001.pdf (1014.18 kB)
Bioactivity-Guided Investigation of Geranium Essential Oils as Natural Tick Repellents
journal contribution
posted on 2013-05-01, 00:00 authored by Nurhayat Tabanca, Mei Wang, Cristina Avonto, Amar G. Chittiboyina, Jon F. Parcher, John F. Carroll, Matthew Kramer, Ikhlas A. KhanThe evaluation of 10 essential oils
of geranium, Pelargonium graveolens (Geraniaceae), were all shown
to have repellent activity against nymphs of the medically important
lone star tick, Amblyomma americanum (L.). The biological tests were carried out using a vertical filter
paper bioassay, where ticks must cross an area of the paper treated
with repellent to approach host stimuli. One of the essential oil
samples that repelled >90% of the ticks at 0.103 mg/cm2 was selected for further fractionation studies. The sesquiterpene
alcohol, (−)-10-epi-γ-eudesmol, was isolated and identified
by spectral methods. (−)-10-epi-γ-Eudesmol at 0.103 and
0.052 mg of compound/cm2 of filter paper repelled 90 and
73.3% of the ticks, respectively. (−)-10-epi-γ-Eudesmol
exhibited similar repellency to the reference standard N,N-diethyl-meta-toluamide (DEET) at concentrations
of ≥0.052 mg of compound/cm2 of filter paper, with
(−)-10-epi-γ-eudesmol losing much of its repellency at
0.026 mg of compound/cm2 and DEET at 0.013 mg of compound/cm2. Isomenthone and linalool did not repel ticks at the concentrations
tested. Most repellents are marketed with much higher concentrations
of active ingredient than the concentrations of the natural repellents
tested herein; therefore, effective compounds, such as (−)-10-epi-γ-eudesmol,
found in geranium oil, have the potential for commercial development.