Bioassay-guided Studies on Pelargonium graveolens Essential Oil against Lone Star Ticks
Tick-borne diseases, such as Lyme disease and Rocky Mountain spotted fever still constitute a serious problem for thousands of Americans. The principal vectors are three-host ticks that use a variety of vertebrate hosts associated with forested habitats. Synthetic repellents, in particular DEET (N,N-diethyl-3-methyl benzamide)-based products still represent the major chemical defense against ticks , but there are concerns about the safety of these products. DEET has been associated with seizures and encephalopathy in children, and parents and caregivers are nervous about the effect of repellents on their children's sensitive skin. For these reasons, new and safer alternatives are needed. Natural products, and essential oil in particular, are usually regarded as a safer and “greener” alternative to synthetic compounds and many natural compounds are known for their repellency properties. Nonetheless, essential oils still constitute an unexplored source of tick repellents. Geranium (Pelargonium graveolens) essential oil is widely known for its anti-mosquito activity. Although insecticidal and repellent activities of geranium oil have been previously reported , no reports about the active compounds from geranium essential oil as active tick repellents have been published.
In the current investigation, bio-guided fractionation of geranium essential oil has been performed. Several active constituents have been identified. In particular, the authors report here for the first time the biological activity of (-)-10-epi-γ-eudesmol (1) as active tick repellent.
Acknowledgements: This study was supported in part the USDA, ARS grant No. 56 – 6402 – 1-612 and Deployed War-Fighter Protection Research Program Grant funded by the U.S. Department of Defense through the Armed Forces Pest Management Board. The authors thank Agilent Technologies, Inc. (Santa Clara CA, USA) for provision of the analytical instrumentation used in this study. References:  Debboun M, Frances et al. (2007) “Insect Repellents: Principles, Methods and Uses”, CRC Press LLC  Jaenson TGT, Garboui S, Palsson K (2006)J Med Entomol, 43: 731 – 736.