Evaluation of DEET and eight essential oils for repellency against nymphs of the lone star tick, Amblyomma americanum (Acari: Ixodidae)

Authors: MENG, HAO - Hebei University; Li, Andrew; COSTA JUNIOR, LIVIO - Federal University - Brazil; CASTRO-ARELLANO, IVAN - Texas State University; LIU, JINGZE - Hebei University

Submitted to: Experimental and Applied Acarology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/5/2015
Publication Date: 12/26/2015
Citation: Meng, H., Li, A.Y., Costa Junior, L.M., Castro-Arellano, I., Liu, J. 2015. Evaluation of DEET and eight essential oils for repellency against nymphs of the lone star tick, Amblyomma americanum (Acari: Ixodidae). Experimental and Applied Acarology. 68(2):241-249.

Interpretive Summary: Ticks are vectors of pathogens that cause diseases affecting humans, livestock, and wildlife. Major tick-borne diseases (TBDs) in the United States include anaplasmosis, babesiosis, ehrlichiosis, Lyme disease (LD), Rocky Mountain spotted fever, and tularemia. Lyme disease alone is the 5th most common illness reported to the Centers for Disease Control Prevention. TBDs are transmitted from animals to humans via tick bite. The use of permethrin-treated protective clothing and other repellents may help prevent tick bite, and reduce the risk of Lyme disease and other tick-borne human illness. DEET is the common chemical compound found in most commercially available insect/tick repellent formulations. Due to problems associated with use of DEET and its potential risk to human health, safer and more effective alternatives are being investigated by scientific community. We conducted a study to evaluate repellency of eight essential oils against the lone star tick, Amblyomma americanum, one of most widely distributed tick species and disease vectors in the U.S. Tick repellency was determined for each essential oil using a vertical filter paper bioassay technique. The effectiveness of these essential oils was compared with that of DEET against lone star tick nymphs. These natural essential oils demonstrated various repellencies against nymphs of the lone star tick, but none was as effective as DEET. The results are of interest to researchers, public health professionals, pest managers concerned with medical and veterinary risks associated with ticks, and companies marketing commercial tick repellents. Future studies will focus on testing mixtures of essential oils, which could lead to discovery of combined tick repellent formulations for commercial development.

Technical Abstract: Eight commercially available essential oils (oregano, clove, thyme, vetiver, sandalwood, cinnamon, cedarwood, and peppermint) were evaluated for repellency against host-seeking nymphs of the lone star tick, Amblyomma americanum. Concentration- repellency response was established using the vertical paper bioassay technique for each essential oil and compared with that of N,N-diethyl-3-methyl benzamide (DEET), a standard repellent compound present in many commercial repellent formulations. The effective concentration of DEET that repels 50% of ticks (EC50) was estimated at 0.02 mg/cm2, while EC50s of the essential oils fall between 0.113 and 0.297 mg/cm2. Based on EC50 estimates, oregano essential oil was the most effective among all essential oils tested, followed by clove, thyme, vetiver, sandalwood, cinnamon, cedarwood, and peppermint oils. None of those essential oils demonstrated a level of tick repellency that is close to that of DEET. Results from this study illustrated the challenge in search for more effective natural tick repellents.