Three molecules found in rosemary or nutmeg essential oils repel ticks (Dermacentor variabilis) more effectively than DEET in a no‐human assay

Abstract

BACKGROUND Development of new personal repellents to prevent tick bites is progressing to keep up with the increasing threat of tick‐borne diseases in humans. However, the market share of natural, plant‐based repellents is still quite small. We tested all of the major (>1%) components found in the essential oils of rosemary (Spanish variety) and nutmeg. These were tested with Dermacentor variabilis ticks, a robust tick capable of vectoring human diseases, in a no‐human horizontal Petri dish assay. For comparison, we also tested the active ingredients currently recommended by the CDC and EPA as personal repellents for use against ticks. RESULTS Of the 16 oil components tested, three performed significantly better than N,N‐diethyl‐meta‐toluamide (DEET) in our assay. These compounds were myristicin and safrole found in the nutmeg oil, and terpinolene found in nutmeg oil and as a minor (<1%) constituent of rosemary oil. The current market natural product, 2‐undecanone, also performed strongly in our assay. CONCLUSIONS Our assay focused on comparing active ingredients as potential repellents and found that many natural products can elicit a strong response from ticks. Terpinolene is the most promising active ingredient identified, owing to human health concerns regarding myristicin and safrole. Our results from examining individual terpenoids from two essential oils suggest that there remain unexploited natural compounds that could be further developed for new personal tick repellents. © 2020 Society of Chemical Industry

Persistence Enhancement of a Promising Tick Repellent, Benzyl Isothiocyanate, by Yeast Microcarriers

“…IR3535, which was used as a positive control in this study, showed repellency against H. longicornis nymphs at dosages up to 0.05 mg/cm 2 . Similar results were obtained by Wong et al [21], who observed that synthetic IR3535 showed lower repellent activity against American dog ticks (Dermacentor variabilis) than did the active ingredients (myristicin, safrole, and terpinolene) in rosemary and nutmeg essential oils. Commercially available synthetic repellents may not be satisfactorily effective against ticks because many of them have been developed to protect humans from mosquitos [22,23].…”

“…The repellent effects of A. rusticana root oil and the isolated compound and its derivatives against H. longicornis nymphs were tested using a filter paper bioassay as described by Del Fabbro and Nazzi [35] and Wong et al [21] with slight modifications. Two concentric circles were drawn on the test filter paper, one with a radius of 1.5 cm (start line) and the other with a radius of 3.5 cm (finish line).…”

Back to the Roots—An Overview of the Chemical Composition and Bioactivity of Selected Root-Essential Oils

“…Among 16 tested main constituents from rosemary and nutmeg EOs, safrole exerted potential repellent activity—similar to myristicin, and terpinolene— Dermacentor variabilis ticks, known as a robust tick capable of vectoring human diseases. The median repellent times caused over a 300 s observation period in a non-human subject screening assay was higher than synthetic diethyltoluamid (DEET) and the parent EOs [ 256 ].…”

Evaluation of a quasi‐dimeric eugenol derivative as repellent against the stored grain insect pest Sitophilusoryzae (Coleoptera Curculionidae)

“…This finding is consistent with other studies that found that EOs and their compounds may show repellent efficacy equal to or greater than commonly used synthetic repellents. [21][22][23]…”