Study looks at DEET and natural tick repellents

Ticks patiently hold on to blades of grass and shrubs in a position known as “questing” as they await their next meal or host. “Almost blind, ticks rely on chemosensation to identify and locate hosts for a successful blood meal,” write the authors of “Behavioral responses of Ixodes scapularis tick to natural products: development of novel repellents.”¹

 

As the number of tick-borne diseases grows and the geographical spread of ticks continues, there is increasing interest in what repellents are effective, safe and environmentally friendly. But little is known about how exactly ticks detect odors and what smells repel them.

“Improving our understanding of tick olfactory mechanisms and odor driven behaviors is key to enabling development of new repellents,” writes Faraone.

Given the health concerns over DEET, researchers are turning their attention to plant-based repellents. “Plant-derived essential oils are natural products that exhibit insecticidal and repellent activities and represent a promising alternative to synthetic repellants,” Faraone writes.

Lemongrass essential oil

“In behavioral bioassays we reported that lemongrass essential oil and its main chemical constituents (such as geraniol, β-citronellol and citral), as well as PEA [phenethyl alcohol], were significantly repellent to I. scapularis nymphs,” writes Faraone.

However, “the efficacy of lemongrass essential oil was dose-related, and was effective in repelling up to 76% of I. scapularis nymphs after 10 minutes when applied at the highest tested concentration.”

Study examines natural plant-based substances to repel ticks. Click To Tweet

The substance was more effective at higher concentrations in repelling ticks. But, the effect declined after 2 hours from the first application to 62.5% compared to a DEET-based product of 87.7%.

The authors did not report on the repellent effects outside the lab. And given that the formulation was proprietary, its ingredients were not disclosed.

However, they found that “PEA- and geraniol-based formulas exerted an effective repellent action representing a valid natural alternative to synthetic repellents already available on the market.”

DEET

DEET (diethyltoluamide) repels ticks but its use raises environmental and health concerns. The concentration of DEET also affects its ability to repel ticks, as shown below:

0% of DEET = 8.5% repelled
5% of DEET = 16.6% repelled
10% of DEET = 30.4% repelled
20% of DEET = 68.9% repelled
40% of DEET = 88% repelled

Interestingly, 0% DEET repelled 8.5% of ticks at 10 minutes. This is similar to the placebo effect.

The actual concentration of DEET from the manufacturer is 25% to 30%. The actual concentration on the skin for DEET or the proprietary products was not described in the study.

Most importantly, the study was completed on a paper filter. It remains to be seen how DEET or the natural-based products will work on people.

References:
  1. Faraone N, MacPherson S, Hillier NK. Behavioral responses of Ixodes scapularis tick to natural products: development of novel repellents. Exp Appl Acarol. 2019 Sep 28.
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