Exploiting a natural instance of vertebrate-posed chemical aposematism for tick bite prevention: Repellency of Ixodes scapularis with (E)-Oct-2-enal

Authors: SIEGEL, ERIC - University Of Massachusetts, Amherst; GOODNOW, SOPHIA - University Of Massachusetts, Amherst; THOMPSON, LUCY - University Of Massachusetts, Amherst; NICOLSON, SARAH - University Of Massachusetts, Amherst; MACLEOD, ELIZABETH - University Of Massachusetts, Amherst; Li, Andrew; XU, GUANG - University Of Massachusetts, Amherst; RICH, STEPHEN - University Of Massachusetts, Amherst

Submitted to: PLOS ONE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/7/2025
Publication Date: 3/26/2025
Citation: Siegel, E.L., Goodnow, S., Thompson, L., Nicolson, S., Macleod, E., Li, A.Y., Xu, G., Rich, S.M. 2025. Exploiting a natural instance of vertebrate-posed chemical aposematism for tick bite prevention: Repellency of Ixodes scapularis with (E)-Oct-2-enal. PLOS ONE. 20(3). Article e0317975. https://doi.org/10.1371/journal.pone.0317975.
DOI: https://doi.org/10.1371/journal.pone.0317975

Interpretive Summary: Ticks are important vectors of some serious human and animal diseases, such as Lyme disease, anaplasmosis and babesiosis. Conventional tick control relies on chemical acaricides, including organophosphates and pyrethroids, the effectiveness and applicability of which are subject to factors such as variable susceptibility of those tick species, patterns of resistance, regional regulations, proper application technique, and adherence to recommended withdrawal periods for animal products. Repellent products are almost exclusively used to prevent bites of humans with sparing applications to clothing or skin. Few repellent products are used to protect livestock and wildlife. Continued research efforts are directed toward investigation into new active ingredients, formulations, and delivery systems for repellents for roles in protection of both humans, livestock and wildlife. A team of university and USDA scientists joined for to investigate repellency of (E)-oct-2-enal, a chemical compound originated in donkey sebum, against adult blacklegged ticks. Results of laboratory filter paper bioassays and video tracking analysis of ticks responding to the test compound indicate (E)-oct-2-enal is a highly effective repellent against the blacklegged tick. This study represents the first report of the repellency of a natural, vertebrate emitted chemical against the blacklegged ticks, the vector of Lyme disease. The work made it possible to develop (E)-oct-2-enal based repellent formulations for practical use in personal protection or tick control products targeting the animal hosts of various tick species.

Technical Abstract: Ticks are medically important, nuisance arthropods found worldwide. Applications of semiochemical-based tick repellents for personal protection and reproductive/reservoir host-targeted tick interventions are understudied. We evaluated the repellency of a semiochemical allomone of donkey sebum, (E)-oct-2-enal, against adult Ixodes scapularis ticks – the most frequent human-biting tick in the United States. Ticks were exposed to 20% solutions of (E)-oct-2-enal or DEET. A filter paper bioassay was applied under laboratory conditions. Behaviour was observed for 10-min and captured with a tracking software. Changes in velocity and peregrination were assessed relative to negative (ethanol) control groups using multivariable robust regression models. Repellent longevity was defined by preventing ticks from crossing the treated surface and was evaluated as time-to-event data with a Cox proportional hazard regression model. Significant reductions in velocity, increases in peregrination, and strong longevity were observed for both repellents. Overall assessment of repellency indexes with a Principal Component Analysis showed that DEET and (E)-oct-2-enal were more effective against male ticks than female ticks. There was no difference in effect on females for each repellent. However, the repellency index for male ticks exposed to (E)-oct-2-enal was significantly greater than DEET. This represents the first report, to our knowledge, of the repellency of a natural, vertebrate-emitted semiochemical against I. scapularis ticks. Work is needed to understand the underlying mechanism of action of semiochemical repellents. The development of (E)-oct-2-enal formulations for practical use in personal protection or reproductive/reservoir host-targeted tick control products warrants further consideration.