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: 2/18/2025
Publication Date: N/A
Citation: N/A

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 and nuisance arthropods found worldwide. The applications for semiochemical-based tick repellents in personal protection and interventions targeting reproductive/reservoir hosts are understudied. This research evaluated the repellent effects of an allomone isolate of donkey sebum, (E)-oct-2-enal, against adult Ixodes scapularis ticks – the most frequent human-biting tick in the United States. A laboratory filter paper bioassay was used to expose ticks to 20% solutions of (E)-oct-2-enal and DEET. Behavior was observed for 10 min and quantified with a behavior tracking software. Changes in movement speed and peregrination were assessed relative to negative controls (exposed to ethanol). Repellency 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. The effects of (E)-oct-2-enal presence on repellency, movement speed, and peregrination were stronger or comparable to DEET. Significant reductions in movement speed, increases in peregrination distances, and strong repellency were observed in ticks exposed to either DEET or (E)-oct-2-enal. Repellency was stronger against male ticks than female ticks for both (E)-oct-2-enal and DEET. This work represents the first report, to our knowledge, of the repellency of a natural, vertebrate emitted semiochemical against I. scapularis ticks. Future work is needed to understand the underlying mechanism of action and development of (E)-oct-2-enal formulations for practical use into personal protection or reproductive/reservoir-host targeted tick control products.