Ixodes scapularis Is the most susceptible of the three canonical human-biting tick species of North America to repellent and acaricidal effects of the natural sesquiterpene, (+)-nootkatone

Authors: SIEGEL, ERIC - University Of Massachusetts; XU, GUANG - University Of Massachusetts; Li, Andrew; PEARSON, PATRICK - University Of Massachusetts; ELMAN, NOEL - Gearjump Technologies, Llc; D'HERS, SEBASTIAN - Institute Technology Of Buenos Aires (ITBA); MATHER, THOMAS - University Of Rhode Island; RICH, STEPHEN - University Of Massachusetts

Submitted to: Insects
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/19/2023
Publication Date: 12/22/2023
Citation: Siegel, E.L., Xu, G., Li, A.Y., Pearson, P., Elman, N., D'Hers, S., Mather, T.N., Rich, S.M. 2023. Ixodes scapularis Is the most susceptible of the three canonical human-biting tick species of North America to repellent and acaricidal effects of the natural sesquiterpene, (+)-nootkatone . Insects. https://doi.org/10.3390/insects15010008.
DOI: https://doi.org/10.3390/insects15010008

Interpretive Summary: Ticks are responsible for transmitting several disease agents to humans and animals, including those causing Lyme disease and Rocky Mountain spotted fever. Human protection from tick bites relies on personal protection tactics for preventing or minimizing tick feeding. Most published repellent studies have focused immature stages, particularly nymphs, of various tick species while adult ticks are also often found on humans. USDA ARS scientists joined force with researchers from university and private company to investigate the repellency of nootkatone, a chemical compound found in natural sources like grapefruit oil, against adult ticks of the three most abundant tick species in the northeastern United States. Females of the American dog tick, the blacklegged tick, and the lone star tick were repelled by nootkatone at different concentrations. Blacklegged ticks were most susceptible to this compound, not only being repelled at very low nootkatone concentrations but also experiencing significant mortality when checked 24 hours after exposure. American dog ticks and lone star ticks required much higher concentrations to repel and were not killed by the brief exposures. These results indicate that nootkatone may be used in a dual action killing/repelling role against adult ticks, with particularly strong effects against blacklegged ticks. The results obtained from this study are of interest to researchers and professionals who work in the field of human and animal health, particularly in repellent development and vector control.

Technical Abstract: Ticks are vectors of many human and animal zoonotic disease agents causing significant global health and economic strain. Repellents and acaricides are integral to the capacity for personal protection from tick bites. Nootkatone, a naturally occurring sesquiterpene found in the Alaskan cedar tree, grapefruit, and other sources, has been documented to be a potent acaricide. Research has also noted repellent effects against some tick species. Our aim in the present study was to investigate this effect on Ixodes scapularis, Dermacentor variabilis, and Amblyomma americanum adult ticks in an in vitro, vertical filter paper bioassay with synthetic, high purity (+)-nootkatone. (+)-Nootkatone showed compelling tick repellency, but median effective concentrations (EC50) significantly differed between species. I. scapularis were repelled at very low concentrations, (EC50 = 0.87 ± 0.05 µg/cm2). Higher concentrations were required to repel D. variabilis (EC50 = 251.50 ± 11.52 µg/cm2) and A. americanum (EC50 = 2313.44 ± 178.72 µg/cm2). Significant post-exposure mortality, assessed 24 hours after repellency trials, also was observed with I. scapularis but was absent entirely with D. variabilis and A. americanum. These tests show that nootkatone has a promising dual-action personal protection capacity against I. scapularis adult ticks, which should be further investigated in more natural environments and in the presence of host cues.