First report of the repellency of 2-tridecanone against ticks

2‐Tridecanone and 2‐undecanone are both found naturally in the trichomes of wild tomato plants and are important in plant resistance to herbivory. 2‐Undecanone is the U.S. Environmental Protection Agency (EPA)‐registered active ingredient in the commercially available arthropod repellent, BioUD^®. The goal of this study was to examine the tick repellency of 2‐tridecanone. Two‐choice bioassays were conducted using 8% 2‐tridecanone vs. the repellent carrier (absolute ethanol) and compared with two‐choice studies using 8% 2‐undecanone vs. absolute ethanol. Unfed, host‐seeking adult (mixed sex) Amblyomma americanum (L.) (Acari: Ixodidae) and Dermacentor variabilis Say (Acari: Ixodidae) were used to evaluate repellency and time to repellent failure at room temperature. The present study shows in filter paper assays (0.63 mg test compound/cm²) that 2‐tridecanone was 87% repellent to A. americanum at 12 h after application, but had no statistically significant repellency at 15 h and 24 h, and was 72% repellent to D. variabilis at 15 h, but had no statistically significant repellency at 24 h. By contrast, 2‐undecanone was 74% and 75% repellent to A. americanum and D. variabilis, respectively, at 2 h after application, but no statistically significant repellency was noted at 2.5 h and 3 h. In two‐choice assays on cheesecloth, 2‐tridecanone at 0.25 mg/cm² was 85% repellent to A. americanum 6 h after application, demonstrating its potential use as an arthropod repellent that can be used on clothing without the need for formulation. No statistically significant repellency was found at 9 h or 12 h. The potential use of 2‐tridecanone as a tick repellent is discussed.