A Novel Ex Vivo Bioassay Suggests DEET is an Effective Repellent of Rhipicephalus Sanguineus1

Abstract Ticks are vectors that pose a threat to public health. N,N-diethyl-3-methylbenzamide (DEET) is commonly applied as a repellent to prevent attachment of ticks to humans and animals. Typical commercially available repellents contain between 5–100% DEET. Lower concentrations of DEET may be necessary to minimize potential health risks associated with DEET. To characterize the repellency of low concentrations of DEET, we performed an in vitro vertical bioassay, and developed a novel ex vivo vertical bioassay using porcine skin for use with the adult brown dog tick, Rhipicephalus sanguineus (Latreille) (Acari: Ixodidae). DEET applied at concentrations of 0.19% in vitro and 12.5% ex vivo immediately after application, and at 0.38% in vitro and 40% ex vivo at 4 h after application, repelled over 90% of ticks. In both in vitro and ex vivo assessments, and at both 0 and 4 h post application, the repellency against female ticks was similar to that against male ticks. This study demonstrates that concentrations of DEET lower than those in commercial repellents may provide sufficient repellency when potential tick exposure occurs shortly after application. Additionally, the development of a porcine ex vivo bioassay provides an alternative assessment tool for future repellency studies.