"Can you beat DEET?": Efficacy of DEET-free insect repellents on adult and nymphal Dermacentor variabilis and Amblyomma americanum (Acari: Ixodidae)

Dermacentor variabilis and Amblyomma americanum are ticks of medical and veterinary importance due to their abundance, the attraction to humans, and competence to transmit a variety of pathogens. These traits enable successful zoonotic transmission between animals and humans through feeding at different life stages. The Center for Disease Control and Prevention (CDC) recommends using a repellent containing 20-30 percent DEET to prevent exposure to infected ticks. However, studies have demonstrated possible negative effects of DEET-containing products especially in children. Therefore, there is a need to develop alternative products to repel ticks. This laboratory study compared the effectiveness of 2 comercial repellents, and 2 essential oil mixtures (a lemon eucalyptus oil repellent, a picaridin repellent, a cedarwood oil mixture, and a citronella oil mixture) with a standard 25% DEET repellent and a water control. We hypothesized that all repellants would be equally effective against ticks. Adult male and female ticks (N=180 each sex/species) and nymphal ticks (N = 360 each species) were tested in an arena with a repellant barrier that separated the ticks from a CO₂ attractant source. Both D. variabilis and A. americanum adults and nymphs demonstrated a varied response to the products tested with the picaridin repellent and citronella oil mixture slightly outperforming DEET repellent. These results demonstrate that alternatives to DEET may effectively repel ticks under laboratory conditions.