A blinded controlled laboratory study was conducted to assess the acaricidal efficacy of the fipronil/permethrin spot-on formulation (Frontline Tri-Act®, Boehringer Ingelheim) against Haemaphysalis longicornis ticks. Fourteen healthy dogs were included in this study. Dogs in Group 1 served as untreated controls while dogs in Group 2 were treated with Frontline Tri-Act on Day 0 at the minimum recommended dose of 0.1 mL/ kg, corresponding to 6.76 mg/kg fipronil, and 50.48 mg/kg permethrin. All dogs were experimentally infested with 50 viable unfed female H. longicornis ticks on days-2, 7, 14, 21, and 28. Thumb counts were per- formed at 24 hours post-infestations on Days 8, 15, 22, and 29, and ticks were removed and counted at 48 hours post-treatment (on Day 2) and after each tick infestation on Days 9, 16, 23, and 30. Acaricidal efficacies for 24h thumb-counts were 100%, 98.8%, 91.7%, and 84.4% on Days 8, 15, 22, and 29, respectively. Efficacies of 98.1%, 100%, 100%, 98.1%, and 94.7% were determined based on removal counts performed on Days 2, 9, 16, 23, and 30, respectively. There were significant differences of the number of live ticks between treated and control group at each time-point (p <0.005). A single topical administration of the combination of fipronil plus permethrin was highly effective against H. longicornis for four weeks.
