Efficacy of imidacloprid/permethrin and fipronil/(S)–methoprene combinations against Haemaphysalis longicornis ticks evaluated under in vitro and in vivo conditions

Abstract

Haemaphysalis longicornis is one of the most important ticks infesting a wide range of mammals including dogs in Japan. H. longicornis is recorded to be a vector of, for example, Babesia gibsoni. It was the aim of the study presented here to evaluate the efficacy of imidacloprid/permethrin and fipronil/(S)–methoprene against larval, nymphal and adult stages of H. longicornis under in vitro as well as in vivo conditions. In the in vitro part of the study, ticks showed avoidance behaviour to imidacloprid/permethrin–treated filter papers. The onset of acaricidal efficacy in the imidacloprid/permethrin group was recorded earlier than in the fipronil/(S)–methoprene group. In the in vivo experiment three beagles per group were treated with either imidacloprid/permethrin, fipronil/(S)–methoprene or left untreated. Each dog was infested with 30 adult female H. longicornis. Ticks were place on a shaved area of skin of the treated dogs and behaviour of the ticks was recorded as before. After 3 h all ticks were removed and placed in Petri dishes. Ticks were further examined until day 4 post–treatment (p.t.). All ticks recovered from the untreated dogs survived. At 4 h p.t. (1 h post–removal) 40 of the 90 ticks exposed to the imidacloprid/permethrin treatment and 25 of the 90 ticks in the fipronil/(S)–methoprene–treated group were found dead. At day 1 p.t., 61 ticks in the imidacloprid/permethrin– and 81 ticks in the fipronil/(S)–methoprene–treated group were recorded dead. At the final examination day 4 p.t., all 90 ticks were found dead in the imidacloprid/permethrin group, while five ticks remained alive in the fipronil/(S)–methoprene group.