IN VIVO TEST METHOD for REPELLENTS against the HARD TICK, IXODES RICINUS (ACARI: IXODIDAE), MAIN VECTOR of LYME BORRELIOSIS and TBE in EUROPE

Abstract:
The present paper describes a test procedure with human volunteers used for a comparative investigation of tick repellents. Eight commercially available repellents were tested against the tickIxodes ricinus (L.) and several test criteria described. Ticks were placed on a copper plate situated on an arm or leg treated with repellent. While the arm or leg was kept vertically, it was observed whether or not a tick entered treated skin and walked a distance of at least 5 cm. No repellent was able to prevent more than 50% of the ticks from entering repellent-treated skin. Two repellents prevented >90% of the ticks from walking over the skin. Taking this as the test criterion, the other six products either repelled lower proportions of the ticks or showed no repellent effect at all. In the majority of repellents, ticks that managed to cross treated skin walked predominantly downwards. This behavior was contrary to the control, in which ticks preferred to walk upwards, and might be indicative of a somewhat weaker repellent effect. Only one of the products tested showed no sign of repellency at all. The described procedure thus proved able to discriminate repellencies of a range of products and may additionally be used for dose-efficacy studies.