Do the level of energy reserves, hydration status and <i>Borrelia</i> infection influence walking by <i>Ixodes ricinus</i> (Acari: Ixodidae) ticks?

<i>Ixodes ricinus</i> horizontal movement within a humidity gradient and the influence of infection by <i>Borrelia burgdorferi</i> sensu lato (s.l.) on tick walking were investigated. Nymphs were placed within an arena containing a humidity gradient ranging from 45 to 95% relative humidity (RH). After 1 h of acclimation at 70% RHticks were released so that they could either stay, or walk towards either the wet or the dry end. Their position was recorded 2 h post-release. Fat content was quantified and <i>Borrelia</i> infection was detected using real-time PCR and PCR followed by Reverse Line Blotting. Among the 1500 ticks tested, 29·85% were infected. More low- fat nymphs walked inside the arena than high-fat individuals. When nymphs walked, more low-fat ticks walked towards wetter than drier air, whereas more high-fat individuals walked towards drier than wetter air. Among high-fat nymphs, a lower proportion of <i>Borrelia</i>-infected ticks walked inside the arena compared to uninfected individuals, as though spirochetes manipulated their arthropod vector to stay. However, <i>Borrelia</i> infection had no effect on walking direction towards the dry or the wet end. Hence, it appears that I. ricinus nymphs walk horizontally over short distances within a humidity gradient depending on both energy resources and <i>Borrelia</i> infection.