Spatial variation in detachment rates of larval Ixodes ricinus from a common host (Apodemus sylvaticus): an experiment.

Because of their low intrinsic mobility, spatial distribution of Ixodes ticks depends strongly on movement of their hosts, but this may be modulated by the tick's decision to detach in relation to environmental cues. This aspect of host-parasite interactions may substantially contribute to micro-geographic heterogeneity in exposure risk to ticks and tick-borne pathogens, but has so far received little attention. We designed a laboratory experiment to investigate whether environmental factors may affect detachment decisions of Ixodes ricinus in two contrasting environments: a dry, bare environment versus a moisturized, enriched environment. We experimentally infested wood mice (Apodemus sylvaticus) with larval ticks and exposed these alternatingly to the two environments in a cross-over design, controlling for temporal variation. Detached larvae were collected whenever hosts were moved from one type of environment to another. Detachment rates were consistently higher in the dry and bare environment. Furthermore, in both environments, the majority of ticks detached in the afternoon and first part of the night. Our results suggest that environmental factors can alter the detachment probability of I. ricinus larvae from A. sylvaticus, either through direct physical or host physiological cues. We postulate that larval detachment favours distribution throughout the forest understorey rather than centred around places of high rodent site fidelity.