Host-seeking of blacklegged tick (Acari: Ixodidae) nymphs and adults at the woods-pasture interface.

ABSTRACT

To clarify the risk of pastured livestock for exposure to Ixodes scapularis Say (Acari Ixodidae), we estimated the host-seeking activity of nymph and adult blacklegged ticks at the woods-pasture interface on horse farms in Maryland. Parallel linear transects of 100 m length and 1 m width were sampled repeatedly in pastures and adjacent woodland locations during periods of nymph (early summer) and adult (fall and spring) host-seeking activity. Data collected over two successive years indicated that adults were most abundant in ecotonal vegetation at the wood's edge, median values of 6.4 and 2.2 ticks per 100 m2 sample during fall and 1.2 and 0.5 ticks per 100 m2 sample for spring periods. Nymphs were most abundant in the shallow woods location, median values of 4.2 and 35 ticks per 100 m2 sample, followed by the deep woods and wood's edge locations. Host-seeking nymph and adult black-legged ticks also were collected repeatedly in pasture vegetation, median values ranging from 0.2-0.8 ticks per 100 m2 sample, with a progressive decrease in abundance from the fenceline into pasture. Adults and nymphs both were uncommon more than 5 m into pastures, where only two adults and one nymph were captured in 84 (fall and spring) and 24 (summer) 100-m2 samples, respectively. Levels of adult and nymph host-seeking in pasture vegetation were spatially correlated with tick abundance in adjacent woodlands when ticks were numerous; this condition presumably reflects a spillover of ticks from the woodlands-based population. These findings expand knowledge of black-legged tick host-seeking behavior and establish a basis for the exposure of pastured livestock to nymphs and adults.