VEGETATIONAL ASSOCIATIONS OF HOST-SEEKING ADULT BLACKLEGGED TICKS, IXODES-SCAPULARIS SAY (ACARI, IXODIDAE), ON DAIRY FARMS IN NORTHWESTERN WISCONSIN

As a measure of the risk for exposure to Lyme disease, we estimated th e distribution of host-seeking adults of the blacklegged tick, Ixodes scapularis Say, on daily farms in Barren County in northwestern Wiscon sin. Vegetation ecotypes that were common to 18 farms that were repres entative of the county were surveyed by flag sampling. Tick prevalence and abundance, which were similar during fall and spring periods, wer e very lawn in farmhouse yards and forage croplands; only a single mal e was collected from 17 lawns. Sampling of 18 pastures with lactating cows also yielded only a single I. scapularis. In contrast, I. scapula ris adults were captured in 9 of 37 samples from 18 pastures with heif ers and dry cows; in those pastures, ticks were associated with woods and secondary vegetation or margins of pastures adjacent to woodlands. Blacklegged ticks were most prevalent and numerous in ungrazed woodla nds; adults were captured in 27 of 53 samples on 13 of 15 farms, parti cularly when evidence of white-tailed deer, Odocoileus virginianus (Zi mmermann), was apparent. The risk of encountering adult blacklegged ti cks on dairy farms in Barren County, Wisconsin is therefore greatest i n woodlands habitat. The presence of adult ticks in pastures with heif ers and dry cows establishes an ecological basis for the exposure of d airy cattle to adult I. scapularis. Pastures with lactating cows, farm house yards, and forage croplands represent negligible risk.