TEMPORAL AND SPATIAL-DISTRIBUTION OF IXODES-PACIFICUS AND DERMACENTOR-OCCIDENTALIS (ACARI, IXODIDAE) AND PREVALENCE OF BORRELIA-BURGDORFERIIN CONTRA-COSTA COUNTY, CALIFORNIA

The seasonal activity and spatial distribution of adult and immature I xodes pacificus Cooley & Kohls and Dermacentor occidentalis Marx were determined along trails and on hillsides in two parks in Contra Costa County, CA. I. pacificus and D. occidentalis adults were most numerous in January and May, respectively. Adult ticks were significantly more abundant along heavily vegetated trails than on open grassy hillsides , and on the uphill versus the downhill side of trails. Five species o f rodents were captured, and numbers of 1. pacificus and D. occidental is larvae per rodent were highest in May-June and July, respectively. Few nymphs were recovered either by flagging or from captured rodents. An average of 2.2 and 2.8% of the I. pacificus adults collected from the two parks were infected with the Lyme disease spirochete, Borrelia burgdorferi Johnson, Schmid, Hyde, Steigerwalt & Brenner. The greates t risk of contracting Lyme disease from adult I. pacificus in these tw o Contra Costa County parks is during the winter months, especially wh ile hiking near the uphill side of trails.