In northern California, Ixodes pacificus nymphs are considered the primary vectors of Borrelia burgdorferi, the etiologic agent of Lyme disease. Mendocino County, located in north coastal California, is ecologically diverse encompassing coastal habitats, moist redwood, Douglas fir and tanoak forests, as well as drier oak woodlands, and chaparral habitats. We sought to determine when questing activity of Ixodes pacificus nymphs peaked in 12 localities throughout inland Mendocino county, how long they were questing, and the prevalence of infection with B. burgdorferi. Bi-weekly non-removal sampling of nymphal ticks was conducted along north-south transects in the dry eastern part of the county and closer to the coast in the west from mid-March 2001 until no nymphs were present in late summer or early fall. Additional nymphs (N > 120 per site) were collected adjacent to these non-removal areas and presence of B. burgdorferi infection was tested by direct immunofluoresence assays. Infection prevalence ranged from 2.1 to 16.4%, while peak nymphal densities ranged from 0.83 to 30.1 nymphs per 100 m2, resulting in a range of 0.04 to 4.9 infected nymphs per 100 m2. In general, peak nymphal densities were reached later and remained within 50% of the peak density longer in the north than in the south, however, infection prevalence did not follow such a gradient. Associations of the density of infected nymphs and duration of questing periods with several biotic and abiotic factors (e.g., topographic exposure, distance to coast, habitat type, evidence of deer, ambient temperature and relative humidity) are described. In conclusion, the risk of human exposure to B. burgdorferi-infected nymphs varied throughout the period of nymphal activity and among sites at any time during that period. Therefore, locally derived risk indices are preferable to broad-scale assessments.
Species 1: Acarina Ixodidae Ixodes pacificus (western black-legged tick)
Keywords: Lyme disease
The ESA 2001 Annual Meeting - 2001: An Entomological Odyssey of ESA