HOST-SEEKING BEHAVIOR OF ADULT IXODES-PACIFICUS (ACARI, IXODIDAE) AS DETERMINED BY FLAGGING VEGETATION

Diurnal host-seeking by adults of the western black-legged tick, Ixodes pacificus Cooley & Kohls in relation to vegetative habitat type and meterological factors was investigated at a coastal and an inland site in northern California. Host-seeking behavior and relative tick abundance were determined with a tick drag method from late fall to midwinter 1987-1988. At the inland site, tick abundance usually was significantly greater in chaparral-grassland ecotones than in adjoining dense chaparral on the south-facing slope of a mountaintop, whereas both of these vegetative types produced significantly fewer ticks on a north slope compared with a contiguous south-facing slope. There was no evidence for an association between tick abundance and plant species within ecotonal chaparral. Multiple regression analyses revealed that tick abundance in ecotonal chaparral at the inland site and in grassland at the coastal site was not associated consistently with either ambient temperature or relative humidity. Compared with the inland site, ticks were considerably more abundant at the coastal site where sampling occasionally yielded more than 100 ticks per 100 drag samples. The incidence of infection with Borrelia burgdorferi Johnson, Schmid, Hyde, Steigerwalt & Brenner, the etiologic agent of Lyme borreliosis, in adult ticks collected in the morning (1.5%) versus afternoon (2.2%), and in male (1.3%) versus female ticks (2.5%), at the coastal site in winter was similar.