Diurnal Host Seeking of Adult Pacific Coast Ticks, Dermacentor Occidentalis (Acari: Ixodidae), In Relation to Vegetational Type, Meteorological Factors, and Rickettsial Infection Rates in California, USA

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Abstract
Diurnal host-seeking activities of Dermacentor occidentalis adults in chaparral and grassland were evaluated by flagging vegetation and with CO2 (dry ice)-baited traps in Mendocino Co., California, USA, in 1982–1983. Ecotonal chaparral yielded significantly more ticks by flagging than did chaparral on south-facing slopes, and tick abundance was higher on south-than on north-facing slopes. Ticks did not exhibit any specificity with regard to chaparral plants selected as questing sites. Regression analyses revealed that temperature, relative humidity, and solar radiation, either singly or in combination, usually did not explain a significant amount of the total daytime variation in tick numbers. Flagging demonstrated that adults were aggregated at the chaparral-grassland ecotone and that their numbers diminished markedly within 3–5 m on either side of it. Tick infection rates with rickettsia-like organisms and spotted fever group rickettsiae did not differ significantly by sex or exposure (north- vs. south-facing slopes). An evaluation of the drag method as to efficiency, drag size, and potential impact on localized populations in chaparral revealed that it was reasonably efficient, that drag sizes of 0.46 and 0.92 m2 produced comparable results, and that weekly flagging for 1.5 months did not consistently reduce tick numbers in ecotonal chaparral. In contrast, the CO2-trap method yielded relatively low numbers of ticks in chaparral, ecotone, and grassland (in descending rank), with much variation between samples. Mark-recapture experiments with CO2-baited pitfall traps demonstrated that the effective radius for collecting adults in chaparral was 4 m; 30.5% of 200 ticks released within 0.5–4.0 m of the trap were recovered in 4 h of trapping. Only 4 (2.5%) of 160 ticks released 5–12 m from the trap were recaptured in 12 h of trapping.