Seasonal pattern of host-seeking activity by the human-biting adult life stage of Dermacentor andersoni (Acari: Ixodidae).
Nonremoval drag sampling was conducted in multiple sites in Larimer County, CO, from March to July 2006 to determine the seasonal pattern of host-seeking activity by the human-biting adult life stage of the Rocky Mountain wood tick, Dermacentor andersoni Stiles (Acari: Ixodidae). Four sites, at elevations ranging from 1,790 to 2,470 m, consistently yielded host-seeking ticks. Ticks were active from March until late June; the length of the active period ranged from 84 to 104 d. Based on site-specific linear regression models of increase and decrease in tick host-seeking activity over time, densities of D. andersoni adults were estimated to reach 50% of their peaks between 2 and 11 April, to peak between 21 and 28 April, and to fall below 50% of the peaks between 24 and 27 May. The length of the periods with tick densities exceeding 50 and 75% of the peak was 43-52 and 21-26 d, respectively. Rapid increases in tick numbers in late March to early April followed a stretch of days with daily maximum temperatures exceeding 5 degrees C, whereas rapidly declining tick numbers in mid- to late May were associated with daily maximum temperatures consistently exceeding 20 degrees C and daily minimum relative humidity commonly falling below 20%. Densities of D. andersoni adults exceeded 50% of the peak when daily maximum temperatures were in the 16-19 degrees C range and daily minimum relative humidity was > 20%. Finally, tick seasonality may be adapted to local climatic conditions within Larimer County; site-specific daily maximum temperatures at the time of peak tick host-seeking activity in late April were positively associated with site-specific mean daily maximum temperatures for April.
Eisen
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Department of Microbiology, Immunology and Pathology, Colorado State University, Fort Collins, CO 80523, USA. lars.eisen@colostate.edu
D000818:Animals; D001070:Appetitive Behavior / Q000502:physiology; D001733:Bites and Stings / Q000453:epidemiology* / Q000469:parasitology; D003120:Colorado / Q000453:epidemiology; D003870:Dermacentor / Q000502:physiology*; D005247:Feeding Behavior / Q000502:physiology; D006790:Host-Parasite Interactions; D006801:Humans; D006813:Humidity; D011156:Population Density; D012621:Seasons; D013696:Temperature; D013997:Time Factors