Variations in Population Density, Movement, and Rickettsial Infection Rates in a Local Population of Dermacentor variabilis (Acarina: Ixodidae) Ticks in the Piedmont of Georgia 1

Adult Dermacentor variabilis ticks studied from 1978 through 1981 in an area with a high incidence of Rocky Mountain spotted fever in Georgia were found to begin questing in late March to mid-April. Three population peaks occurred between March and September (the final peak occurring in late June), indicating that a 1-year life cycle occurs in the area. The ticks were found to occur nonrandomly within all types of habitats, forming clusters which shifted considerable distances annually. Infection rates with rickettsiae-like organisms varied from 0.3 to 1.1%. No significant difference was found in infection rates of ticks from differing habitat types or months of a season, but a significant difference was noted between succeeding years. Annual changes in infection rates combined with shifting clusters of questing ticks may explain the sporadic occurrence of human infection with spotted fever within restricted local areas in Georgia.