Estimating population size and drag sampling efficiency for the blacklegged tick (Acari: Ixodidae).

Estimates of absolute density were determined over a 5-yr period (1990-1994) for a population of Ixodes scapularis Say located in Westchester County, NY, by mark-release-recapture (nymphs and adults) and removal (larvae) methods. Density estimates for larvae ranged from 5.2 to 16.5/m2 and averaged 11.5/m2. Values for nymphs varied as much as fourfold among successive years, ranging from 0.5 to 2.3/m2 and averaging 1.2/m2, whereas adult density ranged from 0.3 to 0.4/m2, averaging 0.33/m2. Natural mortality of nymphs and adults was measured in experimental cages during population estimation periods, and indicated that survival declined linearly over the short-term and did not significantly influence estimates. Drag sampling efficiency, the proportion of the estimated population obtained in a single sample, averaged 6.3% among all stages. Efficiency was not significantly different among stages and was independent of tick density within a given life stage. The population estimation techniques employed in this study are well suited for use with I. scapularis and can provide data that offer insights into mortality patterns in individual populations.