Stepwise regression analysis was used to determine the predictive relationship between the numbers of each life stage of Amblyomma americanum (Acari: Ixodidae) attached to each of 20 arbitrarily defined body areas and the total number of attached ticks per cow (tick burden). Regressions of tick burden (Y) on the number of ticks (X) attached to the body areas selected on the basis of stepwise regression (i.e., the head, ears, neck, brisket, udder, and escutcheon for larvae; the same areas as for larvae plus the rear flank and dewlap for nymphs; and the dewlap, brisket, foreleg, foreflank, udder, escutcheon, rear leg, and rear flank for adult males and females) resulted in the following density estimators for each life stage. Larvae: Ŷ = 1.081X + 1.477; nymphs: Ŷ = 1.280X + 2.866; males: Ŷ = 1.174X + 0.537; and females: Ŷ = 1.196X + 0.792. More than 95% of observed values for tick burden were within the 95% confidence interval for each Ŷ. On the basis of estimates of the population mean and variance for each life stage, and depending upon the required level of precision, estimation of the mean tick burden in a herd of 30 cows required examination of from 1 to 29 cows.
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Barnard et al. (1985) studied this question.