Population growth rates for Amblyomma americanum (Acari: Ixodidae) on Bos indicus, B. taurus and B. indicus x B. taurus cattle.

Densities of Amblyomma americanum (L.) on Bos indicus, B. taurus and B. indicus X B. taurus cattle are compared over a 3-year period, and the growth rate (rate of increase or decrease) of parasitic tick populations on each cattle genotype is estimated. Average log10 densities of parasitic A. americanum larvae are significantly (P = 0.05) lower on B. indicus cattle than on B. taurus and B. indicus XB. taurus cattle. Average log densities of nymphal and adult ticks on B. taurus cattle are significantly higher than on B. indicus cattle but neither cattle genotype differs in this regard from B. indicus X B. taurus cattle. Estimated annual tick population growth rates (log10) for parasitic A. americanum are positive on B. taurus cattle (+0.84 larvae, +0.09 nymphs, +0.22 adults calf-1 year-1), but are negative on B. indicus (-0.18 nymphs, -0.14 adults calf-1 year-1) and B. indicus X B. taurus cattle (-0.45 larvae, -0.24 nymphs, -0.14 adults calf-1 year-1). Populations of parasitic larvae were not detected on B. indicus cattle.