Population growth rates forAmblyomma americanum (Acari: Ixodidae) onBos indicus,B. taurus andB. indicus x B. taurus cattle

Densities ofAmblyomma americanum (L.) onBos indicus, B. taurus andB. 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 parasiticA. americanum larvae are significantly (P=0.05) lower onB. indicus cattle than onB. taurus andB. indicus x B. taurus cattle. Average log densities of nymphal and adult ticks onB. taurus cattle are significantly higher than onB. indicus cattle but neither cattle genotype differs in this regard fromB. indicus x B. taurus cattle.Estimated annual tick population growth rates (log₁₀) for parasiticA. americanum are positive onB. taurus cattle (+0.84 larvae, +0.09 nymphs, +0.22 adults calf^–1 year^–1), but are negative onB. indicus (–0.18 nymphs, –0.14 adults calf^–1 year^–1) andB. 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 onB. indicus cattle.