The efficacy of amitraz against cattle ticks in Tanzania.

The efficacy of amitraz on cattle ticks was assessed by susceptibility tests, spraying and dipping trials. Tests on the susceptibility of three tick species, Rhipicephalus appendiculatus, Amblyomma variegatum and Boophilus decoloratus to amitraz (technical grade-purity 98.6% w/w) showed all 15 tick strains tested to be highly susceptible, with LC50 ranging between 0.001% and 0.03%, and LC99, between 0.01% and 0.07%. Spraying trials were carried out on calves infested with R. appendiculatus, A. variegatum and B. decoloratus. Amitraz wettable powder [as Taktic total replacement (TR)] was tested against B. decoloratus, and amitraz emulsifiable concentrate (as Taktic EC) against the other two species. Both formulations showed instant action, with ticks detaching from the calves between 30 min and 8 h after spraying. More than 50% of the detached engorged females failed to lay eggs. The remainder laid few eggs, and these had a low hatching rate of 0-2%, compared with 90-98% in the controls. The detached nymphs failed to moult, and the males and non-engorged females also detached, were immobilized and finally died. In the dipping trials, cattle heavily infested with ticks (mean tick counts of about 800) were dipped once weekly in amitraz (Taktic TR). Weekly tick counts showed that the reinfestation rate was reduced to zero after the ninth dipping. The results of the three trials complement each other, showing that amitraz is at present effective in the control of African tick species on cattle in Tanzania.