Efficacy of amitraz (Taktic (R) 12.5% EC) as a dip for the control of Boophilus microplus (Canestrini) (Acari : Ixodidae) on cattle

Four groups of cattle infested with Boophilus microplus (Canestrini) were e ach dipped in a different concentration of amitraz diluted from a 12.5% EC formulation to determine the efficacy and performance of the product in an 11 400 l dipping vat. except for the period when heifers were dipped, anima ls were restrained in stanchions placed individually inside 3.3x3.3 m(2) st alls within an open-sided barn. The amitraz in the vat was stabilized with hydrated lime to maintain a pH of ca. 12. Analyses of vat samples showed th at concentrations of amitraz in the vat were 7.6 to 13% lower than the targ eted concentrations of 0.010, 0.015, 0.025%, and 0.025% active ingredient ( AI) for dilutions prepared according to instructions on the manufacturer's label. The large quantity of hydrated lime added to the vat (10 kg/1000 l) interfered with the HPLC analysis of vat samples. Therapeutic efficacy of e ach of the four observed concentrations (0.0088, 0.0131, 0.0174, and 0.0231 % AI) of amitraz was excellent (>99% control). However, the rapid detachmen t of all ticks from an animal within a few hours after treatment with amitr az, that has been frequently observed, was not pronounced in the present st udy. Only 47% of the B. microplus detached in the first 4 h post-treatment, and 84% detached within the first 24 h. All of the treatments, except the lowest concentration, provided protection of cattle against re-infestation by B, microplus larvae for 14 days post-treatment. Possibly as a result of the formation of a compact layer of lime and amitraz on the bottom after th e vat was undisturbed for six weeks, intense agitation was required to re-s uspend the active ingredient. (C) 1998 Elsevier Science B.V. All rights res erved.