Elmer H. Ahrens

Efficacy of amitraz (Taktic® 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 each 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, animals were restrained in stanchions placed individually inside 3.3 x 3.3 m2 stalls 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 that concentrations of amitraz in the vat were 7.6 to 13% lower than the targeted concentrations of 0.010, 0.015, 0.020, and 0.025% active ingredient (AI) for dilutions prepared according to instructions on the manufacturers 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 each of the four observed concentrations (0.0088, 0.0131, 0.0174, and 0.0231% AI) of amitraz was excellent (> 99% control). However, the rapid detachment of all ticks from an animal within a few hours after treatment with amitraz, that has been frequently observed, was not pronounced in the present study. 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 the vat was undisturbed for six weeks, intense agitation was required to re-suspend the active ingredient.

Efficacy of sprays of amitraz against Boophilus ticks on cattle

Abstract Cattle infested with all parasitic life-stages of Boophilus microplus (Canestrini) and B. annulatus (Say) were sprayed with 0.0125 or 0.025% active ingredient (AI) Amitraz. The detachment pattern of engorged or partially engorged females indicated that both concentrations of Amitraz caused premature detachment, with at least 90% of all females detaching within 24 h post-treatment. A large portion of the females collected during the first 24 h post-treatment were not fully engorged. The 2 tick species were equally sensitive to both concentrations tested. At 0.0125%, control of Index of Reproduction (IR) of B. annulatus was 98.9% while control of B. microplus was 97.8%. At 0.025% control of IR was 99.2 and 98.0% for B. annulatus and B. microplus , respectively. Amitraz adversely affected size and oviposition of females and the hatchability of eggs laid by treated females. Based on known detachment intervals of females after infestation, it appeared that Amitraz-treated animals were protected against larval reinfestation of both species for ca. 7 days at 0.0125% and for ca. 10 days at 0.025%.

Efficacy of freshly mixed coumaphos suspensions adjusted to various pH levels for treatment of cattle infested with Boophilus annulatus (Say) (Acari: Ixodidae)

Abstract Reductive dechlorination of coumaphos results in the formation of a highly toxic material, potasan, but lower pH (≤ 5.5) of the liquid containing coumaphos may eliminate this degradation process. However, the effects of lower pH on the rapid settling of coumaphos particles and on the efficacy of the pesticide are not known. Three suspensions were made from a freshly mixed stock solution of a flowable formulation of coumaphos at 0.125% active ingredient at pH values of 6.7, 5.5, and 4.5. Coumaphos particles were observed to remain well suspended in all pH treatments before, during, and for up to 1 h after applications were made on tick infested cattle, suggesting that there was no break in any of the coumaphos suspensions. Likewise, observations on the behavior of each of the animals (both treated and untreated) appeared to be similar and uniform across all groups, suggesting that the lowering of the pH would not cause any noticeable adverse reaction in the treated animals. Data obtained from the coumaphos suspensions at each of the three pH treatments (pH 6.7, 5.5, and 4.5) against Boophilus annulatus (Say) resulted in control of the index of reproduction (IR) that ranged from 94.4 to 96.5%, indicating that pH had little effect on the efficacy of the acaricide. Results also indicated that the pH of coumaphos suspensions had little effect on engorgement weights (range 270–280 mg), egg mass weights (range 88–100 mg), or percent hatch of eggs (range 57–71%) of females that survived the treatments. Therefore, we concluded that coumaphos suspensions with a pH as low as 4.5 would have no observable adverse effect on the rapid settling of coumaphos particles in suspension, cause no noticeable adverse reactions in treated animals, and remain highly efficacious against B. annulatus .