Efficacy profile of Cypermethrin and Chlorpyrifos based acaricides on Rhipicephalus microplus control on cattle in the rearing phase, naturally infested and exposed to tick fever agents in central Brazil

The objective of this work was to evaluate the efficacy of two cypermethrin- and chlorpyrifos-based acaricides in controlling Rhipicephalus microplus in a naturally infested bovine herd and in in vitro tests, as well as to monitor the animals for tick fever. Male bovines in the rearing phase were used, with 30 Brangus and 30 Nellore animals naturally infested. The groups were composed as follows: 15 Nellore treated, 15 Nellore control, 15 Brangus treated and 15 Brangus control. Every 18 days, the animals were monitored for tick count, acaricide treatment, weight, blood pack cell volume, and clinical signs. For in vitro tests, the larval packet test, adult immersion test and DNA amplification for tick fever diagnosis were performed. In the first animal treatment period, product 1 (cypermethrin, 15 g + chlorpyrifos, 25 g + citronellal, 1 g) was used; in the second period, product 2 (cypermethrin, 15 g + chlorpyrifos, 30 g + fenthion, 15 g) was used. In Brangus animals, the mean efficacy was 35.1% and 95.8% in the first and second periods, respectively, for the same animals. For Nellore animals, the efficacy in periods one and two was 51% and 97.1%, respectively. The in vitro results showed efficacy above 95% for the two challenged acaricides. The Brangus animals showed a high production of ticks associated with the presence of tick fever agents, which could generate risks for the disease's enzootic stability