There is limited information on the resistance to acaricidal drugs of the cattle tick Rhipicephalus microplus in the Lower Amazon region. Thus, we aimed to determine the efficiency of three widely used acaricide products (Amitraz, Cypermethrin, and Deltamethrin) in the control of this tick species. The adult immersion test was used on engorged female ticks sampled on farms in the Lower Amazon region, Brazil. For the test, homogeneous batches of 10 engorged females were placed in Petri dishes and immersed in the tested acaricidal drugs, using four replicates of each acaricide and three replicates as a negative control, immersed in distilled water. The acaricides were diluted as recommended by the manufacturers, and the ticks were submerged for five minutes. Mortality of engorged females, production of eggs, and percentage of larval hatching were evaluated. Tick mortality was 2.5%, 7.5%, and 0% for Amitraz, Cypermethrin, and Deltamethrin, respectively. The percentage of larval hatching was 53.7% for Amitraz, 88.7% for Cypermethrin, and 80.0% for Deltamethrin. As recommended by the FAO, for the acaricide to be considered effective, it must have a control rate ≥95%. Among the tested acaricides, Amitraz showed an efficacy of 90.5%, Cypermethrin 10.4%, and Deltamethrin 26.6%. Ticks from the lower Amazon showed marked resistance to Cypermethrin and Deltamethrin and mild resistance to Amitraz. This is the first report of acaricidal resistance in the region.

Dermacentor nitens (tropical horse tick) is a tick species commonly found parasitizing horses and other equids in the Amazon region, causing economic losses. Currently, tick control is based on chemical acaricides, usually in a power formulation for topical use. However, its indiscriminate use results in the emergence of resistant tick lineages. Several plant compounds have been tested for their acaricide activity. In the Amazon, several plants are used for oil extraction, resulting in the production of solid residue (waste) that may contain chemical molecules with biological activities. Thus, we aimed to test the in vitro acaricidal potential of the ethanolic extract of the industrial residue of andiroba (Carapa sp.) against D. nitens. In a larval immersion test (LIT), D. nitens larvae were tested with 2.5%, 5%, and 10% andiroba extract concentrations in three replicates. Subsequently, the envelopes were kept in a BOD chamber (28 °C ± 1 °C; 80% ± 5% humidity) for 24 h. At the end of this period, live and dead larvae were counted, and efficiency was calculated from the mortality rate caused by the extract and corrected by the Abbot formula. In the three repetitions, the andiroba extract at a concentration of 5% caused the death of 100% of the larvae. At concentrations of 2.5% and 10%, they caused the death of, respectively, 12.38% (±3.5%) and 69.79% (±7.98%) of the larvae. These results indicate that the extract from the industrial residue from the production of andiroba oil has acaricidal activity. It is concluded that the solid waste from industrial andiroba oil extraction has the potential for the development of natural acaricides against D. nitens.