The aim of this work was to identify the compounds and to investigate the acaricidal activity of the essential oil from the leaves of Lippia sidoides on Rhipicephalus microplus and Dermacentor nitens. The oil was obtained by hydrodistillation and analyzed by gas chromatography (GC/FID) and gas chromatography/mass spectrometry. In total, 15 compounds comprising 99.97 % of the total peak area were identified. The main constituent of the essential oil was thymol (67.60 %). The acaricidal activity was assessed by the modified larval packet test, with oil concentrations of 2.5, 5.0, 10.0, 15.0, and 20.0 μl/ml, and by the female immersion test with concentrations of 10.0, 20.0, 40.0, 60.0, and 80.0 μl/ml. The mortality of the R. microplus and D. nitens larvae was greater than 95 % starting at concentrations of 10.0 and 20.0 μl/ml, respectively. In the test with the engorged females, the L. sidoides essential oil starting at a concentration of 40.0 μl/ml caused a significant reduction (p < 0.05) in the values of the egg mass weight and egg production index. The viability of the eggs was affected in all the treated groups, with significantly lower hatching rates (p < 0.05) in relation to the control group. The control percentages at concentrations of 10.0, 20.0, and 30.0 μl/ml were 54, 57, and 72 %, and reached 100 % at the highest two concentrations (60.0 and 80.0 μl/ml). Therefore, it can be concluded that the essential oil from the leaves of L. sidoides has acaricidal activity on R. microplus and D. nitens.

h i g h l i g h t sOf the 587 populations tested for pyrethroids, 97.44% were resistant. For organophosphates were tested 306 populations and 75.49% were resistant. Into populations resistant to pyrethroids, 91% are heterozygous. The analysis confirmed the serious problem of resistance of Rhipicephalus microplus populations. g r a p h i c a l a b s t r a c t a b s t r a c tThe monitoring of resistance of cattle tick populations in Brazil to the chemical bases in use is largely limited to investigation of the phenotypic profile. There are few studies investigating the role played by the genotypic profile in acaricide resistance in the country. Therefore, the aim of the present study was to carry out molecular characterization and trace out the genetic profile of populations of Rhipicephalus microplus with respect to resistance to the organophosphate and pyrethroid chemical groups. For that purpose, larvae were genotyped belonging to 587 populations for pyrethroids and 306 for organophosphates, using the polymerase chain reaction technique. It was found that 75.49% and 97.44% of the larvae studied showed resistance to the organophosphates and pyrethroids, respectively. Among the populations resistant to pyrethroids, 91.9% were heterozygotes, showing that most of the resistant populations have only one allele responsible for resistance. Therefore, it is possible to conclude that the genotyped populations have high resistance to organophosphates, and even more so to pyrethroids. This information is fundamental for understanding the mechanisms of resistance of R. microplus to acaricides, to enable improvement of control techniques.

The aim of this study was to evaluate the acaricidal activity of eugenol, with different solubilizations and concentrations, on Rhipicephalus microplus and Dermacentor nitens larvae and to determine the lethal time. The study consisted of four experiments, and the mortality was assessed using the larval packet test with adaptations. The mortality observed in the first experiment was 100 % for all the groups treated with eugenol solubilized in different solvents. In the second, the hydroethanolic formulation of eugenol was used, and the mortality rates for R. microplus and D. nitens was 100 % starting from the concentration of 5.0 μl/ml. In the third experiment, the mortality was 100 % for larvae of both R. microplus and D. nitens after 1 h of contact. And in the fourth experiment, the mortality was above 90 % and statistically similar (p > 0.05) for the four methods the test evaluated.

This study aimed at assessing the combined effect of thymol, carvacrol and (E)-cinnamaldehyde on Amblyomma sculptum and Dermacentor nitens larvae. The effects resulting from treatments were evaluated by means of the modified larval packet test. In order to determine the LC50, components of essential oils, the monoterpenes thymol, carvacrol and phenylpropanoid (E)-cinnamaldehyde were individually tested at different concentrations. After determining the LC50, each essential oil component was separately evaluated and then combined with another substance at a 1:1 proportion at the LC50 concentration and at 1/2 and 1/4 of the LC50. For A. sculptum, the lowest LC50 value was obtained for (E)-cinnamaldehyde (1.40 mg/ml), followed by thymol (2.04 mg/ml) and carvacrol (3.49 mg/ml). The same order of effectiveness was observed for D. nitens, with values of 1.68, 2.17 and 3.33 mg/ml, respectively. In the evaluation of component associations of essential oils against A. sculptum larvae, only the combinations between carvacrol and thymol (LC50) and carvacrol and (E)-cinnamaldehyde (1/4 LC50) presented a moderate synergetic effect. In turn, for D. nitens larvae, the combinations between thymol and carvacrol (LC50 and 1/2 LC50) presented a synergetic effect, while the others presented an additive or antagonistic effect. Therefore, it can be concluded that the combination of thymol and carvacrol (LC50) has a moderate synergetic effect against A. sculptum larvae, while thymol, combined with carvacrol (LC50 and 1/2 LC50), has a synergetic effect against D. nitens larvae.

The effects of combinations of the monoterpenes thymol and carvacrol and the phenylpropanoid eugenol in larvae of Rhipicephalus microplus (Canestrini, 1888) (Acari: Ixodidae) and Rhipicephalus sanguineus sensu lato (s.l.) (Acari: Ixodidae) were assessed by the larval packet test. The CompuSyn program was used to make qualitative assessments of the effects (synergistic, additive and antagonistic) of the associations. The effects of all combinations tested against R. microplus larvae were synergistic, with combination indices (CIs) <0.70. When tested against R. sanguineus, eight of the mixtures showed a synergistic effect (CI < 0.70); only the carvacrol + thymol mixture at LC presented a moderate synergistic effect, with CIs between 0.70-0.90. This study is the first to determine the effects of the interactions of these substances in the control of these two tick species. The combinations of carvacrol + thymol, carvacrol + eugenol and thymol + eugenol have synergistic effects in R. microplus and R. sanguineus s.l. larvae.