Seasonal dynamics of Amblyomma sculptum in two areas of the Cerrado biome midwestern Brazil, where human cases of rickettsiosis have been reported.

Amblyomma sculptum is a common human-biting tick in Brazil, where it plays an important role as a vector of Rickettsia rickettsii, the agent of the Brazilian spotted fever. Herein, we studied the seasonal dynamics of A. sculptum in an urban area of the Cerrado biome in midwestern Brazil, where human rickettsiosis is endemic. Ticks were collected in two sites located within the campus of Federal University of Goiás. The collections were done by dragging, flagging and visual search. In total, 117,685 ticks were collected, including 100,627 Amblyomma spp. larvae, 10,055 nymphs and 6977 adults of A. sculptum, and one nymph and 25 adults of Amblyomma dubitatum. The highest peak of larvae occurred in June 2018 and in July 2019, whereas nymphs peaked in July 2018 and September 2019. Adults reached their highest numbers in March 2018 and November 2019. These data suggest that A. sculptum develops one generation per year in this urban area of the Cerrado biome in midwestern Brazil. Interestingly, the peak of nymphs occurred during the same period of all confirmed cases of rickettsiosis in Goiás, suggesting a possible relationship between the seasonal dynamics of this tick stage and rickettsiosis transmission in this state.

Binary combinations of thymol, carvacrol and eugenol for Amblyomma sculptum control: Evaluation of in vitro synergism and effectiveness under semi-field conditions.

This study aimed to investigate the in vitro acaricidal effect of thymol, carvacrol and eugenol (binary combinations) and their synergistic effect on unfed larvae and nymphs of Amblyomma sculptum, estimate the cost to prepare a formulation with these compounds, and evaluate the formulations under semi-field conditions against A. sculptum larvae. To evaluate the acaricidal effect of the compounds alone or their binary combinations (1:1 ratio) the larval packet test was performed using six concentrations (0.3125 to 10.0 mg/mL) for larvae and seven concentrations (2.5 to 20.0 mg/mL) for nymphs. The cost to produce 1 L of thymol, carvacrol and eugenol solutions, combined or alone, was estimated. In the semi-field test, formulations were sprayed on Panicum maximum plots experimentally infested with unfed A. sculptum larvae. In the in vitro tests with larvae, a synergistic effect (synergism and moderate synergism) was observed for thymol + eugenol at all concentrations tested, while thymol + carvacrol and eugenol + carvacrol showed a synergistic effect at the concentration of 5.0 mg/mL. In the in vitro tests with nymphs, thymol + eugenol, thymol + carvacrol and carvacrol + eugenol showed a synergistic effect (synergism and moderate synergism) at a concentration of 5.0 mg/mL and higher. Combining the compounds reduced the concentrations required to obtain mortality rate above 95%, resulting in lower costs. Under semi-field conditions, the treatments with thymol + eugenol and carvacrol + eugenol showed efficacies of 63.2% and 42.6%, respectively. We conclude that, depending on the concentrations, the binary combinations of thymol, carvacrol and eugenol have a synergistic acaricidal effect on unfed A. sculptum larvae and nymphs, and under semi-field conditions the associations between thymol + eugenol and carvacrol + eugenol were effective against A. sculptum larvae.

Combination of thymol and eugenol for the control of Rhipicephalus sanguineus sensu lato: Evaluation of synergism on immature stages and formulation development.

The aim of this study was to investigate whether the combination of thymol with eugenol has a synergistic effect on the immature life stages of Rhipicephalus sanguineus sensu lato (s.l.), to evaluate the cost-benefit ratio of using these compounds in combination, and to develop a formulation combining thymol with eugenol with activity on immature stages of R. sanguineus s.l. To evaluate synergism, thymol and eugenol, combined (ratio 1:1) or not, were tested at concentrations of 2.5, 5.0, 10.0, 15.0 and 20.0 mg/mL on unfed larvae and nymphs using a larval packet test, and 0.625, 1.25, 2.5, 5.0 and 10 mg/mL on engorged larvae and nymphs using an immersion test. A cost estimate was calculated to produce 1 L of a solution containing a concentration of thymol and eugenol, combined or not, that could cause a tick mortality rate greater than 95 %. Finally, a formulation was developed, consisting of a micellar dispersion containing polymers (MDP), with thymol + eugenol (1:1), at concentrations of 2.5, 5.0, 10.0, 15.0 and 20.0 mg/mL, and the activity was evaluated on unfed and engorged larvae and nymphs. For unfed larvae and nymphs, concentrations of 2.5 and 5.0 mg/mL and 2.5, 5.0 and 10.0 mg/mL, respectively, presented synergistic effects. In tests with engorged larvae and nymphs, respective concentrations of 0.625, 1.25 and 2.5 mg/mL and 2.5 and 5.0 mg/mL had synergistic effects. The estimated costs for producing a solution of 1 L with efficacy greater than 95 % was $5.97 using only thymol (15 mg/mL), $ 5.93 using only eugenol (15 mg/mL), and $ 3.97 using thymol + eugenol (1:1 - 5,0 mg/mL). In tests with MDP, the combination of thymol + eugenol resulted in a mortality rate higher than 95 % at concentration of 10 mg/mL for unfed and engorged larvae and nymphs. Thus, the combination of thymol + eugenol, depending on the concentration, has synergistic effects and this combination lowers the cost for the active ingredients thymol and eugenol. The combination of thymol + eugenol in MDP had acaricidal activity against immature life stages of R. sanguineus s.l.