Amblyomma sculptum is a relevant tick species from a One Health perspective, playing an important role as a vector of Rickettsia rickettsii, the main agent of spotted fever rickettsiosis in Brazil. In this study, we evaluated the susceptibility of two A. sculptum populations from Goiás state (midwestern Brazil) to different acaricides. The first tick population (GYN strain) originated from an experimental farm, where the ticks are annually exposed to acaricides. The second (PNE strain) was collected in a national park (Emas National Park), where the ticks had not been exposed to acaricides. Immersion tests were conducted with 21-day-old laboratory-reared larvae and nymphs originating from adult ticks collected in the areas mentioned above. The chosen acaricides were two synthetic pyrethroids (cypermethrin and deltamethrin), one organophosphate (chlorfenvinphos), one formamidine (amitraz), and two combinations of pyrethroids and organophosphates (cypermethrin, chlorpyrifos and citronellal; cypermethrin, fenthion and chlorpyrifos). Mortality data were used to determine the lethal concentration (LC) values at which 50%, 90%, and 99% of the ticks died (LC₅₀, LC₉₀, and LC₉₉, respectively), and resistance ratios (RR) were calculated based on the LC values. The RR revealed differences between the acaricide-exposed (GYN) and unexposed (PNE) tick strains. The PNE strain larvae and nymphs were susceptible to all the tested acaricides. The GYN strain larvae were tolerant to cypermethrin, whereas the nymphs were tolerant to deltamethrin, chlorfenvinphos, and the combination of cypermethrin, chlorpyrifos, and citronellal (2 < RR ≤ 10). The GYN strain nymphs were resistant to amitraz (RR > 10). This is the first report of A. sculptum nymphs with resistance to amitraz and tolerance to deltamethrin, chlorfenvinphos, and the combination of cypermethrin, chlorpyrifos, and citronellal.

Background: The first isoxazoline-based acaricide (fluralaner) for the control of Rhipicephalus microplus was introduced onto the market in 2022, initially in Brazil, followed by other Latin American countries. Therefore, it is important to establish laboratory methods to monitor the susceptibility of populations of R. microplus to this molecule and to determine the relationship between the results of laboratory tests and those from field trials. Methods: A larval immersion test (LIT) was performed on 18 populations of R. microplus. The lethal concentration 50 (concentration causing 50% mortality [LC50]) values were calculated to determine the resistance ratios (RRs) of the populations. The lethal concentration 99 (concentration causing 99% mortality [LC99]) values were calculated to determine the discriminating doses (DDs = 2 × LC99). The DDs were applied in tests with the POA (susceptible) and GYN (resistant) strains, as well as in tests with the population that presented the lowest LC50 value (population 14) and with the two populations that presented the highest LC50 value (populations 10 and 16). Finally, we performed field trials with the population that presented the lowest and two highest LC50 values. Results: In the LIT with fluralaner, the LC50 values ranged from 0.144 to 0.481 µg/mL for the 18 R. microplus populations. The mortality rate was 100% in the tests of the DDs in the five populations tested. In the field trials, the efficacy of fluralaner was similar for the three populations of R. microplus tested (populations 14, 10 and 16), with therapeutic efficacy (until day 21) of 100% and persistent efficacy (between days 28 and 42) > 95%. Conclusion: We observed natural variability in the susceptibility of larvae from the different populations of R. microplus that had never been treated with this compound. Despite the observed variability in the in vitro results (LC50), a comparable efficacy of > 90% lasting until day 42 was observed in the field trials. Also, based on the results of the laboratory testing (LC50 and DD) and field trials, we can conclude that there was no resistance to fluralaner in the 18 studied tick populations. Graphical

This study evaluated the repellent activity of the botanical compounds thymol, carvacrol, nootkatone, and eugenol (5%), as well as the combination of 2.5% nootkatone + 2.5% eugenol, against Amblyomma sculptum nymphs under laboratory and field conditions. In contact bioassays, carvacrol and nootkatone showed the highest mean repellency rates (94.5% and 93.7%), followed by thymol and eugenol (90.2% and 87.2%). The combination (nootkatone + eugenol) resulted in 92.8% repellency, with 100% efficacy in some evaluation periods. The repellency of 7% DEET (positive control) was 82.2%. Nootkatone 5% and the combination (nootkatone + eugenol) were also tested in a Y-tube olfactometer, showing repellency rates of 86.1% and 72.2%, respectively, both higher than 7% DEET (69.4%). In field trials, volunteers wore treated socks and walked through an area naturally infested with nymphs. A significant reduction (p < 0.05) in tick counts was observed in the treated groups (about five unfed nymphs) compared to the control (about 40 unfed nymphs). Cumulative efficacy exceeded 85% in both treatments. In the cost simulation, the estimated cost of a 100 mL formulation containing 5% nootkatone was USD 50.8, while the combination (nootkatone + eugenol) presented a cost USD 28.6, representing a 44% reduction with no loss of efficacy in field conditions. These results indicate that all compounds tested showed repellent activity in the laboratory. Nootkatone has high repellent activity, and its combination with eugenol is a promising and more economically viable alternative for tick repellency.

This study evaluated the repellent activity of DEET, eugenol, methyl eugenol, 1,8-cineole, and their combinations against Amblyomma sculptum nymphs through laboratory and field tests. Initially, the botanical compounds were tested individually in Petri dish assays to assess repellent activity over various intervals (1 min to 168 h) at concentrations of 2%. Eugenol and methyl eugenol exhibited the highest average repellent percentages (60 to 90%), with significant effects (p < 0.05) across most evaluation periods, in contrast to 1,8-cineole. Therefore, eugenol and methyl eugenol were selected for combination testing with DEET. The combinations of 7% DEET + 1% eugenol and 7% DEET + 2% methyl eugenol showed the best results, with average repellent efficacy exceeding 85%. The first combination was selected for field evaluation. In this test, volunteers wore treated socks and walked for two hours in a naturally infested area. A significant reduction (p < 0.05) in the number of ticks recovered from the socks was observed in the 7% DEET and 7% DEET + 1% eugenol treatments, with efficacies of 82.5% and 88.5%, respectively, after 120 min. Isolated eugenol showed limited field efficacy, with significant repellent activity (p < 0.05) lasting only 20 min. The results highlight the potential of eugenol and methyl eugenol as repellent compounds, especially when combined with DEET. The field study confirmed the efficacy of the 7% DEET + 1% eugenol.