Compostos botânicos e químicos na repelência e controle de Amblyomma sculptum

Abstract

Amblyomma sculptum is a tick of medical and veterinary importance, associated with the transmission of Brazilian spotted fever. The use of repellents is an essential strategy to minimize contact between ticks and hosts, thereby reducing the risk of pathogen transmission. N,Ndiethyl-meta-toluamide (DEET) is widely used as the gold standard repellent against arthropods, but its continued use raises concerns regarding toxicity and environmental impact. Therefore, botanical compounds have been investigated as promising candidates to replace or reduce dependence on DEET in repellent formulations. In addition to preventive strategies, chemical control using acaricides is still widely employed. However, the frequent use of conventional classes has led to the selection of resistant strains, reinforcing the need to search for new molecules with distinct modes of action, such as fluralaner, an isoxazoline with systemic activity and prolonged efficacy. This study evaluated the repellent activity of isolated botanical compounds and their combinations with DEET through laboratory and field bioassays. Three types of experimental assays were conducted: (i) contact tests on Petri dishes, (ii) olfactory assays using a Y-tube olfactometer, and (iii) field tests with human volunteers. In the initial phase, DEET, eugenol, methyl eugenol, and 1,8-cineole (at 1% and 2%) were tested, along with combinations of DEET + eugenol and DEET + methyl eugenol, against A. sculptum nymphs. In the Petri dish assay, eugenol 1% and the combination DEET 7% + eugenol 1% achieved average repellency rates of 93.3% and 98.3%, respectively. Based on these results, these formulations were selected for field tests, where volunteers walked through tick-infested areas and the attachment of parasites was recorded every 20 minutes over a 2-hour period. The combination DEET 7% + eugenol 1% provided the highest level of protection (88.5%), followed by DEET 7% (82.5%), while eugenol alone showed reduced efficacy after 20 minutes. In the second phase, the botanical compounds eugenol, nootkatone, carvacrol, and thymol were tested at 5%, as well as the combination of eugenol (2.5%) + nootkatone (2.5%), with DEET (7%) used as a positive control. In contact assays, carvacrol and nootkatone (5%) exhibited repellency above 90%, while the eugenol + nootkatone combination reached 100% repellency at certain time points. In the olfactory assay, the combination was avoided by 72.22% of the nymphs, performing similarly to DEET. In field tests, this association showed an average repellency of 88.2% over 120 minutes, peaking at 94.5% in the first 20 minutes. Finally, the acaricidal activity of fluralaner was evaluated against larvae, nymphs, and unfed adults, as well as engorged females of A. sculptum, through immersion tests. The compound showed high efficacy across all stages tested, with 100% mortality at higher concentrations and complete inhibition of oviposition in engorged females. These findings highlight its potential as a complementary tool in the integrated management of ticks.