Efficacy of thyme oil and nano-formulated derivatives against Rhipicephalus sanguineus sensu lato (Acari: Ixodidae)

The brown dog tick, Rhipicephalus sanguineus plays a significant role in transmitting pathogens to humans and animals, necessitating control measures. Given the drawbacks of synthetic chemicals, plant-based alternatives are a promising option for tick management. The present study aimed to evaluate the acaricidal potential of thyme oil (TO) and nano-formulations {thyme oil nano-emulsion (TNE), silver nanoparticles (AgNPs), and thyme nano-emulsion containing silver nanoparticles (TNE- AgNPs)} against R. sanguineus using an adult immersion bioassay. Gas chromatography-mass spectrometry (GC-MS) was used for TO analysis. The UV- visible spectroscopy, transmission electron microscopy (TEM), and particle size were used to characterize the nano-formulations. In addition, the freshly dead ticks were examined using scanning electron microscopy (SEM). The GC-MS analysis indicated that Thymol (34.08%) was the main oil component, followed by γ-Terpinene (32.99%). The TEM images revealed a spherical-shaped nano droplet with a size of ≤ 100 nm for all nanoformulations. The droplet size and polydispersity index were (445.9 & 0.325), (10.59 & 0.216), and (768.2 & 0.325) for TNE, AgNPs, and TNE-AgNPs, respectively. The calculated LC₅₀ values after 7 days were 11.62, 5.47, 4.08, and 2.38% for TO, TNE, AgNPs, and TNE- AgNPs, respectively. The SEM examination revealed changes in the sensilla base, spiracular plate and anal groove region of the treated ticks. Although the biological parameters of the engorged females did not differ significantly between the treatment and control groups, there was a decrease in the hatchability percent of TO (67%), TNE (65%), and TNE-AgNPs (71%) compared to the control (80%). The used materials demonstrated acaricidal activity and might be candidates for managing the dog tick, R. sanguineus. Further detailed studies are needed to enable good judgment of the use of these materials to control R. sanguineus tick.