In vitro anti-tick effect of Eucalyptus globulus oil and its nano-emulsion against unfed adults of the brown dog tick Rhipicephalus sanguineus sensu lato (Acari: Ixodidae).

Rhipicephalus sanguineus Latreille (Ixodida: Ixodidae) has an economic impact as it is a blood-feeding ectoparasite transmitting numerous pathogens to humans and animals. The present study evaluated the acaricidal effect of eucalyptus essential oil (EO) with the concentrations (40%, 30%, 20%, 10%, 5% and 2.5%), eucalyptus nano-emulsion (ENE) with the concentrations (30%, 20%, 15%, 10%, 5%, and 2.5%), ENE combined with silver nanoparticles (ENE & SNPs) with the concentrations (5%, 4%, 3%, 2% and 1%) and SNPs with the concentrations (5%, 4%, 3%, 2% and 1%) on unfed adults of R. sanguineus sensu lato using the adult immersion test. There were two controls, one with tween 80 and the other without tween 80, while Bravecto® was used as an acaricidal reference. The nanoformulations were analysed by particle size, UV-visible spectroscopy, and transmission electron microscopy (TEM). The mortality of treated R. sanguineus was recorded daily for 7 days. The mortality of ENE and SNPs, EO and SNPs at 7 days was 96.6%, 90% and 80%, at concentrations of 5%, 40% and 5%, respectively. The lethal concentration to 50% mortality (LC50) of EO, ENE, ENE and SNPs, and SNPs at 7 days was 6.65, 9.49, 2.23 and 4.08%, respectively. The particle size of nanoformulations was (83.08, 10.59 and 223.4 nm) for ENE, a mixture of SNPs, and ENE and SNPs, respectively. Scanning electron microscopy of treated adult R. sanguineus revealed numerous alterations in aeropyles of spiracular plates, anal grooves and mouthparts. The histopathological examination of the treated adult R. sanguineus showed degeneration in the cuticle, midgut and salivary gland. These findings demonstrate that eucalyptus oil could be used as part of an integrated pest management program for the control of R. sanguineus.