Acaricidal and synergistic activity of essential oils, their binary combinations, and nanoemulsions against larvae and unfed adult stages of brown dog tick Rhipicephalus sanguineus (Acari: Ixodidae).

Abstract

The growing resistance of ticks to acaricides has made tick management a global concern. Various studies now focus on identifying natural products with acaricidal properties that are environmentally safe. The current research investigates the effect of clove (), mint (), and geranium () essential oils (EOs), along with their combinations and nanoemulsion forms (NE), against() larvae and unfed adults. The chemical composition analysis using Gas chromatography-mass spectrometry (GC-MS) identified eugenol (68.02%) and caryophyllene (20.19%) in clove EO, pulegone (33.48%) and l-menthone (22.28%), in mint EO, and citronellol (22.24%), γ-Eudesmol (13.2%), and Geraniol (10.35%) in geranium EO as the main active constituents. Nanoemulsions were characterized using Transmission electron microscopy (TEM) and dynamic light scattering (DLS) to assure the mean particle size and the mean particle distribution. The reported particle sizes show noticeable differences (e.g., TEM ranges from 47.8 to 173 nm vs. DLS ranges from 80 to 244.2 nm), and the PDI values are relatively high (e.g., 0.55 for geranium NE). According to LCvalues, the most effective materials against larvae were mint NE (LC = 0.36%), followed by the (clove + mint) EO combination (LC = 1.43%), and then clove EO (LC = 1.68%). While the most effective materials against unfed adults were clove NE (LC = 1.63%), followed by (mint + geranium) combination (LC = 4.93%), and then geranium EO (6.1%). The EOs combinations exhibited synergistic efficacy against larvae and unfed adults, with the synergistic factor (SF) > 1. The (clove + mint) binary combination showed a strong synergistic effect against larvae, with SF of 2.46. Furthermore, the (mint + geranium) binary combination exhibited the highest synergistic activity against unfed adults with SF (1.39). These findings suggest that EOs, especially in NE form, represent promising alternatives to chemical acaricides. Future work will focus on studying the possibility of combining NE and evaluating its effect against ticks. More importantly, performing safety evaluation and in vivo study of these formulations to develop efficient and environmentally friendly tick-control materials.