Inhibitory effects of terpenes on Sarcoptes scabiei in the molting stage

Sarcoptes scabiei is a permanent ectoparasite causing scabies in humans and sarcoptic mange in animals, resulting in significant health and economic impacts worldwide. Current treatments exhibit limited efficacy against eggs and molting mites, leading to treatment failures. Terpenes from essential oils, including carvacrol, eugenol, and geraniol, have previously shown notable acaricidal and ovicidal activity. In this study, molting Sarcoptes mites were exposed to 0.3% carvacrol, 0.9% eugenol, and 1.1% geraniol for 1 h, resulting in molt rates of 74%, 86%, and 88%, respectively, with carvacrol demonstrating superior efficacy (P < 0.001 vs. control). Further investigation revealed that exposure to 1% carvacrol over varying durations (1 ~ 5 h) achieved complete suppression of molting after 4 h, with a LT50 of 1.4 ± 0.4 h, which is significantly higher than active adult mites(LT50 of 3.45 min in prior research). Microscopic analysis demonstrated intra-corporeal droplets were observed within treated molting mites, which suggest that terpenes likely exert their effects by penetrating the cuticle of molting mites, and carvacrol exhibited greater cuticular penetration efficiency. This study provides foundational evidence for the therapeutic use of carvacrol in managing S. scabiei infestations and highlights the need for further research into its mechanisms of action and safety in veterinary and human applications.