Natural bioactive compounds as an alternative to control ectoparasites of veterinary importance

Introduction: To date, the use of synthetic pesticides is the most common method for control of ectoparasites in veterinary medicine. However, the indiscriminate overuse of synthetic pesticides has ledto concerns related to environmental pollution and development of resistance in pest populations. In this scenario, eco-friendly and cost-effective tools to protect animals from ectoparasites would be welcome and attractive to global market. Several plant extracts and essential oils have already been identified as being toxic to ectoparasites. Notably, despite many researches on botanical acaricides, these preparations had poor market penetrations, mostly due to their poor stability and wide variations in the chemical composition according to the time or geographical area of collection. To face these issues, the isolation of pure bioactive components from the plants and their evaluation as pesticides is recommended. Monoterpenoids are important chemical constituents of plant essential oils and seem to possess promising effects against a number of arthropod pests of veterinary significance. Material and Methods: Acaricidal activity of two monoterpenoids, carvacrol and thymol, against the poultry red mite, Dermanyssus gallinae, was assessed by contact and fumigant toxicity bioassays. For residual toxicity assay, mortality rate of mites recorded after being exposed to the surfaces 7, 14, 21, and 28 days post spraying. We also evaluated the ovicidal, larvicidal and repellency effects of these compounds against castor bean tick, Ixodes ricinus. Results: Carvacrol and thymol demonstrated good efficacy and high toxicity on D. gallinae, in vitro and in field conditions as well. Combination of carvacrol and thymol led to synergistic acaricidal activity and prolonged toxicity. Furthermore, we showed that carvacrol and thymol tested at low concentrations led to a significant hatching decrease in eggs of I. ricinus, showing an efficacy higher than permethrin. In the treatment of larvae of I. ricinus with carvacrol and thymol, mortality rates reached 100% after 24 h. These compounds also at all concentrations tested showed > 90% repellency on I. ricinus. Conclusion: The results of our research, along with the low toxicity of the tested products for human and environment, and low residue level in animal products, highlighted the promising potential of the above mentioned monoterpenoids, to develop newer and safer control tools against ectoparasites of veterinary importance.