Laboratory and field efficacy of terpene combinations (carvacrol, thymol and menthol) against the poultry red mite (Dermanyssus gallinae)

Abstract

In this study, we evaluated the efficacy of combinations of the terpenes carvacrol, thymol, and menthol on Dermanyssus gallinae under in vitro (direct contact and vapour efficacy assays) and in-use conditions. Combinations investigated in vitro included carvacrol-menthol, thymol-menthol, carvacrol-thymol, and carvacrol-thymol-menthol. Results from contact efficacy studies showed that carvacrol-thymol-menthol was the most efficacious compared to the other combinations (P < 0.05), killing 100 % of the mites when at a concentration of 0.5 μg/mL. Thymol-menthol showed the weakest acaricidal activity with an approximate 80 % mortality rate at a concentration of 2 μg/mL. Based on the results of the vapour efficacy assay, all tested combinations appear to exert their acaricidal efficacy not only through direct contact, but also by fumigant action. A subsequent in-field efficacy investigation in a cage system laying farm was carried out to confirm the miticidal activity of the carvacrol-thymol-menthol combination. A formulation based on the triple combination of carvacrol-thymol-menthol diluted 1:40 in water was sprayed, with 1-week interval, in an 8000-laying hen farm, in presence of hens. The number of mites were counted by monitoring traps for 21 days through the study. The number of mites in the treated group decreased until day 5 after the first spray, but increased on days 5 and 7. However, after the second spray on day 7, the number of mites showed a significant decrease on day 10. This terpene-based combination which showed promising in vitro and in field miticidal activity can be a step forward in greening the future of pest management, also producing residue-free eggs.