Assessment of the acaricidal activity of carvacrol, (E)-cinnamaldehyde, trans-anethole, and linalool on larvae of Rhipicephalus microplus and Dermacentor nitens (Acari: Ixodidae)

The acaricidal activity of carvacrol, (E)-cinnamaldehyde, trans-anethole, and linalool was studied on Rhipicephalus microplus and Dermacentor nitens larvae. All the substances were tested at concentrations of 2.5, 5.0, 10.0, 15.0, and 20.0 mu l/ml, with 10 repetitions per treatment. The modified larval packet technique was employed in the tests and the mortality was evaluated after 24 h. In the groups treated with carvacrol, the lowest concentration (2.5 mu l/ml) was sufficient to cause 100 % death of the R. microplus and D. nitens larvae. The same concentration of (E)-cinnamaldehyde resulted in death of approximately 99 % of the larvae of both tick species and reached 100 % at the other concentrations. For trans-anethole, mortality rates above 90 % of the R. microplus and D. nitens larvae were only observed starting at the concentration of 15.0 mu l/ml and reached 100 % at the highest concentration (20.0 mu l/ml). Finally, the mortality rates of the groups treated with linalool were low, only reaching 8.4 and 14.5 % at the highest concentration (20.0 mu l/ml) for larvae of D. nitens and R. microplus, respectively. These results show that carvacrol, (E)-cinnamaldehyde, and trans-anethole have acaricidal activity, particularly carvacrol and (E)-cinnamaldehyde, both of which resulted in high mortality rates for the larvae of these two tick species even at the lowest concentration.