Determination of the susceptibility of unengorged larvae and engorged females of Rhipicephalus microplus (Acari: Ixodidae) to different methods of dissolving thymol

Abstract

The present study evaluated efficacy of thymol against engorged females and unengorged larvae of Rhipicephalus microplus when diluted in 1 % dimethyl sulfoxide (DMSO) (formulation 1) and diluted in hydro-ethanol solutions of 50 % (formulation 2), 40 % (formulation 3), and 30 % (formulation 4). The immersion test was used on the engorged females for all dilution methods, while the larval packet method was applied to the larvae to test formulations 3 and 4 since the other two had already been tested before. Two control groups were established in both experiments; in one, ticks were treated with 1 % DMSO, and in the other, with 50 % ethanol, with ten repetitions for each treatment. The groups were maintained at 27±1 °C and RH>80 ± 10 %. For engorged females, the parameters weight before oviposition, egg mass weight, hatching percentage of larvae, and percentage of control were evaluated, while for larvae, percentage of mortality was evaluated. The egg mass weight of all treatments differed significantly (p<0.05) from the control groups; however, the reduction in egg mass weight was more accentuated (p<0.05) in the treatments with formulations 1, 3, and 4. The values of hatching percentage of the group treated with formulation 2 and control group were statistically similar (p>0.05). The group treated with formulation 2 attained the lowest percentage of control (66 %). In the other treatments, the control percentages were greater than 99 %. In larval test, the mortality was 100 % in all the treatments, and there was no mortality in the control groups.