Atividade carrapaticida do timol sobre larvas e ninfas de Amblyomma cajennense (Acari, Ixodidae) fêmeas ingurgitadas e ovos de Rhipicephalus (Boophilus) microplus (Acari, Ixodidae)

Abstract

Among the various species of Ixodidae existing in the Neotropics, Rhipicephalus (Boophilus) microplus and Amblyomma cajennense are two of the ones that arouse more economic and public health interest, causing losses in animal production and acting as pathogens vectors. The use of synthetic chemical acaricide is the predominant method in controlling these arthropods; however, the indiscriminate use has resulted in serious problems such as the pressure on the selection for resistant ticks and the risk of animal and man toxicity. An alternative to this method has been the use of plant origin substances with little or no toxicity to animals and humans. The fore, this study aimed to evaluate the acaricide activity of thymol in different concentrations on larvae and nymphs of A. cajennense and engorged females and eggs of R. microplus. The study was conducted in the Advanced Laboratory of Zoology at the Federal University of Juiz de Fora, Minas Gerais, Brazil. In the first study (divided into two experiments) it was evaluated the influence of different concentrations of thymol (1.0%, 1.5% and 2.0%) on the biological parameters of the non-parasitic phase of R. microplus engorged females and also its activity on the eggs of this tick. The following biological parameters were observed: initial weight (mg), eggs weight mass (mg), pre-oviposition (days), oviposition period (days), survival period (days), percentage of hatching; egg production index (IPO), nutritional index (NI) and treatment efficacy. In the first experiment, the parameters weight of the female before oviposition and pre-oviposition presented no significant differences (p> 0.05) between groups. The different concentrations of Thymol caused changes in the parameters eggs weight mass, oviposition period, survival period, percentage of hatching, IPO, and IN, having found highly significant differences between the treated and control groups (p <0.01) . Control efficacy was greater than 95% in all treatments, reaching 99% at 2.0%. The percentage of hatching was not affected in any treatment (p> 0.05). In the second study it was evaluated the acaricide potential of Thymol on not engorged and engorged larvae and engorged nymphs of A. cajennense. The values concerning the mortality of not engorged larvae were 18.2%, 51.8%, 97.6%, 93.5%, 94.5%, and for engorged nymphs they were 26.0%, 92.2 % 100.0% 100.0% 100.0% at concentrations of 0.25%, 0.5%, 1.0%, 1.5% and 2.0% respectively. In tests with engorged larvae the mortality was 100.0% in all treatments. The results found in this study demonstrate that Thymol has an acaricide action, interfering in the majority of the analyzed parameters for R. microplus, also showing acaricidal activity on immature A. cajennense, being larvae and engorged nymphs more susceptible than not engorged ones.