Spectroscopic evaluation of thymol dissolved by different methods and influence on acaricidal activity against larvae of Rhipicephalus microplus (Acari: Ixodidae).
The acaricidal activity of three thymol formulations was investigated at five concentrations (1.25, 2.5, 5.0, 7.5, and 10.0 mg/ml) on Rhipicephalus microplus larvae, and the behavior of its solubility in these formulations was analyzed. The thymol was dissolved in distilled water plus 1 % dimethylsulfoxide as adjuvant under two heating regimes (water bath in formulation 1 and hot plate in formulation 2) as well as without heating in 50 % ethanol and 50 % water (v/v). The acaricidal activity was assessed by the modified larval packet test, and the solubilization behavior was investigated by ultraviolet-visible spectroscopy, based on the Beer-Lambert law. With formulations 1 and 2, the mortality was greater than 95 % starting at the thymol concentrations of 5.0 and 7.5 mg/ml, respectively, while with formulation 3, this mortality level was reached starting at a concentration of 2.5 mg/ml, showing that the addition of ethanol in the solution enhanced the acaricidal action of thymol. This result was supported by the LC 90 values, which were 3.3, 2.4, and 1.6 mg/ml of thymol for formulations 1, 2, and 3, respectively. This result is related to the better solubility of thymol in the hydroethanolic formulation, since the spectroscopic analysis revealed that the thymol dissolved more completely in this formulation. This fact was evident once the R (2) obtained from the linear regression analysis of the relation absorbance × concentration of the formulations 1, 2, and 3 approached the optimal value (R (2) = 1) in the following sequence: 1, 2, and 3 (0.717, 0.901, and 0.968, respectively).
Programa de Pós-graduação em Comportamento e Biologia Animal, Universidade Federal de Juiz de Fora, Rua José Lourenço Kelmer, s/n-Campus Universitário Bairro Martelos, 36036-330 Juiz de Fora, MG, Brazil.
Erik
E
Daemon
Caio Márcio Oliveira
CM
Monteiro
Ralph
R
Maturano
Tatiane Oliveira Souza
TO
Senra
Fernanda
F
Calmon
Aline
A
Faza
Márcia Cristina
MC
de Azevedo Prata
Stéfanos Leite
SL
Georgopoulos
Luiz Fernando Cappa
LF
de Oliveira
D056810:Acaricides / Q000737:chemistry / Q000494:pharmacology*; D000818:Animals; D005260:Female; D007814:Larva / Q000187:drug effects; D048494:Rhipicephalus / Q000187:drug effects* / Q000254:growth & development; D012995:Solubility; D013057:Spectrum Analysis; D013943:Thymol / Q000737:chemistry / Q000494:pharmacology*
D056810:Acaricides; D013943:Thymol