RESUMO

The ixodicidal activity of the methanolic extracts of Artemisia ludoviciana (Astereceae), Cordia boissieri (Boraginaceae) and Litchi chinensis (Sapindaceae) against two field populations of Rhipicephalus (Boophilus) microplus from the state of Nuevo Leon (NL) and Veracruz (VER) was evaluated. The extract of L. chinensis in the concentration of 150 mg/ml showed efficacies of 100% and 99% against engorged females and mortalities of 98% and 99% against larvae. C. boissieri in the same concentration showed efficacies of 71% and 37% against engorged adults and mortalities of 33.04% and 10.33% against larvae and A. ludoviciana had efficacies of 94% and 83% in adults and mortalities of 89.39% and 89.21% against larvae in both populations respectively. The enzymatic activity of Acetylcholinesterase (AChE), Carboxylesterase (CaE), Glutathione-S-Transferase (GST) and Alkaline Phosphatase (ALP) was measured in both populations of ticks. As a result, a significant difference between both populations was shown, being the VER population the one that exhibited a higher enzymatic activity (p ≤ 0.05). It can be concluded that the methanolic extract of the seed of L. chinensis shows potential ixodicidal activity and can be used as an alternative source of tick control, however, prior characterization, toxicity and formulation studies are necessary.

No presente trabalho, a atividade ixodicida de extratos metanólicos de Artemisia ludoviciana (Astereceae), Cordia boissieri (Boraginaceae) e Litchi chinensis (Sapindaceae) contra Rhipicephalus (Boophilus) microplus foi avaliada em duas populações de campo nos estados de Nuevo León (NL) y Veracruz (VER). O extrato de L. chinensis na concentração de 150 mg/ml, apresentou eficácia de 100% e 99% contra fêmeas ingurgitadas, e taxas de mortalidade de 98% e 99% contra larvas. C. boissieri, na mesma concentração, apresentou eficácia de 71% e 37% contra adultas ingurgitados, e taxas de mortalidade de 33,04% e 10,33% contra larvas e A. ludoviciana apresentou eficácias de 94% e 83% em adultos e mortalidade de 89,39% e 89,21% contra larvas em ambas as populações respectivamente. Por outro lado, a atividade enzimática da Acetilcolinesterase (AChE), Carboxilesterase (CaE), Glutationa-S-Transferase (GST) e Fosfatase Alcalina (ALP) foi medida em ambas as populações de carrapatos. Como resultado, foi apresentada uma diferença significativa entre as populações, sendo a população VER a que apresentou maior atividade enzimática (p ≤ 0,05). Assim, pode-se concluir que o extrato metanólico da semente de L. chinensis apresenta potencial atividade ixodicida e pode ser utilizado como fonte alternativa de controle de carrapatos, porém estudos prévios de caracterização, toxicidade e formulação são necessários.

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RESUMO

Rhipicephalus sanguineus s.l. is an intra- and peridomiciliary tick of medical and veterinary importance, whose control is carried out through the application of various ixodicides, to which it can develop resistance. The objective of this work was to determine the discriminant doses (d.d.) to identify resistance against three ixodicides - fipronil, flumethrin and coumaphos - in R. sanguineus s.l. larvae originating from Mexico. Engorged ticks were collected from naturally infested dogs residing in rural communities in five Mexican states; the dogs had no history of recent treatment with ixodicides. All ticks were identified as R. sanguineus s.l. They were incubated for 25 days and their progeny was used in the larval package test (LPT) to be exposed to d.d. as determined in Rhipicephalus microplus, and those that were susceptible were analyzed using the LPT with six concentrations, for fipronil from 0.1 to 0.003125%, for flumethrin from 0.02 to 0.000625% and for coumaphos from 0.4 to 0.0125%. Mortality was analyzed with Probit methodology, to calculate the 50 and 99% lethal concentrations (LC50 and LC99). The d.d. was determined as a consensus value by multiplying the LC99 value × 2. Nine double susceptible samples (fipronil + flumethrin) and one triple susceptible sample (fipronil + flumethrin + coumaphos) were found; the d.d. determined were fipronil 0.05%, flumethrin 0.01% and coumaphos 0.43%. These doses can be used to rapidly and inexpensively identify resistant populations in samples collected in the field.

RESUMO

The effects of six new synthetic carbamates on fully engorged females of four Rhipicephalus microplus strains (one reference strain susceptible to conventional ixodicides, two strains multiresistant to ixodicides and one tick field isolate) were compared. In addition, the effect of two other new synthetic carbamates was tested on larvae from the same strains. The first six tested carbamates reduced egg laying and inhibited egg hatching in the four studied strains (P<0.05). Compared with untreated females, the eggs produced by the treated engorged female ticks of all strains had a dark, dry, opaque appearance and were less adherent. The remaining two tested carbamates induced larval mortality in all of the evaluated strains. The three studied R. microplus strains displayed 50% resistance ratios (RR50) of less than 2 when compared to the susceptible reference strain. These results demonstrate that both carbamates with a larvicidal effect and carbamates that inhibit egg laying and embryo development are efficacious against tick strains that are resistant to commercial ixodicides, no cross resistance was observed.

Assuntos