In vitro toxicity of cypermethrin and deltamethrin on the cattle tick Rhipicephalus microplus / Toxicidade in vitro da cipermetrina e deltametrina sobre o carrapato-do-boi, Rhipicephalus microplus

ABSTRACT

The objective of this work was to evaluate the efficacy of cypermethrin 15% and deltamethrin 25% of the cattle tick Rhipicephalus microplus, using immersion test of engorged females (ITEF) and impregnated Pasteur pipette (PIPT). The following dilutions were used T1 =1/1000 mL (v/v), T2 = 2/1000 mL, T3 = 4/1000 mL and T4 = 8/1000 mL, respecting the dosages prescribed by the manufacturers for both pyrethroids. The Experiment I used adult females, and the acaricidal efficacy was tested on engorged females, that were collected separately from ten dairy herds in the Descalvado region, SP. The data revealed that the efficacy for cypermethrin ranged from 0.0 to 95.9% and for deltamethrin was 34.4% to 99.2%. We have observed that the efficacy of deltamethrin and cypermethrin was higher than 95%, in only four farms. Treatment with cypermethrin at 8/1000 mL dilution resulted in 100% of efficacy against larvae after 120 minutes. Deltamethrin at 8/1000 mL dilution resulted in 100% of larvae exhibiting paralysis after 60 minutes. The data revealed that the efficacy for cypermethrin ranged from 0.0% to 95.9% and for deltamethrin was 34.4% to 99.2%. We have observed that the efficacy of deltamethrin and cypermethrin was higher than 95%, in only four farms. The experiment II used the PIPT against larvae and the efficacy of the same products was checked at 5, 10, 20, 30, 60, 120, 360 and 720 min post-treatment. Treatment with cypermethrin at 8/1000 mL dilution, resulted in 100% efficacy against larvae after 60 min and 100% of larvae treated with deltamethrin presented paralysis 30 min post-treatment with the dilution of 8/1000 mL. Although both pyrethroids were 100% efficacious against larvae, the low percentage of adulticidal efficacy confirms the existence of resistant strains of this tick species.[...]

RESUMO

O objetivo deste trabalho foi avaliar a eficácia de cipermetrina 15% e de deltametrina 25%, contra cepas do carrapato-do-boi Rhipicephalus microplus, utilizando as técnicas de imersão de fêmeas ingurgitadas (TIFI) e da pipeta Pasteur impregnada (TPPI). Respeitando-se as dosagens prescritas pelos fabricantes para ambos os fármacos, foram utilizadas as seguintes diluições T1 1/1000 mL (v/v), T2= 2/1000 mL, T3 = 4/1000 mL, T4 = 8/1000 mL. No experimento I, o TIFI foi utilizado em fêmeas adultas ingurgitadas, colhidas separadamente em dez propriedades na bacia leiteira da região de Descalvado, SP. Os resultados revelaram que eficácia da cipermetrina variou entre 0,0% e 95,9% e para a deltametrina foi de 34,4% a 99,2%. Observou-se que a eficácia >95% da deltametrina e cipermetrina sobre o carrapato, ocorreu em apenas quatro propriedades. No experimento II, com larvas, o TPPI foi utilizado para determinar a eficácia larvicida dos mesmos produtos por meio da perda de motilidade das larvas, nos tempos 5, 10, 20, 30, 60, 120, 360 e 720 minutos pós-tratamento. O tratamento com cipermetrina na diluição de 8/1000 mL resultou em 100% de eficácia contra larvas após 120 minutos. A deltametrina causou paralisia de 100% das larvas após 60 minutos na diluição de 8/1000 mL. Apesar de ambos os piretróides apresentarem 100% de eficácia contra larvas, o baixo percentual de eficácia adulticida comprovou a existência de cepas resistentes destes ácaros. [...]