Acaricidal activity of the essential oil from Tetradenia riparia (Lamiaceae) on the cattle tick Rhipicephalus (Boophilus) microplus (Acari; Ixodidae)

Tetradenia riparia (Lamiaceae) is a well-known herbal medicine with a variety of useful properties, including its acaricidal effect. This experiment was carried out to study the bioacaricidal activity of T. riparia essential oil (EO) against engorged females of Rhipicephalus (Boophilus) microplus (Acari; Ixodidae). For this purpose, nine serial concentrations (12.50%, 6.25%, 3.75%, 1.80%, 0.90%, 0.45%, 0.22%, 0.11%, and 0.056% w/v) of T. riparia were used for the adult immersion test (AIT). For the larval packet test (LPT), we used 14 serial concentrations (100.00%, 50.00%, 25.00%, 12.50%, 6.25%, 3.65%, 1.82%, 0.91%, 0.45%, 0.228%, 0.114%, 0.057%, 0.028%, and 0.014% w/v). The results for AIT showed 100.00% and 2.05% mortality, 19.00 and 90.20% for the total number of eggs, egg-laying inhibition of 0.00% and 90.20%, hatchability inhibition of 0.00% and 70.23%, and product effectiveness of 100.00% and 2.89%, respectively. The AIT indicated that the LC50 and LC99.9, calculated using the Probit test, were for mortality (%) 0.534 g/mL (0.436-0.632) and 1.552 g/mL (1.183-1.92); for total number of eggs were 0.449 g/mL (0.339-0.558) and 1.76 g/mL (1.27-2.248); and for hatchability inhibition were 0.114 g/mL (0.0-0.31) and 2.462 g/mL (1.501-3.422), respectively. Larvae between 14 and 21 days old were fasted and placed in each envelope. Bioassays were performed at 27 degrees +/- 1 degrees C, RH >= 80%. Larval mortality was observed 24 h after treatment and showed 10.60-100% mortality in the LPT bioassay. The LPT showed that the LC50 and LC99.9 were 1.222 g/mL (0.655-1.788) and 11.382 g/mL (7.84-14.91), respectively. A positive correlation between T. riparia EO concentration and tick control, was observed by the strong acaricidal effects against R. (B.) microplus, and the mortality rate of ticks was dose-dependent. Our results showed that T. riparia is a promising candidate as an acaricide against resistant strains of R. (B.) microplus. Crown Copyright (C) 2011 Published by Elsevier Inc. All rights reserved.