In the southern region of Rio Grande do Sul State, European cattle represent the most important stock used for meat and milk production. This region is considered a marginal area for the occurrence of the tick Boophilus microplus, which parasites the cattle between the end of September and early May. The damage caused by this parasite is high, which has been aggravated by the selection of tick populations resistant to acaricids. The aim of this present research was to evaluate the sensibility/resistance situation of Boophilus microplus, as well as the dynamic of the use of different acaricids in the last decade. During the period of study, tick samples from 124 farms, collected in 14 counties of the region, were analyzed. In each farm engorged female ticks and information about the acaricids management were collected. In order to test the sensibility/resistance we used the immersion test of the engorged females tick performed at the Laboratório de Parasitologia do Instituto de Biologia da UFPel . We observed that in the first three years of the last decade a selection of resistant tick populations was induced by pyretroids products. Products that used amitraz as a main compound, the most important acaricids used in the last three years of the decade, also induced resistant selection in the tick population to this drug. In the first three years of the studied period all tick populations analyzed where sensitive to amitraz (efficacy index = 95%). However, in the last three years of the decade, the efficacy index detected drop to 79% in the studied populations. Managing inaccuracy in the region where detected such as, number of application higher than six times a year, application of acaricids only when the adults forms where visualized and the exclusive use of the acaricid for the tick control, that might predispose to the selection of resistant populations.
tick control; acaricides; Boophilus microplus; bovine
