A new vagrant species of Diptilomiopidae mite, in the Diptacus Keifer, 1951 genus, namely Diptacus rubuscolum sp. nov., living on the lower leaf surface of blackberry-Rubus sp. (Rosaceae) in South Brazil, is described and illustrated. In addition, Acalitus orthomerus Keifer, 1951, for the first time reported in Brazil and even in South America; a supplementary description of this species is presented based on females, males and immature specimens associated to the drupelets. Main morphological differences distinguishing the new Diptacus species and A. orthomerus species from those belonging to the same genera or morphologically similar also associated with Rubus are presented.