Bucculatrix mirnae Vargas and Moreira, 2012 (Lepidoptera, Bucculatricidae) is a micromoth native to the coastal valleys of the Atacama Desert previously known to occur only in the type locality of the Azapa Valley, close to sea level. Its immature stages are associated with the shrub Baccharis salicifolia (Ruiz & Pav.) Pers. (Asteraceae). We report data on the occurrence of B. mirnae found for the first time at 3500 m above sea level on the western slopes of the Andes mountains of northern Chile. In addition, Baccharis alnifolia Meyen & Walp. is recorded as a new host plant for B. mirnae. The implications of this finding for conservation in the arid western slopes of the Andes habitats in northern Chile are discussed.