Pinus nigra (black pine) is a Mediterranean taxonomic complex (including different subspecies), with a discontinuous distribution. The southernmost part of its range is in North Africa, in Morocco and Algeria, where it is present as P. nigra subsp. mauretanica. Currently, an extremely limited number of trees of this subspecies still persist within its natural range, giving this taxon an outstanding ecological importance. These residual stands are threatened by many biotic and abiotic factors, putting at risk the survival of this subspecies in its natural habitat. This paper reports for the first time the presence of Eulachnus tuberculostemmatus (Hemiptera: Aphididae: Lachninae) in Algeria, and its infestation on P. nigra subsp. mauretanica. This insect was detected in three sites of the Djurdjura National Park in May 2012 and identified in February 2016. The aphid seems to be responsible for needle discoloration and premature senescence, symptoms observed since spring 2008 on the infested pines. These clusters of P. nigra subsp. mauretanica trees are protected by park regulations, and given their conservation status further investigations into this pest species, and other biotic and abiotic factors that may threaten this important tree, are required.