The three species of Hyalopterus Koch cause economic damage to various stone fruit trees of the genus Prunus L., H. pruni (Geoffroy), H. amygdali (Blanchard), and H. persikonus Miller et al. Although the third species was established recently, it has been suggested that one of the twelve older synonyms of the first two may be applicable to the third. We undertook a synonymic revision of the nominal species of Hyalopterus to clarify the taxonomy and nomenclature of the genus. The three valid species of Hyalopterus are affirmed to be H. pruni (the mealy plum aphid), H. amygdali, and H. arundiniformis Ghulamullah, stat. nov. We determined that H. mimulus Börner and H. persikonus are junior synonyms of H. arundiniformis, syn. nov., and that Brachysiphum kobachidzei Rusanova is not a synonym of H. amygdali but a valid species of Aphis, stat. nov., comb. nov. Aphis amygdalipersicae Mosley is likely a senior synonym of Brachycaudus helichrysi (Kaltenbach), syn. nov.; to maintain current usage, we establish the former as a nomen oblitum with respect to the latter. Finally, several other nominal species were unevaluable and are therefore listed as nomina dubia.