The fourteen aphid species recorded as feeding on Holodiscus (Rosaceae) are listed, discussed, and a key to species provided. One new species is described, Acyrthosiphon rockspirea new species, which lives throughout the year on Holodiscus in a wide range of habitats. Two names, Aphis coweni Palmer and Aphis holodisci Robinson are declared to be new junior synonyms of Aphis cercocarpi Gillette and Palmer and much taxonomic data and information are provided to support these conclusions. The heteroecious life cycle of A. cercocarpi between Holodiscus and Veratrum (Melanthiaceae) is described, and biological and taxonomic information, and a key to aphids known from Veratrum, are provided. The correct host plant, monoecious life cycle, and taxonomic features of Illinoia gracilicornis (MacGillivray) are discussed, including brief descriptions of all morphs. The heteroecious life cycle of Macrosiphum walkeri Robinson is documented for the first time, with brief descriptions of the oviparae and males.