This is a easily recognized genus for a small but unknown number of species. As noted by Blackman and Eastop, “most species are poorly known.”
Another case of understatement. In my collection I somewhat confidently identify two species, and all the others I have turned to separation based on “morphospecies” without assigning published names. Without extensive further work, this is one of those genera where writing a species name on a slide is little more than misleading. I have been avidly collecting Nearctaphis for over 20 years, and will continue to do so. Perhaps if I live another 30 years, there will be enough material to revise the genus (maybe sooner for someone smarter than me).
Nearctaphis bakeri (Cowen)
This is a very common species that has become a pest of cultivated Trifolium. I collect it frequently on its Rosaceae primary hosts, especially on ornamental Pyrus and various Crataegus. On secondary hosts, I find it on a range of Trifolium (Fabaceae) species and Penstemon (Plantaginaceae). It is widespread in North America, and I have material identified as this species from Washington, Oregon, Idaho, Wyoming, Wisconsin, and New York.
Nearctaphis (Amelanchieria) sensoriata (Gillette & Bragg)
This is the Nearctaphis that I find most commonly, probably because it is abundant and very apparent on its Amelanchier (Rosaceae) hosts in the spring and fall. As noted by others, it is probably heteroeceous, but I have yet to find a secondary host for it. Most likely such a host would be Fabaceae, and probably the roots or underground stems. I am not as adept at collecting underground aphids as I could be…. I have material from Washington, Oregon, Idaho, Montana, California, Nevada, Colorado, and New Mexico.