This is a group that seems almost certain to be more complicated and speciose than is currently understood. Blackman and Eastop note that there are two species that are likely not truly congeneric. I agree that C. maxsoni and C. incognita are likely not closely related, but I think there are at least two species lumped within C. incognita. In fact, following my winter 2018 collection curation work, I am now hypothesizing 2-4 species currently confused under the name C. incognita. All of them are found on the foliage of Symphoricarpos in the spring, living among slightly curled leaves, and tended by ants. I am working hard this season to re-collect as many of these as possible on Symphoricarpos that are identified to species — it is possible that each of the four species actually specializes on one species of Symphoricarpos. For a few years I’ve known that the C. ‘incognita’ aphids are heteroecious, migrating to unknown summer hosts. However, in digging through original literature and subsequent synonymies, I found that the secondary host is in fact known — at least one species of Castilleja, living on the crowns of the plants (according to Hottes 1933). Too bad I had not dug hard enough to figure this out sooner. But, it gives me hope to resolve my work on this genus in the coming few years. Only thing is, now I might have to learn the taxonomy of Castilleja, a non-trivial undertaking.
The fundatrices of the Cedoaphis species on Symphoricarpos are highly specialized and have been confused with Aphthargelia in the past, probably due to uncertainty as to what each genus would look like in the fundatrix stage. Further, the dogma put forward in Palmer (1952) and elsewhere that the fundatrix lives on the roots in C. ‘incognita’ is obviously not the case for the Cedoaphis I get on Symphoricarpos.