This is one of the groups I study extensively in the field, and puzzle over in the lab. It is almost entirely North American and is likely very closely related to Macrosiphum; in fact the two genera might be better thought of as a mish-mash of similar species haphazardly assigned to genera based on a possibly trivial character, i.e. clavate siphunculi. But as you’ll see from careful study, some species placed in Macrosiphum have clavate siphunculi as well. So what gives? Hard to say. Probably extensive field work and fresh collections for DNA analysis would be required to clarify the genus-level classification. Meanwhile, there are many cool and easily recognized species of Illinoia to enjoy in the field.
Illinoia corylina (Davidson)
I have pursued this aphid for over 2 decades, and only collected it several times on Corylus. I have a fundatrix, some apterae and some alatae from Corylus that I identify as this species.
That said, there is some concern that what I see developing on Corylus in the spring may actually be a different species, such as I. macgillivrayae (see below). I agree that some of my specimens may have fewer setae on the ultimate rostral segment than is expected in I. corylina, and that the situation of native Illinoia on shrubs in western North America is unclear. Nonetheless, I file a range of things under this species, including many Illinoia collected on Aquilegia (columbine) in natural systems. The latter host association was suggested by other specialists many years ago, and I suspect they were correct. This species will continue to be a subject of my study for years to come. I have this ‘species’ from Washington, Oregon, and California.
Illinoia (Amphorinophora) crystleae (Smith & Knowlton)
I have a lot of affection for this species, and have pursued it avidly in the field for 20 years. It lives on one of our native honeysuckles, Lonicera involucrata (a host whose berries were described as inedible and possibly poisonous, “but they are so disgusting that there is little chance of anyone eating enough to worry.” Plants of the Rocky Mountain Region). My gut feeling (forgive the pun) is that this species belongs to a Caprifoliaceae-associated lineage that includes Macrosiphum stanleyi, Macrosiphum raysmithi, Macrosiphum diervillae, Macrosiphum schimmelum, and a few others. This is another research topic I invite others to pursue. It’s a very interesting biogeographical puzzle. I so far have this species from the ocean to rather high mountains; states/provinces include: British Columbia, Washington, Oregon, Idaho, and Colorado.
Illinoia goldamaryae (Knowlton)
This is one of apparently two common Illinoia sensu stricto species that live on Asteraceae (the other being I. grindeliae). I have collected it on several different hosts, but the place I was most able to study it and collect all its life cycle stages was on Solidago on the shores of Moses Lake in central Washington. I have fundatrices, oviparae, and alate males from Solidago. My specimens are from: Washington, Oregon, Idaho, Montana, and Wyoming.
Illinoia (Oestlundia) maxima (Mason)
This is a beautiful aphid that can be found on Rubus parviflorus (thimbleberry) in the moist parts of northwestern North America. As noted by Blackman and Eastop, it has an abbreviated life cycle and is monoecious on this shrub. I have samples from British Columbia, Washington, and Oregon.
Illinoia (Masonaphis) menziesiae Robinson
This is an interesting species that is an example of an ‘Illinoia‘ with little to no swelling in the siphunculi. It is also unusual in that it causes discoloration of the leaves on which it feeds (host being Menziesia ferruginea, Ericaceae). Once I learnt to recognize Menziesia from among all the other nondescript shrubs in northern Idaho, this aphid was easy to find. Another interesting tidbit is that the specimens collected on Menziesia near the ocean coast in Oregon’s Tillamook County differ rather markedly in morphology from specimens collected east of the Cascade Range in Washington, Idaho, and Montana; the leaf discoloration symptom of infestation was the same. More study might determine that two species are involved.
Illinoia richardsi (MacGillivray)
This aphid is common and easy to find on its host Anaphalis margaritacea (Asteraceae). It has an impressively large, apparently natural distribution that reflects the distribution of its hosts across North America. I have specimens from Washington, Oregon, Idaho, Utah, and Quebec.
In my collection I group specimens together that might be identified as either I. macgillivrayae or I. spiraeae (in fact, several of the species known from Ericaceae are also very difficult to recognize when looking at the full range of material at hand). The reason for this is that, although I get the general trend in size of ultimate rostral segment and cauda that is used to separate these species, their distribution and broad host range almost completely overlap. This means separating the species is troublesome at best, and may be misguided if all these specimens in fact represent only one species. Illinoia in this general group are common in the mountains in Washington, Oregon, and Idaho. Alates can be abundant and found colonizing a wide range of plants on which they may or may not be able to complete development. The latter fact makes it hard to know the full host range of these Illinoia aphids, but here is a start on the list:
Asteraceae: Hieracium, Senecio
Ericaceae: Arctostaphylos, Phyllodoce, Rhododendron, Vaccinium
Ranunculaceae: Aquilegia, Thalictrum
Rosaceae: Amelanchier, Crataegus, Geum, Holodiscus (there is at least one other distinct and apparently undescribed Illinoia on Holodiscus), Prunus, Sorbus, Spiraea