This is the most speciose genus of aphids, with over 500. That is about 10% of all aphid species. It seems to me to speciate readily in association with host plant species or genera. My feeling is that there are many species yet to be discovered and/or described, but also that there are many synonymies yet to be discovered and documented. Some of the latter will undoubtedly be host-alternation biologies that have yet to be elucidated. I will probably dare to describe a couple species of Aphis soon; they are pictured below.
Aphis agastachyos Hille Ris Lambers
Arguably, this species may belong in the subgenus Bursaphis — it looks like a Bursaphis, and shares the unusual feature of several accessory setae on the ultimate rostral segment. But, I follow the current practice and list as Aphis sensu stricto. This species lives on the mint genus Agastache, with an abbreviated life cycle ending in June or July. I have also collected this species, or something very similar, from Monardella odoratissima, another mint species that interestingly smells almost identical to Agastache urticifolia. I have material from Washington, Oregon, and Idaho.
Aphis asclepiadis Fitch (formerly Aphis carduella Walsh (formerly Aphis helianthi Monell))
This is a species that cannot be missed when collecting in the inland Pacific Northwest, especially the mountains connected to the Rockies and the Sierras.
It overwinters on Cornus stolonifera, then migrates to many secondary hosts throughout summer. In the mountains I frequent, this species is analagous to Macrosiphum euphorbiae in that it colonizes many hosts, and a majority of samples of Aphis from high mountain sites and in and near the northern Rocky Mountains seem to be this species. Have a look at my collection database for more details on hosts.
Aphis craccivora Koch
This is a common pest aphid, now distributed throughout most of the world. It is known as a crop pest in many places, particularly the tropics and subtropics, but in the north temperate areas I frequent, it is most common on invasive weeds. If you’ve watched old cowboy movies, you’ve probably seen one of Aphis craccivora‘s most common hosts in our areas: tumble weed (also known as Russian thistle, Kali tragus). Most years in the fall, this aphid’s populations explode on Kali tragus as it matures.
Aphis fabae Scopoli
This aphid, also known as black bean aphid, is one of those pest species that is now distributed nearly worldwide. Although it has “bean” in its name, I very rarely see it on legumes of any kind.
The A. fabae in western North America seem to fit the categories (subspecies) discussed by Blackman and Eastop that colonize Asteraceae and various other plants. That said, I am skeptical that subspecies defined reasonably well through host plant biology and slight morphological differences in Europe will be particularly meaningful in North America. As a consequence, I file everything in the A. fabae group in one box in my collection.
This is an introduced species that has managed to slot into native plant systems in North America, such as commonly overwintering on native Viburnum and Philadelphus species, and turning up (apparently, if my taxonomy is trustworthy) on things like Valeriana and Veratrum in the mountains. However, the most common habitats for it in my area are still cropping systems and landscapes.
Aphis farinosa Gmelin
A very interesting species, A. farinosa occurs across the entire northern hemisphere in temperate areas, feeding without host alternation on many species of Salix (willow) (it also occurs in Argentina, according to Blackman and Eastop). The biogeography of animals like this intrigues me: native or introduced? How long has it been so widely distributed? And so on.
I have some affection for this species because of its audacious-long siphunculi and its colorful colonies full of oviparae and males by early summer.
Aphis gossypii Glover
This is another pest aphid of almost cosmopolitan distribution, for which I have little affection, also known as cotton aphid and melon aphid.
In the northern temperate areas I collect, it is relatively uncommon, thank goodness, being far more common and polyphagous in the subtropics and tropics. As you can read in Blackman and Eastop and elsewhere, this species is terribly variable and complicated taxonomically. Although some want to split it into several species, my relative isolation from major collections and biological study of the species in the field both lead me to lump specimens in my collection.
As you can see from just the photos presented here, A. gossypii varies a lot in color and appearance. I have seen it almost white, and so tiny that adults were far under 1 mm in length. Walk through a place like Orlando, Florida or San Antonio, Texas, and A. gossypii is likely to be the main aphid living on ornamentals, including the smallest herbs to fully expanded leaves of trees. During my postdoc years at the USNM, identification of aphids intercepted at ports of entry was generally a long string of A. gossypii and Myzus persicae, occasionally punctuated with something else.
In our Idaho garden, it seemed to appear only late in the summer and fall, colonizing several different plants, apparently flying in from elsewhere.
Aphis holodisci Robinson
This species is a real puzzle for me, the dogma being that it is monoecious holocyclic, yet I suspect a host alternation of at least some of the Aphis that appear to be this species that live on Holodiscus discolor (ocean spray). One possibility is that there are two or more species being slotted into this name, or, that host alternation is indeed facultative. The latter life cycle trait is not unknown in aphids.
Here is one of those leads somebody can steal and run with if they want to: I wonder whether one of the Aphis that colonizes Veratrum in my area (there are at least 2 species of Aphis on Veratrum) uses Holodiscus as primary host and might be the species called A. holodisci by A.G. Robinson (one of my heroes who I never met in person). I have accumulated a lot of material from both hosts but have not had time to study it all thoroughly. It is obvious from the field that at least one of these Veratrum-feeding Aphis is heteroecious. I am not yet sure about the other.
Aphis lupini Gillette & Palmer
As noted by Blackman and Eastop, more than 500 species of Aphis are currently recognized.
That’s a lot– about 10% of all aphid species. One phenomenon I’ve observed over the years is that some Aphis species seem to come and go; some years a given species will seem to be everywhere its host grows, then for years afterward it seems to be incredibly rare. That is the case with A. lupini. I have only seen it a few times in all the years I’ve looked at Lupinus in the west, yet in a couple years it has been very common. In fact, in one year I found a population of what appeared to be this species that was bright orange like Aphis nerii. As noted in the photo, this is a species with wingless (apterous) males.
Aphis neogillettei Palmer
With about 10% of all aphids in the genus Aphis, that’s a lot. This is yet another species that is fairly easy to recognize if you know the host (Cornus stolonifera) and the broad geography. It seems to live throughout the season on this plant. It occurs widely in North America and I have collected it in Oregon, Idaho, Montana, and Wisconsin.
Aphis pentstemonicola Gillette & Palmer
This species I have collected here and there for a long time, and sometimes confusing it with Aphis carduella, which also feeds on Penstemon in the mountains of western North America. This is one of many aphids that is most recognizable in life because of a color pattern that is entirely in the internal tissues that dissolve in the slide-mounting process. In the photo here, the distinctive dark blotch in the anterior abdomen is unusual and diagnostic.
Aphis phaceliae Gillette & Palmer
For many years this aphid was an exciting find, because although I looked at lots of Phacelia, this species of aphid was rarely found. During the 2016 season I found that it can reasonably consistently be found on Phacelia in the spring growing in dry disturbed soil such as south-facing road-cuts, recent timber harvest, etc. It is monoecious and I suspect it has an abbreviated life cycle, but have not been able to demonstrate the latter.
Aphis rubifolii (Thomas)
This is a fairly common species on blackberries, genus Rubus, in western North America where we lurk. The trick to finding it is that it can be very small indeed, with adult apterae commonly less than 1 mm long. I say it’s common, yet I have only 2 samples in my collection. The reason is likely that I often pass by common species without collecting them. I am trying to break this habit at least to some degree.
Aphis spiraecola Patch
Travel almost anywhere in temperate, subtropical, and tropical Earth and this species is there.
I usually carry a couple vials when traveling to Florida, Arizona, or Texas for work-related trips in winter. When really desperate to make a winter aphid collection, I can almost always find this species in these southern states. In the Northwest it can be incredibly abundant on ornamental Spiraea and is sometimes one of the most commonly trapped aphids in agricultural areas. It lived throughout the season in our Idaho garden on various ornamental Rosaceae. It can be a nice apple-green to bright yellow.