Pleotrichophorus

Pleotrichophorus Börner

This page updated: November 2025.

This genus is one of my favorites. Many of its species are charismatic in some way, being excellently camouflaged, or being gaudy in color, or being especially fleet-of-foot. They are also terribly frustrating to photograph largely because of the latter trait. It seems like they, as with most aphids living on desert shrubs, are disturbed as soon as their host plant is jostled and especially once their leaf or sprig is clipped off.  Once disturbed they stubbornly refuse to hold still for photos.  There are many described species of Pleotrichophorus, and it seems to me that most of the accepted species are valid and recognizable in the field and on slides. The genus lives mostly on Asteraceae, and mostly on shrubs and perennial herbs in xeric habitats such as sagebrush (Artemisia) and rabbitbrush (Ericameria and Chrysothamnus).

Pleotrichophorus ex Achillea from Hell's Canyon, Idaho.
Pleotrichophorus ex Achillea from Hell’s Canyon, Idaho.

The revision of North American Pleotrichophorus by Corpuz-Raros and Cook (1974) is really excellent in my opinion, especially considering neither author had done very much collecting in the field.  After all my years of collecting this genus, I still find most samples fit fairly well one of the species concepts laid out in their paper.  If I had infinite time and money to publish on aphids, I would love to do a complete revisit of their paper, pointing out all the ways they were right, and the few ways I think their work could be improved.

One issue with the genus is that some pairs or groups of similar species are recognized from the same host in different geographic areas. Also, sometimes two species are recognized for very similar aphids that vary in one major character such as length of siphunculi or a particular ratio of body part lengths. Based on my extensive collecting, I think close examination will reveal some of these species names to be applied to regional or host-plant variants of more widely distributed and variable species. An example of this issue are the species found on Achillea across North America (see P. patonkus below).

During fall of 2020 I made an effort to sort my material of several Pleotrichophous species including P. brevinectarius, P. gnaphalodes, P. decampus, P. zoomontanus, and P. quadritrichus. Sorting was made easier by having accumulated much material from all over the western U.S. What I found was that my identifications were mixed, and some of these ‘species’ were mixtures of 2, 3, or even 4 species that are actually fairly easy to recognize with adequate experience and comparative material (which I now have). These changes in identification were reflected in my 2021 release of the slide collection database.

In addition to the possibly erroneous splitting of geographically isolated populations of this genus into separate species, I consider another issue equally concerning: that some relatively distinctive ‘species’ that feed on several different plant species may be groups of similar-looking host-specific species. Examples of this phenomenon are what I had been calling P. brevinectarius and P. quadritrichus. There seem to be small but consistent differences in these ‘species’ based on Artemisia species they developed upon.

For several years I have been gathering samples of Pleotrichophorus from a native weedy plant called Iva axillaris (poverty weed). I have found this aphid in several western states. Since moving to Colorado I have it more or less in the front yard. When first found I ran it through the Corpuz-Raros and Cook key and it came out at P. parilis. At the time I lacked samples of this species from its previously known host, Artemisia dracunculus. Having found P. parilis on the latter plant in recent years, I decided in January 2024 to examine whether the form from I. axillaris can be consistently separated from P. parilis. The answer was, to my surprise, an easy “yes.” So, at some point I have at least one new species of Pleotrichophorus to describe!

According to what I can glean from Aphid Species File, there are 60 recognized species of Pleotrichophorus worldwide and about 44 of those are of North American origin. Because I have collected and studied this genus so much over the years, I thought I’d annotate everything in my collection much as I did for Illinoia and Macrosiphum. So below I will list and briefly discuss all 33 species I have identified in my collection, then all the recognized North American species I have not yet identified, then all my putative undescribed species.

Species covered below (click on the name to jump to that species):

Pleotrichophorus ambrosiae Hille Ris Lambers

This species is a bit of a puzzle for me. I have several samples that key out to this species, but they vary morphologically and in host plant more than I would expect. It was described by Hille Ris Lambers in 1969 based on material from Pennsylvania, the aphids living on Ambrosia artemisiifolia. I have a few samples from Ambrosia in Colorado and New Mexico, plus one sample I recorded as from Phacelia in the desert of central Washington. Because Ambrosia commonly grows in the same place as Phacelia in that locality, it is possible my specimens were casuals or my collecting technique was indiscriminate. Both Hille Ris Lambers and Corpus-Raros and Cook (1974) discuss the several similar species that have been variously lumped in the past. Their work might deserve to be revisited with all the recent material I have accumulated.

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Pleotrichophorus amsinckii Richards

This is an example of a species where my collecting and taxonomy has cast some uncertainty on an aphid’s biology.  This species was originally described from Amsinckia intermedia in British Columbia, but since then I have collected it on Phacelia and Eriophyllum.  As always with cases like this, it is possible that I misidentified the samples, but the unique morphology of this species is hard to miss.  Still, the possibility of undescribed species with unusual morphology similar to P. amsinckii cannot be ignored.  I also have a very similar, possibly undescribed, species from Arizona that was living on a Cirsium in the mountains. My samples of P. amsinckii are all from Oregon and Washington.

Pleotrichophorus amsinckii on Phacelia in central Washington.
Pleotrichophorus amsinckii on Phacelia in central Washington.

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Pleotrichophorus brevinectarius (Gillette & Palmer)

Described in 1933 based on specimens collected in southern Colorado, I covered my thoughts and experience with this species in some detail in my essay titled, “A Brief Study of the Very Short Siphunculi Section of the Corpuz-Raros and Cook Key to Species of Pleotrichophorus.” See that essay for photos of slide mounted material and much discussion of the taxonomy and history. I have about 80 slides in the box dedicated to this species, with samples from Washington, Oregon, California, Idaho, Nevada, Utah, Colorado, North Dakota, and New Mexico.

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Pleotrichophorus decampus (Knowlton & Smith)

This is one of the common species of Pleotrichophorus most places I go in western North America.  It lives on shrubby Artemisia.  If I had learnt my sagebrush taxonomy a long time ago, I could tell you more about what species of sagebrush. Fortunately I have learned enough to tell you something: this aphid seems to have a broad host range of shrubby Artemisia including A. arbuscula, A. californica, A. cana, and A. tridentata (including at least two of its subspecies). I have a few samples that I recorded as being from herbaceous Artemisia, and they conform well with the morphology of samples from shrubby hosts. I’m not sure what to think about that.  I have samples from Washington, Oregon, California, Idaho, Nevada, Utah, Colorado, Wyoming, and New Mexico.

Pleotrichophorus decampus on sagebrush in eastern Oregon in May.
Pleotrichophorus decampus on sagebrush in eastern Oregon in May.

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Pleotrichophorus diutius Corpuz-Raros & Cook

This is another of the not particularly distinctive species of this genus living on miscellaneous plants. They feature medium everything, with subtle distinctions among them. This species was named in 1974 based on a handful of samples from Minnesota and Colorado, living on Artemisia dracunculus and Artemisia sp. I have identified this species 4 times, all but one time was before I learned how to recognize Artemisia dracunculus and 3 samples were therefore noted as living on Artemisia sp. My samples are from Oregon, Colorado, and New Mexico.

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Pleotrichophorus elongatus (Knowlton)

Described in 1929, this is a reasonably recognizable species that feeds on rabbitbrushes (Ericameria and Chrysothamnus). Corpuz-Raros & Cook do a nice job of drawing distinctions between this species and the similar P. palmeri. I have identified it several times, and my material seems to agree with Corpuz-Raros & Cook. My samples are from Washington, Oregon, California, Nevada, and Colorado.

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Pleotrichophorus filifoliae (Palmer)

This species was described in 1938 based on material from northwest of Denver, Colorado, collected on Artemisia filifolia. I covered this species in some detail in my essay, ” “A Brief Study of the Very Short Siphunculi Section of the Corpuz-Raros and Cook Key to Species of Pleotrichophorus.” See that essay for photos of slide mounted material and discussion of the taxonomy and history. Specimens I have identified as this species after the study that went into this essay were all collected from A. filifolia. My samples are from New Mexico and Utah.

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Pleotrichophorus glandulosus (Kaltenbach)

This species is native to Europe but was introduced to eastern North America. It lives mostly on Artemisia vulgaris, one of the herbaceous members of the genus. I have one sample, collected in New Brunswick, Canada.

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Pleotrichophorus gnaphalodes (Palmer)

This is one of a few species that live Artemisia that I have struggled with taxonomically over the years. It was described by Miriam Palmer in 1938 based on a single sample of 50 specimens collected on Artemisia ludoviciana in Pingree Park, Colorado (a mountain location) in late August. Corpuz-Raros & Cook of course also covered this species, including material from several western and mid-western states of the U.S.A. Despite having studied the taxonomy reasonably well, I think my samples of this species may still be a mix of species. Some day I need to revisit my work on it, especially comparing all the various mid-range, average-looking species we have in this part of the country. My material was found living on various herbaceous Artemisia from low elevation deserts to mid-elevation (i.e., between 5,000 and 10,000 feet elevation) mountain habitats. I have samples from Washington, Oregon, California, Idaho, Nevada, Utah, and New Mexico.

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Pleotrichophorus gregarius (Knowlton)

This species was described by G.F. Knowlton in 1929 based on samples from several places in Utah and one in Idaho. It feeds on rabbitbrushes, now placed in the genera Ericameria and Chrysothamnus. The description and figures were unusually good for Knowlton in those days! Its morphology and coloration on slides is fairly distinctive (apart, apparently, from Pleotrichophorus xerozoous (Knowlton & Smith)). And, as the species name implies, it does often occur in large aggregations that are very evident to passersby. Most other members of this genus are rather cryptic, not easily seen before shaking them from their host plant. All my samples were found on Ericameria in Idaho, Utah, Nevada, Arizona, and New Mexico.

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Pleotrichophorus heterohirsutus (Gillette & Palmer)

This was an interesting description by Gillette and Palmer that matches well with my few samples. They collected 1 apterous vivipara, many oviparae, and 1 apterous male 17 September 1932 in Larimer County, Colorado. The specimens were recorded from Artemisia tridentata. While the species name implies variation in setae, I see more such variation in the ovipara than I have in my few apterae. Looking at their drawing of the head of their aptera, it seems also to have relatively uniform setae. I wonder if Gillette and Palmer chose the species name based on the setae of the ovipara, which was the primary morph at their disposal. Anyhow, the species has unusually low antennal tubercles, oddly variable setal shape, and short-ish siphunculi. I have identified this species only 3 times, in New Mexico and Colorado.

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Pleotrichophorus infrequenus (Knowlton & Smith)

It was only during the work on this website project that I decided to recognize a couple samples as this species. Originally described from the hills east of Salt Lake City, Utah, I had not recognized this species in all these decades of collecting on sagebrushes. I decided to look through my undetermined material and concluded that the 2 samples I have from Artemisia bigelovii near our house in western Colorado may be this species. It is distinctive by having very short siphunculi and a relatively long R IV+V. Note, however, that the final couplet to this species in Corpuz-Raros & Cook (1974) incorrectly states that the R IV+V is at least 1 2/3 times the length of HT II. Looking at her own measurements, we see that the ratio is closer to 1.25 times, very similar to the specimens I decided at call P. infrequenus. It looks like A. bigelovii does not occur as far north as the type locality, so the plant was likely A. tridentata as reported. It is reasonable to wonder, then, whether there is one or 2 species involved. I guess I need to collect more on sagebrushes near Salt Lake City.

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Pleotrichophorus lagacei Hille Ris Lambers

Hille Ris Lambers (1969) described this species from the Mount Shasta area of California where it was recorded as feeding on Haplopappus bloomeri, which is apparently now considered to be an Ericameria. It is unusual for the genus in having siphunculi with the apical part distinctly swollen. I have found this species 3 times, all in southeastern Oregon on plants I recorded as Chrysothamnus. I fully admit that my taxonomy skills are poor when it comes to species-level identification of rabbitbrushes and similar, especially at high elevations where they seem to show wide morphological variation.

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Pleotrichophorus longinectarius (Gillette & Palmer)

This species takes us to an interesting place, Chimney Rock, Colorado, famous for the ancient human settlements there. Gillette and Palmer’s work there interested me in 2025 because they recorded some species, including this one, as living on Artemisia longifolia there. I was 99% certain that their plant identification was wrong because the botanists do not recognize A. longifolia as occurring anywhere near there. So, we traveled there and had a look. The common sagebrush in that area is Artemisia cana (silver sage), which has long undivided leaves. It has obviously been confused by aphidologists (all of us amateur botanists) with A. cana over the years. As noted by Corpuz-Raros & Cook this species can be recognized by the long siphunculi, short cauda, and long very thin and pointed R IV+V. I have one sample of 2 specimens from northern New Mexico that fit these features very well. I collected it in 2010 and recorded the host as, “Artemisia – low, with highly compound leaves.” This was before I learned to recognize most sagebrush species, and I am reasonably certain that what I had was Artemisia frigida. But, we’ll never know for sure.

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Pleotrichophorus longipes (Gillette & Palmer)

This is an unusual species, originally described by GIllette & Palmer (1928) in the genus Macrosiphum. It has few of the features common to other species of Pleotrichophorus, the sparse and pointed setae on body and head are especially unusual. Its mouthparts are typical of many of the aphids that feed on rabbitbrushes across Pleotrichophorus and Aphis (Zyxaphis). It was transferred to Pleotrichophorus by Hille Ris Lambers (1969) without comment or justification — he simply included it in a key to species of Pleotrichophorus. Including species like this in the genus makes defining Pleotrichophorus based on shared morphological features nearly impossible. That’s how different it is. I have even considered whether this species is more closely related to Epameibaphis and Pseudoepameibaphis than it is Pleotrichophorus. Dorsal chaetotaxy is similar to Epameibaphis, and the weirdly shaped siphunculi with a slight apical swelling are also suggestive to me. Bottom line is that it is very much an outlier among Pleotrichophorus species.

This species is large, fast running, and sometimes very colorful — the first time I found it the specimens in the area were a bright bluish/turquoise color. Very striking. It is recorded in the literature as feeding on Artemisia tridentata. I have it mostly from the form of this species known as “mountain sagebrush” plus a couple samples that I thought were on the more xeric-adapted form of A. tridentata known as “Wyoming sagebrush.” I have also gotten samples from Artemisia arbuscula. My samples are from Washington, Oregon, California, Idaho, Utah, Wyoming, Colorado, and New Mexico.

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Pleotrichophorus longirostris Hille Ris Lambers

Described in 1969, this species feeds on Eriophyllum staechadifolium and Eriophyllum lanatum. It is distinctive in having a very long R IV+V, about as long as the short, lightly pigmented siphunculi. This long R IV+V seems to be an adaptation to living on this plant genus – the other common host-specific aphid on Eriophyllum, Macrosiphioniella sunshine, also has an extraordinarily long R IV+V. I’ve collected it quite a few times, including oviparae and alate males, all in Oregon and Washington.

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Pleotrichophorus magnautensus (Knowlton & Smith)

Here is another example of why it is useful to make these lists of species I have and to look carefully at the species I have never identified. As I worked on what I would say about this species below in the section for species not yet identified in my collection, I noticed that this was probably the correct identification for a sample I got in 2024 from along the Price River in Utah. The feature that sent me astray in the key by Corpuz-Raros & Cook (1974) is the mention of “numerous” minute hairs on the ventral surface of a.s. I and the head. My 2 specimens lack such hairs but conform perfectly otherwise. While the hairs are indeed minute, they are no more numerous than usual for this genus, i.e. about 6 on a.s. I and about 12 on each side of the head. These are not in rows as mentioned by Corpuz-Raros & Cook and Knowlton and Smith. It is of course possible that my specimens represent a similar undescribed species, but I am opting for P. magnautensis for them.

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Pleotrichophorus obscuratus Hille Ris Lambers

This is another of the species I discussed in my essay titled, “A Brief Study of the Very Short Siphunculi Section of the Corpuz-Raros and Cook Key to Species of Pleotrichophorus.” See that essay for a photo of a slide mounted specimen and much discussion of the taxonomy and history. I am still not certain that what I call P. obscuratus is conspecific with what Hille Ris Lambers (1969) had, but it’s the name I’m going with for now. My material is from Oregon, California, Idaho, Utah, Nevada, Wyoming, and Colorado.

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Pleotrichophorus oestlundi (Knowlton)

One of the most common species of Pleotrichophorus, this one is also easily identified. Living on rabbitbrushes (Chrysothamnus and Ericameria), it is unusual for this genus in having extra setae on the top of the cauda.  I have collected it in Washington, Oregon, California, Idaho, Nevada, Utah, Colorado, Wyoming, New Mexico, and Arizona.

Pleotrichophorus oestlundi from southern Idaho.
Pleotrichophorus oestlundi from southern Idaho.
Pleotrichophorus oestlundi from southern Idaho, showing a common feature for this genus: relatively dark and prominent veins in the wings.
Pleotrichophorus oestlundi from southern Idaho, showing a common feature for this genus: relatively dark and prominent veins in the wings.

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Pleotrichophorus packi (Knowlton)

Another Knowlton (1928) species, this one described based on a single alate vivipara despite his claiming to have seen the species from numerous locations in Utah. It has been interesting to go through my samples of Pleotrichiphorus, reminding myself of the species and samples I have. This one was surely a pain to identify since the specimens I have go astray in the key by Corpuz-Raros and Cook on the second couplet. This couplet divides off several species based on having relatively short setae on the basal part of R IV+V, this species going toward the side of the couplet for longer setae (2 times or longer than more apical setae). Yet, in the descriptive notes of the species they say that apical setae are about 2/3 the length of the basal ones, not 1/2 or less. This is an error in the key. However, if you push this species to the wrong (right?) side of the key and forge ahead with it, we arrive at P. packi. I have identified this species only twice, both times from New Mexico; apparently it is common in Utah.

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Pleotrichophorus palmerae (Knowlton)

This species was described by Knowlton in 1935 based on an unknown number of apterae collected in June in Tahoe National Forest, California. The species lives on rabbitbrushes, genus Ericameria. It has few really distinctive features, but all features combined have allowed me to identify it quite a few times. I have samples from Washington, Oregon, California, Idaho, Nevada, and Utah.

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Pleotrichophorus parilis Corpuz-Raros & Cook

This is one of many Pleotrichophorus species that I think can be easily confused — medium almost everything in terms of morphological features. Corpuz-Raros & Cook had many specimens of this and some of the other comparable species and provided detailed diagnostic notes. Some day I need to study their key and notes for all these similar species to see if I can understand and agree with their thinking. This species is known to feed on Artemisia dracunculus, from which I have collected it. I also identified my material from Ixa axillaris (see below under putative undescribed species) as this species for a few years, but now I think it is separate. I have identified this species 4 times, all from Colorado.

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Pleotrichophorus patonkus (Hottes & Frison)

Almost everywhere I see Achillea in the wild, aphids I identify as P. patonkus are present.  There are two other very similar described species from Achillea in North America (P. patonkusellus and P. pseudopatonkus), and they are not obviously distinct from P. patonkus.  I made a new attempt at sorting my material of this group during fall of 2020. I recognize that there is a good range in length of siphunculi, shape and length R IV+V, and density of dorsal setae. However, the variations I see do not match up well with the features as reported in the primary literature. The most extreme character states are my samples from Maine and Quebec, which have rather short R IV+V and siphunculi, and sparse dorsal setae. All my other samples are similar to each other in terms of denser dorsal setae, but vary a bit in terms of R IV+V. Their dorsal setae, however, are not as dense as in the description of P. patonkusellus and in fact most bob around very close to the typical number for P. patonkus mentioned by Corpuz-Raros and Cook (1974). I tend to be a lumper in this case due to the apparent variation in characters thought to distinguish between the three “species.” 

I have samples of this group from Washington, Oregon, California, Idaho, Utah, Colorado, New Mexico, Maine, and Quebec, but I have walked by many other possible collections due to the ubiquity of these aphids.  As always, failing to collect samples is probably a mistake since it skews our understanding of common species.  For example, the common house fly is hardly ever collected due only to its ubiquity.

Pleotrichophorus patonkus from the Snake River's Hells Canyon in April. Look at those nymphs embedded in the leaf hairs!
Pleotrichophorus patonkus from the Snake River’s Hells Canyon in April. Look at those nymphs embedded in the leaf hairs!

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Pleotrichophorus pseudoglandulosus (Palmer)

This is a key species I identify from herbaceous members of Artemisia from across western U.S.A. Palmer (1952) described it based on material from Colorado, Idaho, and Utah. I find it to be similar to P. decampus, and have confused the two in the past (and my collection may still have mixtures of the two species). It looks like P. decampus feeds on shrubby Artemisia, especially A. tridentatae, while P. pseudoglandulosus feeds on herbaceous Artemisia species. I have material from Washington, Oregon, California, Idaho, Nevada, Utah, New Mexico, and Colorado.

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Pleotrichophorus pullus (Gillette & Palmer)

This is another species with some host plant and locality confusion. Gillette and Palmer described it in 1933 based on specimens collected at “Chimney Rock.” Because of the title of the paper, “New Species of Aphids from Colorado,” we assume that this Chimney Rock is in Colorado. However, if we look at Palmer (1952), one of two localities for this species is given as “Colorado-Wyoming line at Chimney Rock (near Jelm, Colorado).” She mentions nowhere the locality of the original types, Chimney Rock, Colorado, which is in the south, just north of New Mexico. The uncertainty here is whether Palmer was adding a locality, i.e. Chimney Rock, Wyoming to the species, or was either this reference or the Gillette and Palmer locality incorrect? If we look at Jelm, Wyoming we see that near there to the west is Chimney Park. Looking for Chimney Rock, Wyoming, that is located about 50 miles northeast of Jelm. Because Palmer (1952) goes to the trouble to note that the locality is near Jelm and near the Colorao-Wyoming border, I suspect she was writing of Chimney Park. Anyhow, I think you see my point. Uncertainty reigns.

Gillette and Palmer and Palmer recorded the host as Artemisia longifolia. As noted elsewhere, A. longifolia does not occur around Chimney Rock in southern Colorado, with Artemisia cana being the common species and likely to be confused with A. longifolia because of their similarly-shaped leaves. Given the confusion noted above under P. longinectarius, I suspect that true type host of this species was Artemisia cana.

This aphid is fairly distinctive, with dense, short expanded setae, some of which are long and pointed on the head, the antennae have unusually long and pointed hairs. It tends to live in large aggregations and is easily seen from a distance, an unusual feature among Pleotrichophorus. I have seen it tended by ants at least twice, also unusual for the genus. My material is from Oregon and Idaho, feeding on Artemisia tridentata (mt. sage) and A. cana.

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Pleotrichophorus pycnorhysus (Knowlton & Smith)

This species is relatively easy to recognize due its sparse dorsal setae (sparse for Pleotrichophorus, that is).  Most of my samples are from what is known as green rabbitbrush, Chrysothamnus viscidiflorus, and the samples from other rabbitbrushes may well have been in error, vagrants, etc.  This is an example of a Pleotrichophorus species that seems to be quite variable in terms of length of siphunculi.  I so far have samples from Washington, Oregon, Idaho, Utah, and Nevada .

Pleotrichophorus pycnorhysus fundatrix in central Washington living on Chrysothamnus viscidiflorus.
Pleotrichophorus pycnorhysus fundatrix in central Washington living on Chrysothamnus viscidiflorus.
Pleotrichophorus pycnorhysus apterous vivipara from the Boise, Idaho area, once again on green rabbitbrush.
Pleotrichophorus pycnorhysus apterous vivipara from the Boise, Idaho area, once again on green rabbitbrush.

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Pleotrichophorus quadritrichus (Knowlton & Smith)

This active species is common and widespread in western North America, and is relatively easy to recognize in part by its dark siphunculi and cauda. It lives on shrubby Artemisia (sagebrush). During fall of 2020 I looked through all my material of this species and sorted them according to host plant species: A. arbuscula, A. cana, A. rigida, and A. tridentata (at least two subspecies). There are subtle but consistent morphological differences based on host plant, such as length of antennal setae, density of dorsal setae, shape of the R IV+V, and leg pigmentation. Since moving to Colorado in 2021 I have also found this ‘species’ on Artemisia nova and Artemisia bigelovii. Perhaps another self-funded graduate student would want to drive all over the west making collections on known species and subspecies of Artemisia to sort all this out!?

I have samples from Washington, Oregon, Idaho, Nevada, Utah, Wyoming, Colorado, North Dakota, and New Mexico.

Pleotrichophorus quadritrichus from central Washington.
Pleotrichophorus quadritrichus from central Washington.

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Pleotrichophorus spatulavillus (Knowlton & Smith)

Knowlton and Smith described this species in 1936 based on material from Washington County, Utah and southeastern Idaho, where it was recorded as living on Artemisia tridentata and Artemisia sp. It has relatively short siphunculi, like many other species discussed here, but its typical Artemisia-feeding R IV+V helps make it recognizable. I have identified this species several times, with samples from Oregon, Idaho, Wyoming, and New Mexico.

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Pleotrichophorus stroudi (Knowlton)

Another unusually recognizable species, P. stroudi was described in 1948 based on material collected in June and August 1947 at White Sands in New Mexico. It feeds on rabbitbrushes, in my experience the Ericameria forms with greenish stems and greyish foliage. Its extremely long siphunculi, large body size, dark antennae, etc. are distinctive. My samples are from Oregon, Idaho, Utah, Colorado, and New Mexico.

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Pleotrichophorus tetradymiae Smith & Knowlton

Here is an aphid I sought for so many years that I lost track.  From the description, it seemed like it would be an oddball, and sure enough it is, living on its uncommon host, Tetradymia canescens in the sagebrush steppe.  Blackman and Eastop’s notes on it seem to imply that they did not believe the color-in-life notes from the literature, but here it is, in its “blackish green” color.  I have only seen this aphid a couple times, in Oregon and Idaho.

Pleotrichophorus tetradymiae on Tetradymia canescens near Lakeview, Oregon in September.
Pleotrichophorus tetradymiae on Tetradymia canescens near Lakeview, Oregon in September.

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Pleotrichophorus utensis (Pack & Knowlton)

Rare finds like this species are one of the things that keep me interested in pounding on rabbitbrushes everywhere I go.  I have seen this species only a few times now in over 25 years of collecting aphids on rabbitbrushes, its hosts. In 2024 I found some oddball specimens that are similar to, but different from, this species, indicating things may be more complicated than previously known. I have samples from Washington, Oregon, Idaho, and Utah.

Pleotrichophorus utensis, possibly a fundatrix, on green rabbitbrush in southern Idaho in April.
Pleotrichophorus utensis, possibly a fundatrix, on green rabbitbrush in southern Idaho in April.

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Pleotrichophorus villosae Robinson

Robinson published this species in 1974, thereby creating a shortcoming in Corpuz-Raros & Cook’s paper, which came out the same year and was not able to cover P. villosae. This species is another of the medium-sized-and-bland-everything species of Pleotrichophorus that includes a couple possible new species. I need to someday sit down and really come to terms with the taxonomy of these similar species. I have collected P. villosae at fairly high elevations in the mountains (plus one site in Denver) of Colorado and New Mexico on Heterotheca, probably the species H. villosa.

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Pleotrichophorus zoomontanus (Knowlton & Smith) 

I don’t have a photo of this large and fast-running species, but I wanted to briefly touch on it anyway. I’ve collected this species quite a lot over the past decade or so, and after a 2020 careful sorting of my samples of long-siphunculi Pleotrichophorus from Artemisia I showed that P. zoomontanus lives exclusively, or nearly so, on Artemisia cana, not A. tridentata as previously thought. A couple of my samples are marked as from A. tridentata, but these were from a time before my ability to identify species of Artemisia had developed. I have samples from Washington, Oregon, California, Nevada, Utah, Wyoming, and Colorado.

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Recognized species of North American Pleotrichophorus not yet identified in my collection:

Pleotrichophorus antennarius Corpuz-Raros & Cook: described in 1974 based on a single sample composed of 6 apterae, 5 oviparae, and 2 apterous males. The specimens were found in Washington D.C., 14 October 1894, feeding on Antennaria. This seems to be the only known sample of this species. I see Antennaria very frequently in my collecting outings, but have never seen a Pleotrichophorus on it. I wonder whether the plants used by these aphids were native in a natural system or were cultivated ornamentals. At this point, 130 years later, it is very hard to find natural systems in the D.C. area to attempt re-collecting of rare species found by Pergande and others in the late 19th century and early 20th century.

Pleotrichophorus artemisicola (Williams): a very interesting situation exists with this species. It was not covered by Corpuz-Raros & Cook (1974), In fact, it appears that this species has never been covered beyond nomenclatural lists since it was described in 1911. Williams’ description is nice in terms of overall appearance of the aphids, but is useless in terms of modern taxonomy of the group. This species, therefore, is not recognizable until the types are seen and more thoroughly documented.

Pleotrichophorus asterifoliae (Strom): another strange case, this species has been shuffled between the genus Acyrthosiphon and Pleotrichophorus since it was described in 1934. It has been included in one key to species of Acyrthosiphon and has otherwise appeared only in lists. The original description is not useful for recognizing this species among currently known Pleotrichophorus. So, without seeing types or specimens collected somewhere near the original locality in Wisconsin, I can’t comment much on this species. According to Strom it lived on the lower leaves of an Aster species growing in the shade. This is unusual biology, so this species will probably easily recognized once I find it.

Pleotrichophorus blackmani Barjadze, Halbert & Kanturski: this species is the only member of Pleotrichophorus described as new in North America for the past 50 years. It lives on Euthamia in Florida and presumably nearby areas. Its morphology is not typical of the genus, having straight, sparse, blunt or slightly capitate setae and a broad parallel-sided R IV+V. A key feature shared with other Pleotrichophorus is the 2 pairs of lateral setae on the cauda. The authors of this species attempted some DNA analyses that were interestingly hampered by a paucity of DNA finger-printed Pleotrichophorus in existing databases.

Pleotrichophorus hottesi Hille Ris Lambers: this species was described in 1969 based on a handful of specimens collected near Grand Junction, Colorado (i.e., about 50 miles from my house) in September of 1965. It was reported as feeding on Achillea and as being distinctive among Pleotrichophorus on that plant genus by having much longer siphunculi. It is odd that despite decades of tapping on Achillea I have never seen this species. Maybe I need to look for it next time we visit Grand Junction!

Pleotrichophorus knowltoni Corpuz-Raros & Cook: this species was described based on a handful of specimens collected from an unknown host at Umiat, Alaska in July of 1955. This location is very near the northern extreme of Alaska, beyond 69 degrees north latitude. In 2015 Stekolshchikov and Khruleva wrote about specimens found living on Artemisia tilesii in eastern Siberia and provided detailed descriptions of the fundatrix and apterous male. Given its native habitat, I am unlikely to collect this species in my life time. But, who knows, maybe it lives in high mountains in the lower latitudes I frequent.

Pleotrichophorus neosporadicus Corpuz-Raros & Cook: apparently this species is so similar to P. sporadicus that Blackman and Eastop were unable to find differences useful in their keys. Only 2 specimens were used in the description of P. neosporadicus, collected at Promontory, Utah, living on Ericameria nauseosa.

Pleotrichophorus ohioensis Smith: described in 1940, this species was found on the underside of leaves of a Helianthus species in Columbus, Ohio. Smith had numerous specimens and prepared a pretty good description. This species has since only appeared in keys and lists (except Corpuz-Raros & Cook, but they only rehashed what Smith had written based on his types), it being unclear whether it has ever been collected since Smith’s work in the 1930s.

Pleotrichophorus sporadicus (Knowlton): as noted above, this is one of a couple or more very similar forms that live on rabbitbrushes (Ericameria, Chrysothamnus) in the western U.S. It is strange I’ve never identified it, but I can’t find any wayward specimens that perhaps should have this name. Once again,. I may need to visit the type locality (the area between Salt Lake City and Logan, Utah) to find it and learn what the heck it looks like.

Pleotrichophorus triangulatus Corpuz-Raros & Cook: originally reported as feeding on Agoseris south of Lake Tahoe, California, 18 August 1931. This is another species that seems to have rarely if ever been collected since the original description. For 30+ years I have avidly looked for aphids on Agoseris and similar Asteraceae without finding any Pleotrichophorus. It is apparently a distinctive species, with a very short triangular R IV+V.

Pleotrichophorus wasatchii (Knowlton): I have seen this species mentioned left right and center during this project expanding my Pleotrichophorus page, with the apparently many similar species being compared to it. It is odd that I’ve never recognized it. It feeds on rabbitbrushes currently placed in Ericameria and maybe Chrysothamnus. Looking at the material presented by Corpuz-Raros & Cook (1974), I wonder whether there is something amiss with their key to species that causes me to end up with other determinations such as P. palmeri (I have uncovered at least 2 other major mistakes in their key, so this is a reasonably likely option).

Pleotrichophorus xerozoous (Knowlton & Smith): this is apparently another species name used for some specimens that were different from, but very similar to, members of a previously well-established species. In this case the similar species is P. gregarius, and Blackman and Eastop note that P. xerozoous may represent seasonal variants of P. gregarius.

Putative undescribed species of Pleotrichophorus in my collection:

Unidentified species on Erigeron near Montrose, Colorado: In September of 2024 I collected several specimens from an Erigeron species on Cerro Summit east of Montrose. The specimens are unusual in having sparse but short and broadly expanded dorsal setae, a blunt and nearly parallel-sided R IV+V, apically curved siphunculi, rugose antennal segment I, and a rugose patch on the ventral side of the antennal tubercle. All my specimens are apterous viviparae.

Unidentified species on Tetradymia near Montello, Nevada: Driving along a desolate highway in eastern Nevada in 2016, I stopped on the side of the road and collected a series of dark-colored Pleotrichophorus specimens living on a Tetradymia species. These are weird for their long dark siphunculi, akin to P. quadritrichus, and long setae on the antennae. It is possible that I misidentified the host plant, but I remember being fairly confident that it was a Tetradymia.

Unidentified species living on Cirsium north of Flagstaff, Arizona: this was collected during a long expedition/vacation with my sons in 2004 (they were then 14 and 12 years old). I was focused on Cirsium (a.k.a. thistles) on that trip since I was working Bipersona. I remember looking at some Cirsium from my car window as we drove along a gravel road in the mountains, seeing this Pleotrichophorus living abundantly on the flower stems of an unidentified Cirsium. It has an incredibly long and thin R IV+V and does not conform to the other species that have this feature.

Unidentified species living on Ixa axillaris acros western U.S.A.: I mentioned this form above under P. parilis because for a while this was the name I used for specimens found on Iva axillaris. I have subsequently decided that the morphology may be sufficiently distinct to consider it a separate species. It is one of the several Pleotrichophorus species that have medium everything and are frustratingly similar. Its host, Iva axillaris (a.k.a. poverty weed), is a native species that grows in disturbed sites and along roads much like many invasive weeds. This species is usually greenish and has pinkish apterous males. I have about 50 slides of this species, including all morphs, from Washington, Oregon, California, Utah, Wyoming, and Colorado.