Macrosiphum Passerini

Macrosiphum is my favorite aphid group, getting my start on its diversity and field biology way back in undergraduate years with exploration of the first host alternation of a fern-feeding species. In those days Sitobion was still used for some of the species now considered Macrosiphum; this brings up the point that the name Macrosiphum is now used for what is likely a polyphyletic assemblage of species.  Some day it might turn out to be better thought of as 2, 3, or more genera.

Macrosiphum rhamni oviparous female
Macrosiphum rhamni oviparous female.

Jensen, A.S., J.D. Lattin and G.L. Reed. 1993. Host plant alternation in two fern-feeding Sitobion Mordvilko. in: Critical Issues in Aphid Biology: Proceedings of the 4th International Symposium on Aphids. P. Kindlmann and A.F.G. Dixon, eds. 142 pp.

Since then I finished a Ph.D. studying this group, and published 20 new species (so far, more to come).  My impression of this group is that there has been recent and rapid diversification, especially so in western North America.  There are many tightly host-specific species that are morphologically similar.  But you should be able to see from the coverage of species here on AphidTrek that Macrosiphum species come in many beautiful colors and live in some fabulous ecosystems.

Jensen, A.S. 2022. A new species of Macrosiphum (Hemiptera: Aphididae) living on Silene (Caryophyllaceae). Zootaxa, 5183 (1): 75–89.

Jensen, A.S. and J. Rorabaugh. 2020. New Macrosiphum Passerini (Hemiptera: Aphididae) Information from Western North America Including One New Species and One New Synonymy. Proceedings of the Entomological Society of Washington 122: 81-103.

Jensen, A.S., R. Peña-Martinez, A.L. Muñoz-Viveros, and J. Rorabaugh. 2019. A New Species of Macrosiphum Passerini (Hemiptera: Aphididae) from Mexico on the Introduced Plant Pittosporum undulatum. Proceedings of the Entomological Society of Washington 121: 39-53.

Jensen, A.S. 2017. Two New Species of Macrosiphum Passerini (Hemiptera: Aphididae) from Dry Forests of Western United States. Proceedings of the Entomological Society of Washington 119: 580-600.

Jensen, A.S. 2015. Two New Species of Macrosiphum Passerini (Hemiptera: Aphididae) From Western North America. Proceedings of the Entomological Society of Washington 117: 481-494.

Jensen, A.S. 2012. Macrosiphum (Hemiptera: Aphididae) Update: One New Species, One Synonymy, and Life Cycle Notes. Proceedings of the Entomological Society of Washington 114: 205-216.

Jensen, A.S. and C.K. Chan. 2009. Macrosiphum living on Fumariaceae in northwestern North America, including one new species (Hemiptera: Aphididae). Proceedings of the Entomological Society of Washington 111: 617‑626.

Jensen, A.S. and J. Holman. 2000. Macrosiphum on ferns: taxonomy, biology and evolution, including the description of three new species (Hemiptera: Aphididae). Systematic Entomology 25: 339-372.

Jensen, A.S. 2000. Eight new species of Macrosiphum Passerini from western North America, with notes on four other poorly known species (Hemiptera: Aphididae). Proceedings of the Entomological Society of Washington 102: 427-472.

Macrosiphum aetheocornum Smith & Knowlton

For some years this species was a major collecting goal of mine.  I collected on geraniums of all kinds for many years before finding this aphid for the first time in 2010 in New Mexico.  Since then, I’ve found it many additional times, including fundatrices and sexuales, proving monoecy.  I find it on what I call Geranium richardsonii, a plant that seems to have a wide variation in habitat preference and is irritatingly similar to G. viscosissimum where their ranges overlap.  This aphid seems to live only in the mountains, and I have specimens from Oregon, Idaho, Utah, New Mexico, and Arizona.

Macrosiphum aetheocornum from central Oregon in June.
Macrosiphum aetheocornum from central Oregon in June.

Macrosiphum albifrons Essig

This aphid is one of the largest in the world, and is actually familiar to many flower gardeners: it feeds on lupins (Lupinus) and is sometimes called the ‘lupin aphid.’ It is widespread in North America and has spread elsewhere as well with its cultivated lupin hosts.

Macrosiphum albifrons
Macrosiphum albifrons aptera

In natural systems, M. albifrons seems to be able to feed on many species of Lupinus, however, some samples seem to differ morphologically from others. I have suspected that more than one species may be involved, but have not had the time, resources, etc. to study the situation in detail.

One similar species is Macrosiphum zionense (see below), which lives on a lupin-like legume called Thermopsis in the mountains of inland western North America. M. zionense is usually yellow or orange and has dark antennae, siphunculi, and legs. Another nominal species, Macrosiphum thermopsaphis, was described from Thermopsis in Colorado back in 1938 by G.F. Knowlton. It was never recovered after the original collections and was sunk as a synonym of M. zionense in 1997.

During spring of 2024 I studied my samples identified as M. albifrons and M. zionense that were collected on Thermopsis. A key reason for this was to ascertain whether the pale green specimens I had collected over the years on Thermopsis were in fact M. albifrons as I had guessed. I was finally prompted to do this analysis by two collections in 2023 in which I found typical M. zionense with yellow/orange color and dark appendages together with specimens of the size and coloration of M. albifrons. Both forms were extremely abundant on large patches of Thermopsis, one in the La Sal Mountains of eastern Utah, the other in far western Colorado on Uncompahgre Butte. These sites are actually visible one from the other, perhaps 25 miles apart by air. Anyhow, looking at these samples of pale specimens on Thermopsis, it was clear that the specimens did not fit either M. albifrons nor M. zionense. They had fewer rhinaria on antennal segment III than M. albifrons, but more than M. zionense. Also, the fourth antennal segment was about the same length as the third segment. In short, the pale specimens on Thermopsis were easily separated morphologically from both other species. So, I referred to Knowlton’s original description of M. thermopsaphis. Here is what he said: “Apterous vivipara.-Color light green with a dorsal covering of grayish pulverulence… Taxonomy.- Macrosiphum thermopsaphis differs from M. zionesis Knlt. [sic] in having pale cornicles, shorter hind tarsi, and more secondary sensoria; it differs from M. albifrons Essig in possessing fewer sensoria on antennal III of aptera, and in antennal IV being almost equal to or longer than III, rather than 0.14 to 0.3 mm. shorter.” It turns out that my samples fit Knowlton’s notes perfectly. I therefore have labeled these slides and noted them in my collection database as M. thermopsaphis. This action is of course not an official nomenclatural change — it is for entertainment here on AphidTrek. Interestingly, I have a sample collected in the La Sal Mountains site from Lupinus at the same time. These are typical M. albifrons in terms of rhinaria and antennal segments. One of course wonders whether ‘M. thermopsaphis‘ could be of hybrid origin, but until the unlikely event that someone studies the issue, I think it best to highlight this distinct form using Knowlton’s name.

Macrosiphum albifrons aptera posing for her photo.
Macrosiphum albifrons aptera posing for her photo.

Macrosiphum badium Jensen

I studied this species extensively during my Ph.D. research in Oregon, where it was common in the forests living on Smilacina (a.k.a. Maianthemum, false lily of the valley). The description was published in 2000 when I wrote, “This species is monoecious, holocyclic, feeding on Maianthemum racemosa, M. stellata and M. dilatatum (Liliaceae). Egg hatch occurs during March in Oregon’s Willamette Valley as the plants are unfolding. Reproduction continues until June, when the apterae present at the time mature, and enter what appears to be a reproductive diapause through the summer. These apterae settle either among the fruits, when present, or on the lower leaves. Reproduction begins again in September, usually on the lower or most yellow leaves. The apterae that survive the summer give birth to oviparae and males. Eggs are laid below the surface of the soil along the plant stem. Males have only been observed in nature twice, despite many sincere efforts. The first apterous male was collected on the outside of a cloth bag enclosing a plant that had several oviparae on it. In 1994, males were quite easy to find throughout my normal collecting areas in McDonald State Forest. Some plants had several males, both alate and apterous. This occurred even though populations of the aphid overall were not dramatically higher than other years.”

In 2000 this aphid was only known from Washington and Oregon, but I have since collected it in Idaho and Montana.

Macrosiphum badium aptera from the Cascade Range in Washington.
Macrosiphum badium aptera from the Cascade Range in Washington.

Macrosiphum californicum (Clarke)

This is the name used for Macrosiphum feeding on species of Salix (willow).  Based on 30 years of collecting, it is clear to me that there are at least two species of Macrosiphum using Salix as host.  The main distinction between them is the number of setae on the cauda, but other features seem to vary by species as well.  The most common of the species is closely related both morphologically and ecologically to the Macrosiphum found on Cornus (dogwood) that is elsewhere thought to be M. hamiltoni (an idea I disagree with).  I have tried a couple host-plant transfers between Cornus and Salix, with interesting but not yet conclusive results.  Some of the specimens on Salix have bold dorsal internal stripes as in the photo below, while other specimens are a simple plain green with mostly dark siphunculi.  Check back in a few years, and maybe I’ll have published the results of my research on this group.

Macrosiphum on Salix from the Warner Mountains of Oregon in September of 2018.

Macrosiphum claytoniae Jensen

This is another of the 8 species I described in one paper that arose from my thesis research in 2000. Back then I wrote about it, “This species appears to be entirely anholocyclic. Hosts include Claytonia sibirica L. (Portulacaceae) and two other unidentified Claytonia spp. The former is the most important host. The aphid feeds throughout the year on its hosts, reproducing whenever temperatures allow. During the spring of 1992, normal apterae were found 29 February on a plant that had overwintered. Anholocycly was suspected at this

Macrosiphum claytoniae aptera from the forest at the edge of the Willamette Valley, Oregon.
Macrosiphum claytoniae aptera from the forest at the edge of the Willamette Valley, Oregon.

time, but was not proven until the winter of 1993 when sexuales were not recovered from field colonies and did not develop in the laboratory. Also during this winter there was a 15 cm snow fall followed by temperatures as low -8°C. During the last day that snow lay on the forest floor, aphids were observed under the snow in cavities formed by overlying fern fronds. Temperatures at the time were about 2°C, and aphids were capable of sluggish movement when prodded.

This species’ biology is unusual not only because it is anholocyclic, but also because its most important host plant is not a perennial. In McDonald State Forest, Benton County, Oregon, most C. sibirica plants germinate from seeds in the fall and winter, often becoming very dense as they flower in spring and early summer. By late summer, most plants have died, leaving only a few very robust ones in drier sites, and a few plants of various sizes near streams. Thus each year this aphid species experiences a very severe population reduction as its plants die out. It often survives the dry season on plants near streams or seeps. It must remain on these surviving plants until mid winter, when the plants are getting larger, and preparing to flower. In some years, this species is abundant and widespread in McDonald State Forest in late winter and spring.”

Macrosiphum claytoniae is known only from British Columbia, Washington, and Oregon.

Macrosiphum clum Jensen

A recently described new species, which I was alerted to by Blackman and Eastop’s books years ago.  After many years of hunting on various Clematis species (none of which I could initially identify to species), I finally stumbled on this aphid using my standard beating tray technique of 30×30 cm plywood and paint stirring stick, tapping haphazardly on Clematis ligusticifolia.

Macrosiphum clum fundatrix from above the Alvord Desert in eastern Oregon.
Macrosiphum clum fundatrix from above the Alvord Desert in eastern Oregon.

Subsequently, I learned to find this aphid fairly reliably, and finally described it in 2015.  In that paper I wrote, “This species lives in low densities on its host plant, mostly in exposed and dry or rocky sites. Numerous patches of C. ligusticifolia have been searched, and only a small percentage seem to host M. clum. Almost all collections of this aphid have been made by beating the plants over a wooden board. The aphids live so well-concealed on the leaves that the only time specimens were seen without beating was when they lived in some numbers on etiolated stems growing in the relative dark under a bridge near Weatherby, Oregon. Sites where M. clum was found were usually low elevation, near rivers in otherwise near-desert locations, and the plants were often rooted among boulders and growing up rock walls, along bridges, etc. In some cases I labeled slides with only the genus Clematis as host – this is simply due to my initial uncertainty about Clematis taxonomy. Clematis ligusticifolia is found from southern British Columbia and Alberta in the north to New Mexico in the south (Kershaw et al. 1998).”  I still have specimens from only Washington, Oregon, and Idaho.

Macrosiphum clum from Coffeepot Lake in eastern Washington.
Macrosiphum clum from Coffeepot Lake in eastern Washington.

Macrosiphum clydesmithi Robinson

This is one of my most familiar species of Macrosiphum, and one of 4 that feed on bracken fern, Pteridium aquilinum.  When in grad school in the early 1990s I worked out the taxonomy of all 4 species, including some mix-ups that had occurred in previous literature regarding identities of various fern-feeding Macrosiphum.

Macrosiphum clydesmithi fundatrix and her nymphs on Holodiscus in May in northern Idaho.
Macrosiphum clydesmithi fundatrix and her nymphs on Holodiscus in May in northern Idaho.

I published the results with a distinguished co-author, Jaroslav Holman, in 2000.

Back then I wrote about this species’ biology: “Robinson (1980) described M. clydesmithi from material collected in Utah and Oregon on bracken fern, Pteridium aquilinum (L.) Kuhn. At that time its life history was not known. Jensen et al. (1993) reported the heteroecious life cycle of this aphid, demonstrating that its primary hosts are species of Holodiscus (Rosaceae). It was found on Holodiscus discolor (Pursh) Maxim. in the lower elevations and higher latitudes of Oregon, and on Holodiscus dumosus (Hook.) Heller in the mountains and more southern parts of its range in Oregon. Holodiscus discolor is also the primary host of M. pteridis (see below, under that species). In areas of western Oregon where the two aphids both live, their phenologies differ markedly from one another in the autumn.

Macrosiphum pteridis remigrates to Holodiscus a few weeks earlier than does M. clydesmithi, which may not arrive on Holodiscus until most of its leaves have fallen in October. Mating then occurs in M. clydesmithi on the last remaining leaves in November. On Pteridium, M. clydesmithi is most often found in exposed sites such as open fields and roadsides. It is not tended by ants despite the fact that it sometimes co-occurs with M. rhamni, which is often ant-tended.”  In those days I studied this species on Holodiscus discolor ssp. discolor, which is a tall, upright shrub in and on the edge of coniferous forests.  Since then I have found that this aphid is one of the common species feeding on Holodiscus discolor ssp. dumosus in rocky outcrops on the edges of mountains and cliffs at moderate to very high elevations.

I now have material of this species from Washington, Oregon, California, Idaho, Colorado, and New Mexico.  It surely occurs in Arizona, Utah, etc. also, but I have not made a priority of collecting it since grad school.

Macrosiphum clydesmithi ovipara on Holodiscus in October in northern Idaho.
Macrosiphum clydesmithi ovipara on Holodiscus in October in northern Idaho.
Macrosiphum clydesmithi apterous vivipara on bracken fern in July in northern Idaho.
Macrosiphum clydesmithi apterous vivipara on bracken fern in July in northern Idaho.

Macrosiphum creelii Davis

This species is one of many that are very similar morphologically to M. euphorbiae, but that have distinct biology and ecology.  M. creelii specializes on legumes, particularly Vicia and Lathyrus.  It is often bigger than a typical M. euphorbiae, but not always.  During many years of pursuit, I eventually gathered material of all morphs from fundatrix to sexuales.  One of my favorite habitats to collect this species are the famous public beaches of Oregon.  Just at the edge of high-tide water line there often grows a large Vicia, and on that there is almost always the largest and most dramatic specimens of M. creelii.  In our local southern Oregon Ponderosa pine forests, M. creelii is uncommon but widespread on native Vicia and Lathyrus growing in the shade of conifers.

Macrosiphum creelii from the Fremont-Winema National Forest, a fork of Coffeepot Creek.

Macrosiphum dewsler Jensen

This is one of my two new species described in 2017.

Dewsler and Andy, April 2013.

It is yet another example of a species I’ve known about for a long time, but spent 12 years gathering adequate information and specimens to support a good description.  It is named after one of our deceased dogs, Dewey (also known as Dewsler, Mr. Dewsler, and Dewsldoerfer).

I wrote about this species: “This aphid
is monoecious holocyclic on its host Linum lewisii. As noted by Munz (1973), this plant occurs on dry slopes and ridges, mostly above 1,220 meters elevation in montane coniferous forests and pinyon-juniper woodlands. Personal observation makes it clear that this plant
begins its growing season early in the spring, and is highly drought tolerant through the summer and fall. The overwintering stage of the plant consists of
small above-ground shoots ready to grow immediately when conditions allow. The earliest collection I have made of M. dewsler was 3 June 2016 south of La Pine, Oregon. At this location, early June is very early spring in terms of plant growth, yet L. lewisii was in bloom and the aphid population thriving. I have not collected confirmed fundatrices of this aphid, the only possible specimens being these on 3 June 2016. I considered these specimens to most likely not be fundatrices, which means that egg hatch and population establishment must have happened remarkably early at this location. Aphid populations persist on the plant stems after petal fall and during fruiting, seemingly able to reproduce throughout the dry summer months. Alate viviparae are rare, possibly produced only during certain stages of the season or of plant growth, considering that my only alate specimens are from early in the growing season (early July in the mountains of northern New Mexico and early June in the mountains of southern Oregon). In life, this aphid is difficult to see on Linum plant stems, as individuals feed cryptically among the leaves.

Linum lewisii is naturally distributed throughout most of western North America (Munz 1973), and is closely related to the European Linum perenne L. (McDill et al. 2009). Although I have collected this aphid from only New Mexico, Oregon, and North Dakota (a sample from the latter state was secured while this manuscript was in review), it likely occurs where L. lewisii is found in similar habitats in Arizona, California, Nevada, Utah, Idaho, and Washington. McDill et al. (2009) analyzed the phylogeny of Linum and Linaceae, and found that L. lewisii is closely related to Linum species occurring in eastern Asia. Considering this and their estimated time of diversification of L. lewisii from its Eurasian relatives (3.8-3.3 million years ago), they thought it likely the ancestor of L. lewisii colonized North America via the Bering Land Bridge. It would  therefore be interesting to study relatives of L. lewisii in eastern Siberia to determine whether they may serve as host to M. dewsler or a close relative.”

Macrosiphum dewsler apterous vivipara from near Lakeview, OR.

Macrosiphum euphorbiae (Thomas)

In May of 2021 I was scrolling through this collection of blurbs about species of Macrosiphum when I noticed that I’d never posted information about the most widespread and well known species of this genus! It’s time to correct that oversight.

Often known as potato aphid, Macrosiphum euphorbiae is native to North America and has spread throughout most of the world. It is one of the most polyphagous aphids known, with many hundreds of documented hosts, and almost certainly there are many hundreds of additional plants that would be acceptable hosts if this aphid were given the chance.

The basic host plant biology in temperate climates is heteroecious, with overwintering on Rosa followed by migration to its many summer hosts, which can be trees, shrubs, and herbs (both monocots and dicots). Many aphid collectors (including myself) have found oviparae and eggs of this aphid on herbaceous hosts, but whether and to what extent it can successfully overwinter on plants other than Rosa is not known. Indoors or in warm climates this aphid can be anholocyclic.

My sense is that M. euphorbiae is likely native across most of North America, but in my experience its prevalence and diversity of appearance and habits is most extreme in the northwestern U.S. states and western Canadian provinces. In these regions there are times when most aphids found in natural systems, such as forests and meadows, are M. euphorbiae on its many secondary hosts. This can render any search for less common aphids a frustrating affair because M. euphorbiae seems to displace many other species.

As a pest of potato in the northwestern states where my experience is greatest, this aphid is an early colonizer, arriving on potato in places like eastern Oregon and Washington shortly after crop emergence (e.g. mid-late May to early June). It rarely stays in the crop beyond July 1, after which green peach aphid (Myzus persicae) takes over. Its ubiquity in natural systems across much of northern U.S.A., however, means that most potato crops are growing near native populations of potato aphid that could pose a threat, especially as virus vectors.

Taxonomically M. euphorbiae is challenging due to its lack of unusual features and because of its extreme variability in both color and morphology. A practical consideration for a taxonomist like myself is whether Macrosiphum specimens found on an unusual plant are typical M. euphorbiae, or M. euphorbiae that look different due to stresses imposed by climate, host plant, or microhabitat, or whether the specimens belong to a separate species. There are now many well-understood species of Macrosiphum around the world that look remarkably similar to M. euphorbiae but that have distinctive biology and life cycle with very slight morphological differences.

Below I present a range of photos of this species, showing all its morphs and some of the range of variation in appearance.

A fundatrix of Macrosiphum euphorbiae with a typical appearance and green color.
Another common color pattern for M. euphorbiae fundatrices and apterae in early spring.
A very dark fundatrix of M. euphorbiae that also shows shorter appendages than normal.
A summer apterous female of M. euphorbiae, showing the common green color.
Another common summertime color for apterae of M. euphorbiae.
A typical alate vivipara of M. euphorbiae.
Oviparae of M. euphorbiae, like many other species of Macrosiphum, are often red or orange.
A typical male of M. euphorbiae on Rosa in the fall season.

Macrosiphum garyreed Jensen

This is the second new species I published in 2017.  It is named after my undergraduate and graduate supervisor and mentor, Gary Reed.

Gary Reed in Hermiston, 2009.

Gary was an entomologist and superintendent of the Oregon State University Hermiston Agricultural Research and Extension Center in eastern Oregon.  He supported me through 8 years of my life, including paying for my Ph.D. education and supporting my work in systematics of aphids.

I wrote about this aphid: “This species is monoecious holocyclic on its host plant, Geum triflorum.  It was first discovered by Gary Reed in the early 1990s feeding among the developing achenes in the flower heads, but most of the season it feeds on the stems and leaves.  This plant has a similar over-wintering strategy as L. lewisii, discussed above, in that it overwinters with basal leaves intact, and ready to grow immediately in spring.  I have often observed flower heads extremely early in the spring, indicating that the plant must grow during warm spells in winter.  This produces a situation wherein fundatrices of M. garyreed are able to develop and deposit their offspring on the flower stems and buds of a strongly growing plant early in the season.  Although I have known about and collected this species since the early 1990s, it has been difficult to find the sexuales in the fall.  After blooming and seed drop, G. triflorum enters a more or less dormant vegetative state during late summer and fall during which M. garyreed is hard to detect and collect due to low population densities.  Until the fall of 2016 I had never collected this aphid late enough in the fall to find the sexuales.  My single collection site of sexuales was on a place called Winter Rim in southern Oregon in early October (8 October 2016).  As suggested by the place name, Winter Rim is a cold and windy high-elevation ridge.  When I collected sexuales of M. garyreed there, almost all other aphids were gone, long previously either migrated away or in hibernation as eggs.  Among the leaf litter were G. triflorum plants with both green and senescing leaves, the latter bearing many nymphs and adults of M. garyreed.

So far this aphid is known from only Oregon and Idaho in the U.S.A.  Geum triflorum occurs throughout much of western North America and across northern U.S.A. and Canada as far east as New York State (Hitchcock and Cronquist 1973).  I have looked for this aphid on its host across much of western North America, mostly without success, suggesting that it may have a restricted distribution in parts of Idaho, Oregon, and probably Washington and California (some of my collecting localities are very near state borders).  It is possible that the aphid’s distribution is related to a relatively narrow forest ecosystem(s) as compared to the broad distribution of G. triflorum.”

Macrosiphum garyreed in its pinkish color form, from the mountains of central Idaho.
Macrosiphum garyreed in its green form, from the mountains of central Idaho.

Macrosiphum gaurae (Williams)

Locally common, this aphid is probably a complex taxon composed of two to four species.  Out west in my area, this aphid feeds on Gaura and can be found in various habitats.  Its siphunculi are less reticulated apically than most Macrosiphum, and the tarsi look fat to me.  In Maine it is mostly found on native Oenothera, and the siphunculi look rather different but the tarsi are still fat.  In the south such as Florida and Texas, what might be called this species can be pink and have almost entirely dark siphunculi (much darker than in the photo below); these live on Oenothera and Gaura.  In the old days of aphid taxonomy, there’s no question that they would all be described as separate species due to their morphological disparity.  Today, after having many samples from across North America at my disposal (when I borrowed material from a couple collections), I still think there are likely 2 or more species, but can see why the current dogma is one of lumping: there IS a lot of variability across the continent but all specimens share some features like fat tarsi, convincing me of their relatedness.

From the lumper’s perspective, I have material of this ‘species’ from Oregon, Colorado, New Brunswick, and Texas.

Macrosiphum gaurae from eastern Oregon in May.
Macrosiphum gaurae from eastern Oregon in May.

Macrosiphum ginajo Jensen

The description of this species marked the 20th Macrosiphum I’ve named. I first found this aphid in 2008 on a hike with my sons in the Cascade Mountains of Washington State. It lives on sticky members of the plant genus Silene, and can be hard to find even in likely locations with appropriate host plants. I was lucky to live in southeastern Oregon for several years and to find some localities where M. ginajo is abundant, allowing me to collect all life stages and better understand its natural history. As I wrote about it in the paper:

Etymology. The species name is in honor of Gina Rone, who has supported hikes and camping outings aimed at finding this species for the past twelve years, waiting patiently in the forest as I search for Silene and its aphids. A geologist and forest soil scientist, Gina has helped me understand the ecology of this and many other aphids. For the purposes of the rules of nomenclature, the name should be considered an arbitrary combination of letters and treated as indeclinable.

Biology and Distribution. This aphid lives without host alternation on glandular–sticky members of Silene, especially Silene oregana S. Watson. The full host range of M. ginajo is not known because the author has not been able to make accurate species identifications of all sampled plants. One sample from Shoshone County, Idaho was
recorded as feeding on a Silene with pink flowers. This may have been Silene scouleri Hook., which is sticky like S. oregana, occurs across the known range of M. ginajo, and has pink flowers. Many stands of non–sticky Silene (probably Silene douglasii Hook.) have been searched for M. ginajo over the years, but without success. In the forests of Lake County, Oregon, where this aphid has been most thoroughly studied in the field, its S. oregana host plant occurs most commonly in association with white pine (Pinus monticola Douglas ex D. Don) or sugar pine (Pinus lambertiana Douglas) and often on soils associated with rhyolitic parent material.

So far, this aphid is known from Washington, Oregon, California, and Idaho. The range of S. oregana also includes parts of Montana, Wyoming, and Nevada (Hitchcock & Cronquist 1973), indicating that M. ginajo may occur in those states as well.”

Macrosiphum ginajo, probably a fundatrix, from Ochoco National Forest, Oregon.
Macrosiphum ginajo ovipara from Gearhart Mountain in southern Oregon.

Macrosiphum glawatz Jensen

I’ve been gathering field observations and specimens of this species off and on since the early 1990s. Being ant-tended, it is very unusual for its genus. I was finally able to gather enough material to publish it recently. As I wrote about it in the paper, “Etymology.—This species is named in honor of Claus and Helga Glawatz, parents of Gina Rone. Despite living in Germany and speaking little English, Claus and Helga have seen more of the United States than almost anyone, including much of the habitat of M. glawatz.

Macrosiphum glawatz apterous vivipara, June 2018 near Lakeview, Oregon.

Biology and distribution.—This aphid lives throughout the growing season on Potentilla gracilis in meadows and edges of dry forest. Much collecting effort over the years has not yet yielded any sexuales, and none of the apterae collected so far can be confidently labeled as fundatrices. Despite these facts, it is extremely likely that M. glawatz is monoecious holocyclic on P. gracilis.
Evidence supporting this idea are the collections of apterae of this species in early spring. At the time of these collections, such as 16 May or 30 May, P. gracilis in eastern Oregon is just entering
its pre-flowering growth stage and is in perfect condition for aphid reproduction. At the same time, shrubs and trees that might be host to an undiscovered primary host life stage are just beginning growth and would be very unlikely to support two spring generations of an aphid that then migrates to P. gracilis by early May. The lack of success in finding sexuales is related to two primary issues: the phenology and growth habit of P. gracilis and the nearly ubiquitous cattle grazing of relevant habitats.

Macrosiphum glawatz alate vivipara, June 2017, near Lakeview, Oregon.

The life cycle of P. gracilis is similar to the hosts of two other recently described Macrosiphum species from similar habitats, Macrosiphum dewsler Jensen on
Linum lewisii Pursh and Macrosiphum garyreed Jensen on Geum triflorum Pursh (Jensen 2017), in that it overwinters as a basal rosette and begins growing in early spring, flowers during the summer, and then survives the late summer drought as a basal rosette with very small leaves. It is likely that the sexuales of M. glawatz develop on these late summer rosette leaves but searching for them is challenging in part due to heavy cattle grazing and trampling that decimates M. glawatz habitat every summer. If a good site could be located that is free of grazing, M. glawatz could be followed from early spring through its presumed sexual stage in that site, but we have not been lucky enough to find such a place.

Macrosiphum glawatz is unusual among Macrosiphum and similar genera in that it is almost always tended by ants. The only other western North American Macrosiphum that is usually ant-tended is Macrosiphum rhamni (Clarke) when it is feeding on its secondary host, Pteridium aquilinum (L.) Kuhn. Only a few samples of the ants tending M. glawatz have been collected, but these all belong to the genus Formica L.

Macrosiphum glawatz is so far known only from Oregon and Washington east of the Cascade Mountains, but almost certainly occurs in nearby portions of California and Idaho.”

UPDATE June 2020: I was lucky to finally find the fundatrices of this species in our local Fremont-Winema National Forest. They were found on a robust specimen of Potentilla gracilis that was growing in a little-used gravel road at about 1,900 meters elevation at the top of a cool drainage. The fundatrices were on the developing stems near the base of the plant. The granules of soil around the base of the plant indicated the presence of the tending ants.

Macrosiphum glawatz from Union County, Oregon, June of 2012, showing the co-occurrence of red and green morphs.

Macrosiphum holodisci Jensen

I was the first to notice this aphid as new, and oddly it seemed to appear where it was not before in my normal aphid stomping grounds of McDonald State Forest in Oregon. I have collected aphids on Holodiscus very thoroughly for over 20 years now throughout western North America, and this species is extraordinarily uncommon. I have collected it now in only two locations, in Idaho and Oregon, and seen material from Washington and California. I published this species in 2000 and wrote about it, “Macrosiphum holodisci was originally discovered on its host, Holodiscus discolor (Pursh) Maxim. (Rosaceae), in the forests west of Corvallis, Oregon. Several specimens were collected during the fall of 1991, including some oviparae and males. Several oviparae were enclosed in the field in a thin cloth bag, and allowed to oviposit on the leaves and branches within the bag. The bag and its contents remained undisturbed throughout the winter, and the spring generations were reared within the bag until May, 1992. Interestingly, the oviparae laid their eggs on the leaves, twigs, buds, etc., yet the first instar nymphal fundatrices found each other upon hatching, and developed in tight clusters on the buds and young leaves through their second instar. This is in contrast to many other Macrosiphum, whose nymphal fundatrices tend to be more dispersed. The early instar fundatrix of this species is also unusual in that it has pairs of dark sclerites on the abdominal tergites, and because it is a striking yellow color, while the adult is white.”

Macrosiphum holodisci fundatrix from the Hayden, Idaho area.
Macrosiphum holodisci fundatrix from the Hayden, Idaho area.

Macrosiphum manitobense Robinson

This aphid is a source of embarrassment for me because it is one Macrosiphum species whose full host plant biology has eluded me for my whole aphid research career.  It was one of the first Macrosiphum species I studied in the field outside Corvallis, Oregon in McDonald State Forest.

Macrosiphum manitobense fundatrix from the shores of Moses Lake in central Washington.
Macrosiphum manitobense fundatrix from the shores of Moses Lake in central Washington.

It was common there in spring and fall on Cornus stolonifera.  It was obvious that a secondary host was utilized in the summer: all colonies in spring matured into alate viviparae and emigrated in April and May, and in  September and October alate viviparae and males returned to Cornus.  This was seen year after year.  Since that time I have collected this aphid elsewhere, in far flung places like Moses Lake, Washington, and Jemez Springs, New Mexico.  But, after 27 years of aphid collecting, I still have not turned up this aphid on its secondary host.  Its short cauda has lead me to speculate that it may utilize the lower parts or underground parts of a secondary host.  Even with this idea in mind, I have not found it anywhere but Cornus in spring and fall.  It is locally common, and obviously widespread, but in almost all places I look at Cornus stolonifera this aphid is not apparent.  The most obvious explanation for this patchy distribution is the aphid’s likely tie to a secondary host.  But what is that plant??

Blackman and Eastop imply that there may be two similar species on Cornus that might be confused under this name.  I agree that my material differs slightly from Robinson’s original description, but I think characters such as the unusually short cauda almost certainly indicate at least a close relationship between Robinson’s M. manitobense and mine. Recent study of the type of Macrosiphum potentillae (Oestlund) made me hypothesize in print (Jensen and Rorabaugh, 2020) that M. potentillae and M. manitobensis are closely related. The latter may in fact be the primary host form of the former.

I now have this species from Washington, Oregon, Utah, and New Mexico.

Macrosiphum manitobense second generation from near the ocean along the Nehalem River in Oregon.
Macrosiphum manitobense second generation from near the ocean along the Nehalem River in Oregon.

Macrosiphum mentzeliae Wilson

This interesting aphid feeds on the strange plant genus Mentzelia (Loazaceae), the species of which in my region are strangely sticky.

I think the sensation of stickiness is actually caused by a thick covering of trichomes (see photo).  I have only been collecting this aphid for a decade or so because it was only then that I learned how to recognize and find Mentzelia in my collecting.  It is an unusual plant in that it is most commonly found in dry places along roads in the northwestern U.S.A. — in such places I don’t spend much time collecting.  The most common host for this aphid in central Washington is the very showy Mentzelia laevicaulis, and I have collected it several times from a more diminutive species, probably M. albicaulis, and in New Mexico I’ve gotten it from a tall Mentzelia with big white flowers.  I have material of this species from Washington, Oregon, Idaho, Colorado, New Mexico, and Arizona.

Macrosiphum mentzeliae from central Washington. The brownish nymphs will develop into males.
Macrosiphum mentzeliae from central Washington. The brownish nymphs will develop into males.
Macrosiphum mentzeliae fundatrix from the Leslie Gulch area in eastern Oregon in March. This is a very early aphid for that region, in part because of the very warm and dry sites where M. laevicaulis grows.
Macrosiphum mentzeliae fundatrix from the Leslie Gulch area in eastern Oregon in March. This is a very early aphid for that region, in part because of the very warm and dry sites where M. laevicaulis grows.
Macrosiphum mentzeliae apterous vivipara from Coffeepot Lake in eastern Washington in August.
Macrosiphum mentzeliae apterous vivipara from Coffeepot Lake in eastern Washington in August.

Macrosiphum niwanistum (Hottes)

I still vividly remember the first time I found this aphid — it was in the Blue Mountains near the border of Washington and Oregon.  We’d camped in a cool drainage that doubled as a trailhead for a major cross-wilderness trail for hunters and backpackers.

Macrosiphum niwanistum apterous vivipara from the Blue Mountains.
Macrosiphum niwanistum apterous vivipara from the Blue Mountains.

The forest was alive with beasts, probably all deer, but in the dark of night, one never knows.  In the morning I arose to collect aphids as always, mostly right near camp among all the big fleshy wetland plants such as this aphid’s host, Mertensia (blue bells).  To my delight, the aphid was abundant and looked just like I read about in Hottes original description.  Most specimens live on the lower leaves of the plant, are covered in a light wax, and drop very readily from the plant when disturbed.  As I worked my way back toward the tent where Gina and Bumble still lounged, a man and a dog came down the trail!  The other end of the trail I knew to be about 17 km away, and the man and dog had no pack or water.  The dog arrived, and slumped immediately into a puddle in the trail at my feet.  The man carried a gun in a holster, and nothing else.  He explained that he was a trail maintenance contractor and had walked the full length of the trail that morning to scout how much work was needed to renovate the trail.  I offered him food and water, which he declined except for a couple gulps of water, he called his dog, and they headed back.  Ever since then I call him the hiking man — doing more hiking in the morning before breakfast than I want to do in a whole weekend.

This aphid turns out to be quite common and widespread.  I have it from Washington, Oregon, Idaho, Utah, and Colorado.

Macrosiphum niwanistum fundatrices and their nymphs from the mountains outside Boise, Idaho.
Macrosiphum niwanistum fundatrices and their nymphs from the mountains outside Boise, Idaho.

Macrosiphum olmsteadi Robinson

As I noted years ago on my Flickr page, Macrosiphum-like aphids I collect on Eurybia conspicua are probably best identified as Macrosiphum olmsteadi Robinson.  The other possibly correct species name is Illinoia (Masonaphis) magna (Hille Ris Lambers).  As far as I can tell from review of paratypes of M. olmsteadi and the original descriptions of both species, the main discrepancy between the two is number of setae on tarsal segments 1: 5 on I. magna and 3 on M. olmsteadi.  The two share distinctive characters such as the slightly clavate siphunculi, spinulose tarsi, setose tibiae and rostrum, etc.  Both are recorded from species of aster in the genus Eurybia.  Obviously this is another case of the muddled taxonomy of Illinoia vs. Macrosiphum that underlies our current aphid classification.

The aphids I identify as M. olmsteadi live on Eurybia conspicua in the interior mountains and foothills of Idaho and neighboring states and provinces.  This plant is interesting on its own — being a perennial herb that commonly grows on the forest floor and rarely blooms.  My interpretation of its biology is that it establishes in forests and grows only vegetatively until an opening in the forest canopy from tree fall allows adequate light for it to bloom.  This aphid is common on its host plants in shaded forest and also on the rare flowering specimens, feeding mostly on the undersides of leaves.  I have specimens from Idaho, Washington, Oregon, and Alberta.

Macrosiphum olmsteadi apterous vivipara from northern Idaho in June.
Macrosiphum olmsteadi apterous vivipara from northern Idaho in June.

Macrosiphum opportunisticum Jensen

This species I finally described recently after many years of collecting it occasionally in its mountain habitats. It was only after the paper came out in 2012 that I realized how long the species name is and that it hardly fits on a slide label and is a real bugger to write repeatedly.

As I wrote back then, “This species is monoecious holocyclic, but unusual in the breadth of its overwintering host range. It has been collected mostly in the mountainous areas of Oregon, Washington, Idaho, and western Montana, but also near sea level in the Seattle, Washington and Vancouver, British Columbia metro areas.
Host plants so far recorded for M. opportunisticum include: Altingiaceae – Liquidambar styraciflua L.; Caprifoliaceae – Symphoricarpos sp.; Celastraceae – Paxistima myrsinites (Pursh) Raf.; Ericaceae – Menziesia ferruginea Sm., Phyllodoce empetriformis (Sm.) D. Don, Phyllodoce sp., Rhododendron albiflorum Hook., Vaccinium membranaceum Douglas ex Torr., Vaccinium parvifolium Sm., Vaccinium scoparium Leiberg ex Coville, Vaccinium sp.; Rosaceae – Holodiscus discolor (Pursh) Maxim., Luetkea pectinata (Pursh) Kuntze, Sorbus sitchensis M. Roem., Sorbus sp., Spiraea thunbergii Sieb. ex Blume, Spiraea sp.

Macrosiphum opportunisticum alatoid nymph, showing the common pinkish color and light dusting of wax that occurs on nymphs.
Macrosiphum opportunisticum alatoid nymph, showing the common pinkish color and light dusting of wax that occurs on nymphs.

This host range, which includes a non-native tree (Liquidambar), is broader than most aphids, and might be viewed at first with skepticism. Observing M. opportunisticum in nature, however, puts this host range in perspective. This aphid normally lives in montane habitats dominated by shrubs of various kinds. Observations indicate that it is able to develop on many broadleaf shrubs available in its habitat. For example, in a harsh winter snow may linger well into July, preventing some shrubs from growing until mid-summer. Other shrubs, however, may be taller, or live in microclimates that are less affected by snow.

Macrosiphum opportunisticum alate vivipara.
Macrosiphum opportunisticum alate vivipara.

Over several seasons, when searching an area in the earliest parts of the growing season, whenever that occurs as dictated by snow pack and weather, M. opportunisticum can be found on any shrub in the list above (and perhaps others) that are in the best stage of development. The use of Liquidambar as a host in the Vancouver area supports the hypothesis that this aphid takes advantage of many available host plants. This aphid is widely dispersed on its host plants, with rarely more than one specimen on a leaf or twig. It drops readily from the plant when disturbed. An unusually large proportion of specimens in any given patch of infested host plant are alate or alatoid, and lone alates are frequently found throughout the short summers in its mountain habitat.”  Since this paper, I also found M. opportunisticum on Tsuga mertensiana (mountain hemlock) saplings along a mountain road in northern Idaho — a most unexpected host association.

I now have this species from British Columbia, Washington, Oregon, Idaho, Wyoming, and Utah.

Macrosiphum opportunisticum aptera from the Colockum Ridge of central Washington.
Macrosiphum opportunisticum aptera from the Colockum Ridge of central Washington.
Macrosiphum opportunisticum alate vivipara, the green color.
Macrosiphum opportunisticum alate vivipara, the green color.

Macrosiphum oregonense Jensen

This aphid has a special warm place in my heart, one of the oddest finds I made during my Ph.D. work. It lives on the giant and charismatic plant known as Lysichitum americanum (skunk cabbage). It is another species I published in 2000, and then I wrote, “This species is monoecious holocyclic on its host, Lysichitum americanum Hultén & St. John (Araceae). This plant is a semiaquatic herb with large broad leaves (some leaves reaching more than a meter in length), often growing in seeps, roadside ditches, and seasonally flooded areas. The particularly interesting thing about this aphid is that it can be found in the latter type of site. One collection in Benton County, Oregon was from a plant that is completely submerged during the winter. Whether the aphid overwinters in this site was never determined, but the possibility is most intriguing. Aphids feed on the undersurface of the leaves or among the bases of the leaves near the ground.”

This aphid is known from British Columbia, Washington, and Oregon.

Macrosiphum oregonense aptera from the Seattle area.
Macrosiphum oregonense aptera from the Seattle area.

Macrosiphum osmaroniae Wilson

This is one of the 4 species of bracken fern-feeding Macrosiphum aphids that I studied during my Ph.D. work in Oregon. I was the first to show host alternation in any of the fern feeding aphids, and it was even more unusual to study 4 related congeners utilizing the same host plant in the same general habitats. As I wrote about this back in 2000 (see reference above): “The heteroecious life cycle of this species is reported here for the first time. The primary host is Oemleria cerasiformis (= Osmaronia cerasiformis), and the secondary host is P. aquilinum. Egg hatch coincides with bud break in early to mid February in western Oregon. Fundatrices mature from mid March to early April. There is a second generation of apterous viviparae on the primary host, followed by alate migrants in late April and May. These migrants move to Pteridium, and produce small populations on this host. Throughout the summer this species is uncommon, a situation that leads to very few return migrants in the fall. Macrosiphum osmaroniae is often difficult to find on Oemleria in the fall, but in 1993 it was quite common in one area of McDonald State Forest. Gynoparae and males have not been found on Pteridium despite extensive searching. Gynoparae arrive on O. cerasiformis in September and early October, followed by males in late October and early November. Oviparae can be found in late October and November. Transfers of this aphid to a species of Dryopteris and to A. filix-femina were not successful. Late instar nymphs could complete development on these ferns, but did not reproduce.

Fundatrices feed among the leaves of the unfurling bud. They move to the undersides of leaves and to stems of actively growing shoots only after the bud is nearly unfurled, usually during the development of the second generation. Oemleria plants used as hosts are usually located in deep shade and near streams. The likely reason for this is that plants in this situation retain their leaves much longer into the autumn, and therefore are capable of supporting the autumn generations. When on Pteridium, M. osmaroniae lives on large plants growing in cool, shaded areas.

The developing fundatrices are often heavily parasitized by an aphidiine (Braconidae) wasp, Harkeria rufa Cameron. The adult of this wasp is orange-yellow throughout, slightly darker in the thorax. The later generations on Oemleria are also parasitized, but their numbers are rarely dramatically affected. Another aphidiine parasitoid found on this aphid in Washington was Aphidius polygonaphis (Fitch).

This species was observed to wave its body about in response to disturbance with a simultaneous release of siphuncular alarm pheromone. Individuals are also apt to drop from the plant when disturbed.”

I still have this species from only British Columbia, Washington, and Oregon.

Macrosiphum osmaroniae fundatrix in Olympia, Washington in April.
Macrosiphum osmaroniae fundatrix in Olympia, Washington in April.

Macrosiphum parvifolii Richards

This is a large, common aphid on Vaccinium species across northwestern North America.  It was originally collected on Vaccinium parvifolium (red huckleberry), a common species west of the Cascade Mountains, but I have since seen it on several other Vacciniums including V. scoparium, V. membranaceum, and V. ovalifolium.  I have also collected it on Menziesia ferruginea, another Ericaceae in the same habitats as infested Vaccinium species.  In late 2016 I am starting to suspect that this taxon is more complicated than originally thought, picking up some rather distinctive specimens on an unidentified Vaccinium in southern Oregon.  I suspect that more collecting and a closer look at the morphology and biology may elucidate at least one other similar species living on Ericaceae near the west coast.  I have material from Washington, Oregon, Idaho, and Montana.  Alate viviparae are exceedingly rare — I’ve seen only 3 of them in all these years (my first samples are from 1991).

Macrosiphum parvifolii fundatrix from north-central Washington in June.
Macrosiphum parvifolii fundatrix from north-central Washington in June.

Macrosiphum rhamni (Clarke)

I know I say it all the time, but this aphid is truly my favorite.  The reason?  This is the first aphid I conducted my own research on.  I was practically a pimply-faced kid when I started collecting this aphid, especially finding the beautiful oviparae on Rhamnus purshiana in the fall.

Macrosiphum rhamni oviparous female
Macrosiphum rhamni oviparous female

In those days this species was thought to be monoecious on that plant, which grows as a small tree in the forests of western North America.  Just as I began grad school in 1990 I was beginning to suspect that the story was more complex.  What was then considered to be Macrosiphum pteridis on bracken fern, Pteridium aquilinum, seemed to me to be morphologically identical to M. rhamni. So, further study ensued and in 1993 I published on the host alternation of this species, followed by clarification of the nomenclature of the similar fern-feeding Macrosiphum with Jaroslav Holman in 2000, when we wrote of M. rhamni, “The heteroecious life cycle of this species was reported by Jensen et al. (1993), who included evidence from morphology, phenology and host plant transfers. In western Oregon, egg hatch begins during mid February and probably continues through March, depending on location. Adult fundatrices can be found in the Corvallis area from mid-March to late April. There is usually a second generation of apterous viviparae, followed by a third generation made up almost entirely of alate viviparae that settle on Pteridium. In some locations, a small number of individuals remain on Rhamnus throughout the summer. Gynoparae and males mature during late September and early October, and after returning to Rhamnus, can be found until mid-November. Oviparae can be found abundantly from mid-October to late November.

One collection of oviparae together with males was made from Pteridium on the Oregon State University campus on 7.x.1990. It is not known if these reproduced successfully, or if any resulting fundatrices were able to survive on Pteridium. A single collection of two apterous viviparae was made from Polypodium hesperium Maxon in Seattle, Washington on by H.G. Walker.

Males and alate viviparae sometimes drop when disturbed, but apterous forms rarely do. This is the only species of Macrosiphum known to us that is tended by ants. It is frequently ant-tended on both hosts when populations are dense in the spring and fall. The first author has seen it tended by unidentified species of Formica L. and Camponotus Mayr.”

I have specimens from British Columbia, Washington, Oregon, Idaho, California, and New Mexico.

Macrosiphum rhamni oviparae from the Oregon coast in October. The red internal pigment is typical for oviparae and no other morph.
Macrosiphum rhamni oviparae from the Oregon coast in October. The red internal pigment is typical for oviparae and no other morph.

Macrosiphum rosae (L.)

Quite possibly, this is the most widely known aphid species in the Northern Hemisphere.

Macrosiphum rosae apterous vivipara from our garden in southern Idaho.
Macrosiphum rosae apterous vivipara from our garden in southern Idaho.

Almost everyone who has a garden, or knows somebody with a garden, or walks by other people’s gardens, knows about rose aphid, Macrosiphum rosae.  It is the aphid that occurs all across most of the world on cultivated roses.  What even some entomologists don’t know, however, is that this aphid also feeds on teasel (the genus Dipsacus), and sometimes other plants such as Potentilla, Epilobium, and Ilex (holly).  This aphid is native to Europe, where a close relative (Macrosiphum knautiae) lives throughout the year on Knautia — a close relative of Dipsacus.  In most places I’ve lived, M. rosae lives without a sexual cycle throughout the year on roses, or migrates in from places where this is possible.  That said, I do have two fundatrices in my collection, indicating a sexual cycle sometimes occurs in northwestern U.S.A.

Macrosiphum rosae alate vivipara colonizing our rose from elsewhere in April. The green nymphs are Wahlgreniella that overwinter as eggs on the same plant.
Macrosiphum rosae alate vivipara colonizing our rose from elsewhere in April. The green nymphs are Wahlgreniella that overwinter as eggs on the same plant.
The head and thorax of a feeding alate Macrosiphum rosae.
The head and thorax of a feeding alate Macrosiphum rosae.

Macrosiphum rudbeckiarum (Cockerell)

I still remember the first time I found this species after many years of looking on Rudbeckia (its host) everywhere I went. It was in northern Idaho along a meandering stream that at intervals broke out into wide marshy ponds. Moose were nearby, and I found this aphid on the lower leaves of tall Rudbeckia plants adjacent to a moose trail that crossed the stream. Just as described by earlier authors, this aphid lives on the lower leaves of its host, and appears to be mostly restricted to the more interior mountains of Idaho and adjoining states.

Like so many species of Macrosiphum in North America, it is generally similar to M. euphorbiae, but in life appears to be more long bodied and bigger in general, and finding it on the lower leaves in cool shaded locations is also a good hint. In one location in Utah, in the hills above Salt Lake City in the fall, I was collecting Macrosiphum on the leaves of both Rudbeckia and Agastache in the same location as was M. euphorbiae. After mounting, I found just how similar these species are. It seems to me that Macrosiphum has recently diversified in the West, leaving biologically distinct species very similar in morphology.

M rudbeckiarum Clearwater vii 2010 2
Macrosiphum rudbeckiarum alate vivipara from northern Idaho.
Macrosiphum rudbeckiarum in northern Idaho, the apterous vivipara.
Macrosiphum rudbeckiarum in northern Idaho, the apterous vivipara.

Macrosiphum schimmelum Jensen

I recently described this species after many years of collecting it and getting to know its biology in the field.  In my 2015 paper I wrote, “This species has been found almost everywhere that I have seen its host, L. utahensis. Fundatrices live singly on the undersides of leaves, and are dusted with highly variable amounts wax, as are their offspring. Recent presence of the aphid can often be detected by the waxy residue left on the leaf surfaces. Aphids congregate on flowers and fruits when they become available, until fruits are fully mature. Alatae seem to be produced primarily during fruiting of the host plant. In any given forest location this aphid is usually widespread but in low numbers on each host shrub, living both in heavily shaded areas and exposed slopes and clearings. Lonicera utahensis is known from southern British Columbia and Alberta in the north to Wyoming and Utah in the south (Kershaw et al. 1998).

Fundatrices have been collected in May and well into July; the latter dates are not understood, considering the fundatrices found in May were from a similar habitat and elevation. It is possible that egg hatch occurs over a protracted period in this species, perhaps due to its montane habitat, and it is also possible that the fundatrices collected in July were simply long-lived and intermingled with their daughters and granddaughters on the plants.”

I still have material from British Columbia, Washington, Oregon, and Idaho.

Macrosiphum schimmelum fundatrix from the Blue Mountains of Oregon in early July.
Macrosiphum schimmelum fundatrix from the Blue Mountains of Oregon in early July.

Macrosiphum stanleyi Wilson

This common species is one of the biggest and spindliest aphids I know.  It feeds on elderberries, genus Sambucus (Caprifoliaceae), and is found from the Rocky Mountains to the ocean coast.  I’ve seen it in habitats from dry steep slopes of mountains in New Mexico to the deepest darkest understory of western Oregon rain forests.

I have material of this aphid from British Columbia, Washington, Oregon, and Idaho.

Macrosiphum stanleyi apterous vivipara from Tillamook County, Oregon, along the Nehalem River.

Macrosiphum thermopsaphis Knowlton

This species name is officially considered a synonym of M. zionense, but I disagree with this assessment. I cover the details of my opinion above under M. albifrons, to which this species is very similar in life. Originally described from Thermopsis in central Colorado, I have samples on Thermopsis from Colorado, Utah, and New Mexico. These include all morphs: fundatrix, apterous and alate females, oviparae, and alate males. Because these samples are easily separated from M. albifrons and M. zionense (sometimes collected together with the latter species on Thermopsis), I think it best to highlight this fact by using Knowlton’s species name.

Macrosiphum tolmiea (Essig)

I worked on the field biology of this species for several years in grad school, it being one of the aphids I searched for during my weekly trips to McDonald State Forest outside of Corvallis.  During that time and in that location, it seemed to be anholocyclic on its hosts in the Saxifragaceae (e.g. Tolmiea, Tellima, and Mitella), almost completely disappearing during the summer and appearing seemingly from nowhere in the spring.  Since that time I was lucky enough to find M. tolmiea in the fundatrix stage on the lower slopes of Mt. Baker in Washington, confirming that at least sometimes it is holocyclic.  I still have material only from British Columbia, Washington, and Oregon in the wet forests west of the Cascade Mountains.

Macrosiphum tolmiea from Tillamook County, Oregon, near the Nehalem River.

Macrosiphum tonantzin Rebeca Peña-Martinez, Ana Lilia Muñoz-Viveros,
& Jensen

This is an aphid I had the pleasure to work on with colleagues I’ve never met in Mexico (and California!).  They found M. tonantzin living on the non-native tree Pittosporum undulatum in Mexico City.  In the paper describing this species, we wrote, “So far this aphid is only known from a single site in Xochimilco area of southern Mexico City.  Here, it lives throughout the year on the growing tips of ornamental trees of P. undulatum. The second and third authors have observed that P. undulatum is not a common plant in Mexico City, and the site where they find M. tonantzin is the only site they have seen this plant.  Further, they note that Pittosporum tobira (Thunb.) W.T. Aiton is common in Mexico City but despite extensive searching they have not been able to find M. tonantzin feeding on it. The production of alate males starting in December, in the absence of oviparae, suggests that this aphid’s native biology may be heteroecious. The species is, however, so far not known from any native plants. … The species is meant to honor the Nahuatl name for an Aztec mother goddess.” My hypothesis presented in this paper was that M. tonantzin is a species native to Mexico that has successfully acquired P. undulatum as host. An alternative hypothesis, that this aphid is native to Australia or another place where Pittosporum grows naturally, cannot be entirely discounted, however.

Macrosiphum tonantzin from Mexico City. Photo by: Rebeca Peña-Martinez

Macrosiphum tuberculaceps (Essig)

This is another species I really enjoyed working on. Essig did a great job of describing M. tuberculaceps, but the samples he worked from were not associated with a known host plant. I covered this species in my 2000 paper, as follows, “The description and figures by Essig (1942) are adequate. At the time of his description, the actual host plant of this species was not known, which probably led to its never being identified since. It should be noted that the dorsal head tubercles for which Essig named this species are not the usual condition for the species. The single available alate vivipara has large spinal tubercles on the head, but these are in the normal position, not as drawn by Essig.” And, “This species is monoecious holocyclic on its only known host plant, Achlys triphylla (Smith) DC. (Berberidaceae). In the Corvallis area, egg hatch occurs in March. Fundatrices mature in April. Alatae are rarely produced. Oviparae and the rarer alate males can be found in October and November. Populations are dispersed, with few aphids on any given plant. The aphid is rare and difficult to find at times. Adults are apt to drop when plants are disturbed.”

I know this species from British Columbia, Washington, and Oregon.

Macrosiphum tuberculaceps aptera from the Cascade Range of Washington.
Macrosiphum tuberculaceps aptera from the Cascade Range of Washington.

Macrosiphum valerianae (Clarke)

In 2012 I published a paper that included what i knew about this interesting aphid:

Jensen, A.S. 2012. Macrosiphum (Hemiptera: Aphididae) Update: One New Species, One Synonymy, and Life Cycle Notes. Proceedings of the Entomological Society of Washington 114: 205-216.

In that paper I wrote, “Host plants I have witnessed this aphid reproducing on in nature include: Apiaceae – Lomatium sp.; Asteraceae – Taraxacum officinale; Brassicaceae – Arabis sp.; Melanthiaceae – Zigadenus sp.; Onagraceae – Epilobium angustifolium L.; Rosaceae – Geum macrophyllum, Geum rivale, Geum triflorum Pursh, Potentilla sp., Rosa acicularis; Scrophulariaceae – Pedicularis groenlandica, Penstemon sp.; Valerianaceae – Valeriana sp. Additional hosts recorded in the literature include: Asparagaceae – Camassia scilloides (Raf.) Cory; Asteraceae – Hymenoxys hoopesii (A. Gray) Bierner, Rudbeckia sp.

This aphid is monoecious holocyclic, probably with several overwintering hosts. On 29 May 2010 at about 1000 meters elevation, many Zigadenus plants were supporting colonies of M. valerianae that had been established by alate viviparae. A few colonies were found that were older and had a single fundatrix and an occasional apterous vivipara. It was clear in that site and time that fundatrices were quite old, and that most of their first generation offspring had been alate.

Macrosiphum valerianae is known from most U.S. states and Canadian provinces in the western half of North America. It is most often found in mountains and foothills.”

In 2020 I published my finding that Macrosiphum potentillicaulis Miller is a junior synonym of M. valerianae. It was really nice to finally resolve that question, originally brought up during my work with Macrosiphum impatientis in the 1990s.

I now have two slide boxes devoted to this species, having collected it from British Columbia, Quebec, Washington, Oregon, Idaho, Colorado, Wyoming, and New Mexico.  I was lucky enough to get some good photos over the years as well.

Macrosiphum valerianae fundatrix collected on Rosa near Lakeview, Oregon.
Macrosiphum valerianae apterous vivipara feeding on Camassia in central Washington.
Macrosiphum valerianae alate vivipara feeding on Camassia in central Washington.

Macrosiphum vancouveriae Jensen

Another fondly remembered aphid, this is also one I was the first to discover during the early 1990s.  It is striking that this species and M. tuberculaceps often live in the same forests, on related and peculiar herbs in the Berberidaceae.  In the McDonald State Forest where I studied aphids for grad school, this aphid was fairly easy to find, but outside of that habitat I have searched hundreds or thousands of its hosts, Vancouveria hexandra, and found it only a few additional sites.  Any time a species I’ve described is so hard to re-collect after the description is published, I start to wonder whether the whole thing was my imagination.  This feeling has been particularly acute with M. vancouveriae until last September when I finally found it again on the Rogue-Umpqua Divide in Jackson County, Oregon.  I still have material only from Oregon.

Macrosiphum vancouveriae apterous vivipara from the Rogue-Umpqua Divide in Jackson County, Oregon.

Macrosiphum violae Jensen

Another obscure and uncommon species I discovered in McDonald State Forest in Oregon during my Ph.D. thesis work. I published on it in 2000, commenting as follows, “This species is monoecious holocyclic on its host Viola glabella Nutt. Egg hatch in the Corvallis area occurs as the leaves are unfolding in March. Fundatrices mature by mid-April. Aphid numbers reach their peak during flowering in late-emerging plants and fruiting in earlier-emerging plants. Apterae reproduce slowly throughout the summer, rarely producing alatae. Sexuales are produced in September and October.

Attempts to transfer this species to Vancouveria hexandra and Viola sempervirens Greene were both unsuccessful. The transfer to V. sempervirens was done in the laboratory, where after one day the transferred fundatrix left the plant, and its single deposited nymph was dead. Transfers to V. hexandra were attempted in the field, where adult females survived for several days, but did not settle or reproduce.”

Like a number of aphids that live on herbs in the forest, this species is found only in microhabitats where the host plant is able to remain vegetative throughout the summer into fall. In many sites Viola glabella dies back well before fall due to dry soil.

I still have only found this aphid in Oregon and Washington.

Macrosiphum violae aptera from the Cascade Range in Washington.
Macrosiphum violae aptera from the Cascade Range in Washington.

Macrosiphum walkeri Robinson

This is one of the fern-feeding species that I studied extensively for my 2000 paper with Jaroslav Holman.  At the time I believed it to be anholocyclic with a wide host range on various ferns.  Since that time I published on the heteroecious life cycle of this species in the southwestern U.S., where it uses Holodiscus (Rosaceae) as primary host. In that paper I wrote the following about this species.

“The biology and complex history of M. walkeri, and the name previously incorrectly used for many samples of aphids from miscellaneous ferns in western North America, Macrosiphum adianti (Oestlund), was covered in detail by Jensen and Holman (2000). At the time there was no proof of a holocycle for this species and in fact it was definitively shown to be anholocyclic in western Oregon on the common forest ferns Polypodium glycyrrhiza D.C. Eaton and Polystichum munitum (Kaulf.) Presl. Jensen and Holman (2000) noted that some samples identified as M. clydesmithi in dry areas such as eastern Oregon and Washington, and New Mexico and Arizona did not conform well with most M. clydesmithi, having thicker siphunculi, longer setae, and sometimes secondary rhinaria on ANT IV in alatae. Over the years I gradually accumulated samples from New Mexico (during annual autumn vacations), collecting on Holodiscus, that looked like migrants of M. walkeri. This suggested that there were heteroecious holocyclic populations of M. walkeri outside of the warm and wet forests west of the Cascade Mountains and Coast Range. This made sense considering a few samples of fern aphids from cold high–elevation locations where anholocycly is unlikely. This mystery was definitively settled in 2019 when I found a dense infestation of M. walkeri on a tall H. discolor shrub adjacent to the Trampas Creek Trail in the Carson National Forest of New Mexico. The leaves of this plant were coated in aphids: alatae, oviparae, and males (Fig. 35). This find prompted a vigorous search for aphids on all ferns living nearby, aiming to confirm that aphids were emigrating from one of them. On a steep slope adjacent to a stream near the trail, from an unidentified small fern, I was able to recover a single apterous vivipara, three males, and numerous nymphs. Later microscopic inspection showed that the samples from Holodiscus and the unidentified fern were conspecific and fit the concept of M. walkeri. It was later discovered that some specimens collected from Holodiscus (uncertain species due to intermediate leaf size) from the San Isabel National Forest near Maysville, Colorado were also M. walkeri.”

Macrosiphum walkeri apterous vivipara on Polypodium near the Bonneville Dam in Oregon.
Macrosiphum walkeri on Holodiscus in New Mexico.

Macrosiphum willamettense Jensen

I discovered this species during my Ph.D. thesis work, originally in the wet flat land of the central Willamette Valley of Oregon, hence the species name. It was published in 2000 (see my list of publications above).

This is what I wrote about the species back then, “This species is monoecious holocyclic on its host Spiraea douglasii Hook. It is often difficult to find, even on plants that are infested. The aphids seem to prefer the freshest growth of the plants. This fresh growth is often on the water sprouts around the edges of the plant patch. The plant is an inhabitant of wet places like swamps and wet meadows, but in practice the commonest place to see it is in roadside hedgerows. Macrosiphum willamettense sometimes lives together on the same plants with Illinoia spiraeae (MacGillivray).”

Since the original description I have found this aphid in many other places, and its known range now includes British Columbia, Washington, Oregon, Idaho, and Montana.

Macrosiphum willamettense apterae and nymphs from central Washington.
Macrosiphum willamettense apterae and nymphs from central Washington.

Macrosiphum wilsoni Jensen

I named this species after one of my heros of aphid taxonomy, H.F. Wilson, who worked in Corvallis, Oregon in the early 20th century. I described this species in 2000 and since have had a little remorse about the decision — I am not sure how many species we have in northwestern North America on the big forest lilies. It seemed clear during my Ph.D. work that there were two, M. wilsoni, and Macrosiphum insularis Pergande. However, several samples I have seen from Idaho and British Columbia have made me doubt my judgement back then. Anyhow, maybe more field work will resolve the issue.

Back in 2000 I wrote about M. wilsoni, “This species has a simple monoecious holocyclic life cycle on species of Disporum. It has been collected on Disporum hookeri (Torr.) Nicholson and Disporum smithii (Hook.) Piper. Both of these plants are perennial, and remain vegetative throughout the summer months. Alatae migrate readily from their home plant upon emergence. The species is often difficult to find in McDonald State Forest because it is not faithful to particular patches of plants year to year, as are some other species described above.”

I now have identified this species from Oregon, Washington, British Columbia, and Idaho.

Macrosiphum wilsoni aptera from the forests near Hayden, Idaho.
Macrosiphum wilsoni aptera from the forests near Hayden, Idaho.

Macrosiphum zionense Knowlton

This is a really fabulous aphid, probably a close relative of M. albifrons. Although the specimens in the photos are yellow and green, M. zionense is often a beautiful orange color, with striking dark siphunculi and tibiae. It feeds on a plant called Thermopsis (‘golden pea’) in the mountains of the interior west of North America.

Throughout most of the season the aphids are found on the upper stems of the plant, but later in fall as the plants decline and the aphids transition to the oviparous female and male stages, they are found on the lower stems of the plants, just above the soil level, or on stems of plants that have fallen over during the growing season.

For additional discussion of this species, see above under M. albifrons.

I have specimens from Oregon, Idaho, Colorado, and Utah.

Macrosiphum zionense fundatrix, the golden color form.
Macrosiphum zionense fundatrix, the golden color form.
Macrosiphum zionense aptera, the green color form (obviously) -- it can also come in bright orange.
Macrosiphum zionense aptera, the green color form (obviously) — it can also come in bright orange.