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Genus PemphigusPoplar gall aphidsOn this page: Pemphigus betae bursarius gairi immunis longicornus obesinymphae populi populicaulis populiglobuli populinigrae populiramulorum populitransversus protospirae spyrothecae trehernei vesicariusGenus Pemphigus [Pemphigini]Pemphigus are small to medium-sized yellowish-green or greyish-green aphids which cause galls on the leaves, petioles or branches of their primary host. The fundatrices have spinal, pleural and marginal wax glands on most body segments. The winged viviparous females that develop in the galls have a black head and thorax and have the abdomen dusted in wax. The primary host of Pemphigus species is Populus (poplar), where they are not attended by ants. Their secondary hosts include Asteraceae and Apiaceae, whilst some Pemphigus species remain on one host all year. Pemphigus betae (Sugar-beet root aphid) North AmericaIn the spring, fundatrix nymphs of Pemphigus betae emerge from overwintered eggs laid beneath the bark of poplar trees, usually narrowleaf cottonwood (Populus angustifolia) or balsam poplar (Populus balsamifera). They colonize leaves just as the buds begin to open. A gall is initiated along the midvein of an expanding leaf by the fundatrix probing the leaf tissue with her stylet moving between parenchyma cells to reach the phloem cells. This creates a leaf-fold gall on or adjacent to the midrib, on the leaf underside. These galls may be yellowish-green, or green, strongly tinged with red (see first two pictures below). The gall-opening can be either on the upper side of the leaf, or underneath along the mid-rib. The fundatrix parthenogenetically and viviparously produces a generation of several hundred offspring. These develop to alatae which migrate from the primary to the secondary host (sugar beet roots). First and third images copyright Pretorius (2016) under a Creative Commons License. The head and thorax of the emigrant alate of Pemphigus betae (see third picture above) is black, and the abdomen is dull green to yellow with powdery wax; appendages are dusky. Secondary rhinaria are distributed 5-11 on antennal segment III, 1-4 on segment 1-4, and 0-3 on segment V. The rostrum hardly reaches the second pair of coxae, with the apical rostral segment less than 0.55 times the second hind tarsal segment. The wings are somewhat smoky.
Image copyright Pretorius (2016) under a Creative Commons License. Apterae of Pemphigus betae on the secondary host (see picture above) are yellowish, sometimes thickly covered with wax, so they appear whitish. The last three or four segments of the abdomen secrete long threads of flocculent wax. Wax pore-plates are absent from the head and typically also from thorax and margins of the abdomen. The body length of these adult apterae is 1.9-2.4 mm. Pemphigus betae makes pouch-shaped galls on its primary hosts, mainly narrowleaf cottonwood (Populus angustifolia) and balsam poplar (Populus balsamifera), in spring. Alatae leave galls in late June-early August to colonise roots of their secondary hosts sugar beet (Beta vulgaris), as well as other members of the Amaranthaceae such as fat hen (Chenopodium album). Ant attendance for this species has not been reported, and they appear to deal with the problem of honeydew 'pollution' by coating their honeydew droplets with wax. The species is widely distributed in North America, both as holocyclic populations and as anholocyclic populations overwintering on the secondary host. Pemphigus betae, or a species very similar to it, has also been reported in Europe.
In spring, Pemphigus bursarius form yellowish or reddish pouch-shaped galls (see first picture below) on the petioles of the leaves of their primary host, poplar (mainly Populus nigra). There may be more than one gall per petiole and the leaf lamina may curl and yellow. Inside the gall the developing Pemphigus bursarius fundatrix is green with brown head and legs, wax covered and has no siphunculi. The 4-segmented antennae of the mature fundatrix are about 0.12-0.15 times the length of the body. The fundatrix then produces large numbers of alate offspring (see second picture below) which leave the gall in late May.
The winged viviparae (see micrographs below) that emerge from these galls are greyish-green or greyish-brown with small siphuncular pores and are lightly covered with wax powder. There is brown shadowing around the wing veins. Their antennae are 0.33-0.4 times the length of the body and have a distinct terminal process. When the antennae are 6-segmented, the third antennal segment is 2.09-2.65 times longer than the fourth antennal segment (cf. Pemphigus gairi where the third antennal segment is 1.53-2.00 times longer than the fourth antennal segment). The alate viviparae colonise the roots of Asteraceae, especially lettuce (Lactuca). In July the colonies on the roots only produce apterous forms, but in August winged sexuparae begin appearing on lettuce. The third picture above shows a developing winged sexupara living on the roots of lettuce. Pemphigus bursarius host alternates between poplar and members of the daisy family (Asteraceae), especially lettuce. In summer they live on the roots of the secondary host where they can be a serious pest of lettuce. Its distribution is almost cosmopolitan being found in Europe, western and central Asia, the Americas, northern and southern Africa and (possibly) Australia and New Zealand.
In spring Pemphigus phenax and Pemphigus gairiform yellowish or
reddish elongate pouch-shaped galls on black poplar (Populus nigra) (see first picture below). The galls are usually more or less in the middle of a leaf, and are on or near the midrib. The slit-like opening on the underside extends over the entire length of the gall. (cf. Pemphigus populinigrae which induce broader pouch-shaped galls with the opening extending over part of the gall).
Given the features above (colour and thickness) the gall below would appear to be Pemphigus phenax. Note however, that some authorities (e.g. Blackman) believe that the galls of these two species are too similar to differentiate. Inside the gall the developing Pemphigus fundatrix is dull green or greyish green, and is covered with wax. The 4-segmented antennae are about 0.12-0.15 times the body length.
The offspring of the fundatrix develop into winged viviparae (see second picture above) that emerge from these galls in summer through an opening on the underside of the leaf. They have a black head and pterothorax, small siphunculi and a rather elongate greenish wax-dusted abdomen.
Pemphigus gairi host alternates between poplar and fool's parsley (Aethusa cynapium). In summer they live on the roots of the secondary host. Pemphigus gairi has been found in England, Czech Republic and Ukraine, but it probably occurs widely in Europe.
Pemphigus phenax host alternates between poplar and the roots of wild and cultivated carrots (Daucus carota). Apterae on carrot roots are pale lemon-yellow to yellowish white with white wax. Colonies may also persist parthenogenetically on carrots that remain in the ground through the winter. Pemphigus phenax is found in northern Europe (England, Denmark, France, Germany, Netherlands, Sweden), and is also recorded from Turkey and west Siberia.
The galls of Pemphigus immunis can be found on poplar trees. In shape and texture they are walnut-like, thick-walled, green-brown or red (see first two pictures below) and quite large, 2.5-4.0 cm in diameter. The gall is strongly curved so the broad apical opening lies at the base of the gall (see base of red gall in second picture below). The glaucous-green fundatrix produces large numbers of green waxy offspring which all develop to alatae (see third picture below).
The alatae of Pemphigus immunis usually have no secondary rhinaria on the base of antennal segment VI (cf. Pemphigus borealis which usually has two or more secondary rhinaria on the base of antennal segment VI). The primary rhinarium on antennal segment V is very large (more than half encircling the segment) and often has small round islands. There are 7-9 secondary rhinaria on segment III, 2-4 on segment IV, 0-1 on segment V, and none on the base of VI. First and third images above copyright Marko Šćiban, all rights reserved. The alatae migrate to the secondary host (Euphorbia) and found colonies on the roots. The resultant apterae are coated with copious amounts of wax.
The primary host of Pemphigus immunis is poplar (Populus), especially black poplar (Populus nigra) and Euphrates poplar (Populus euphratica). Alatae emerge from the gall from April to August and host alternate to the roots of Euphorbia species such as madwoman's milk (Euphorbia helioscopia) and petty spurge (Euphorbia peplus). Pemphigus immunis is found in much of Europe (but not Britain, Denmark, Norway, Sweden, Finland, Estonia, Latvia or Lithuania), north Africa, south-west and central Asia, Pakistan, north-west India and China.
The galls of Pemphigus longicornus (see first picture below) are induced by the fundatrix on the upper side of the leaves of Eastern cottonwood trees (Populus deltoides ssp. deltoides), without involvement of the leaf petiole (cf. most other Pemphigus galls on this host which are on the stem or involve the leaf petiole). The galls are similar in form to a rooster's crest, resembling those of Colopha graminis on elm, although they are less notched at the top, and less ribbed on the sides. The galls have thin walls, and are slightly constricted where attached to the leaf. They are usually green, and measure about 16 mm in length, 13 mm in height, and only about 5 mm thick. The gall has a narrow slit opening on the underside of the leaf (see second picture below), where some of the wax-coated honeydew can be ejected, and later where the emigrant alatae depart from the gall.
The gall is induced by the fundatrix of Pemphigus longicornus (not pictured). The fundatrix is pale, yellowish white, and covered with wax. Wax pore plates are arranged as normal for the genus, and are variable in size. The largest are those at the margin, and on the posterior segments of the abdomen. The secondary rhinaria at the distal end of antennal segment III & IV are oval, and are fringed with cilia. Her offspring, the fundatrigeniae, (see thiord picture below of immature and mature alatae) are greenish yellow, and all develop to alatae.
First two images copyright Beth Burrous under a creative common licence; The migrant alatae (see two wax-covered alatae in third picture above) have the abdomen a creamy yellow, with the thorax and head dark, almost black, with a bluish tinge. The legs and antennae are dusky. The antennae are long, about 0.5 times body length, reaching to the posterior margin of the metathorax. Siphunculi are usually present, but are weakly developed. The base of antennal segment III is usually slightly swollen for a short distance. Secondary rhinaria, which encircle or nearly encircle the antennal segments, are distributed 19-27 on segment III, 6-8 on segment IV, 9-12 on segment V and 8-l2 on segment VI (cf. Pempigus populicaulis, which has rhinaria distributed 8-13 on III, 2-5 on IV, 2-5 on V, and 3-7 on VI). Body length of Pemphigus longicornus migrant alatae is 1.7-2.1 mm. Pemphigus longicornus host alternates from cockscomb-shaped galls on upper sides of leaves of the primary host, Eastern cottonwood (Populus deltoides), to an unknown secondary host. This migration occurs in May-June. In the autumn, sexuparae migrate back to Populus where they deposit the sexuales. Pemphigus longicornus is quite widely distributed in eastern and southern USA, but is generally regarded as a rather rare species.
The Pemphigus obesinymphae life cycle is rather different from other Pemphigus species. Instead of overwintering as eggs on the primary host (poplar), they overwinter as viviparae on the secondary host (roots of Brassicaceae). In spring these populations produce sexuparae, which fly to Populus after the initial leaf flush. The sexuparae on poplar produce the sexuales, that mate in the usual manner on the bark, and then lay eggs on the primary host, albeit rather later in the year than the closely related Pemphigus populitransversus. The eggs hatch rapidly, with no period of diapause, to give the fundatrices. These feed on the petioles of late-flushing leaves of Populus fremontii and Populus deltoides, inducing gall formation.
Pemphigus obesinymphae galls (see first picture below) are usually more-or-less spherical, and are close to the leaf blade, though do not incorporate the leaf midrib (cf. Pemphigus populitranversus, which usually has rather more elongate galls, positioned about mid-way along the petiole). When mature the galls are 8-16 mm in diameter, with the lips of the transverse slit sometimes bulging outwards, and a circular ostiole (=small opening) about 1.2 mm in diameter somewhere along the slit. The ostiole allows defenders to enter and exit the gall. Only two generations occur in the galls: the fundatrix, which is apterous, and her offspring, the fundatrigeniae, all of which are winged.
The adult fundatrix of Pemphigus obesinymphae (see large brown, white-tufted, aphid in second picture above) has 4-segmented antennae. The apical rostral segment is without secondary hairs. The shape and distribution of wax plates is as usual in Pemphigus species. The eighth tergite has 10-19 hairs. The first-instar progeny of the fundatrix in the gall are heavily sclerotized with well-developed forelegs. These adaptations enable them to attack predators. The 2nd and 3rd-instar progeny are usually much-swollen (hence the names 'obesinymphae' and 'cherubic'), and resemble wingless adults. Why they are so swollen is unknown. Alatae do not leave the galls till August-October, migrating like Pemphigus populitransversus to cruciferous hosts on which overwintering occurs.
First two images copyright James Bailey, third image copyright Millie Basden; The alate Pemphigus obesinymphae fundatrigenia (see two alatae in third picture above) has 6-segmented antennae. Antennal segment III is shorter than segments IV + V together and the rhinarium of segment V is rather large and approximately square. Antennal segment III has 3-6 secondary rhinaria, with 0-1 rhinaria on IV and V. The secondary rhinaria are normal in type, extending at most round a fraction more than half the circumference of segment III. The apical rostral segment is about as long as the second hind tarsal segment (HTII). Separation from Pemphigus populitranversus requires examination of the embryos within the emigrant alatae. Embryos of Pemphigus obesinymphae in the emigrant alatae have the tip of their rostrum extending beyond the first segment of the fore-tarsi (cf. embryos of Pemphigus populitranversus in the emigrant alatae, in which the tip of the rostrum does not extend beyond the first segment of the fore-tarsi). There are small oval to transversely elongate spinal wax plates on abdominal tergites I-VI, and a large elongate one on VIII, but plates on most posterior tergites are reduced in size. Siphunculi are ringlike, with only half of the "ring" sclerotized.
Pemphigus obesinymphae host alternates from cottonwood (Populus), its primary host, to the roots of Brassicaceae, its secondary host. It is distributed across the United States on two hosts: the eastern cottonwood (Populus deltoides), on which it is sympatric with Pemphigus populitransversus, and the Fremont cottonwood, (Populus fremontii) on which that species is absent. The two aphid species were confused for many years. Pemphigus obesinymphae is widely distributed in the USA, and probably in northern Mexico, whilst Pemphigus populitransversus is only found in eastern USA.
In spring Pemphigus populi form green or greenish-yellow globular outgrowths of the mid-rib of the leaves of black poplar (Populus nigra) which are close to the base of the leaf (see first picture below) (cf. Pemphigus gairi & Pemphigus phenax which form yellowish or reddish elongate pouch-shaped galls which are more or less in the middle of a leaf). The outgrowths become club-shaped with the basal part narrower than the apex when mature.
The mature alatae (see first picture above) are greyish green with abundant wax. They have small but distinct marginal wax gland plates. The terminal process of the antenna (see second picture above) is 0.25-0.4 times as long as the basal part of the sixth antennal segment. They have 3-9 secondary rhinaria on the third antennal segment, 1-3 rhinaria on the fourth segment and 0-2 on the fifth segment. The sixth antennal segment is always without secondary rhinaria (cf. Pemphigus populinigrae, and Pemphigus gairi & Pemphigus phenax which all have some secondary rhinaria on the sixth antennal segment.) The apical segment of the rostrum is about 0.5-0.7 times as long as the second segment of the hind tarsus. Siphuncular pores are absent (cf. Pemphigus populinigrae, Pemphigus bursarius, Pemphigus gairi & Pemphigus phenax which all have siphuncular pores). The body is 1.5-2.4 mm long. Pemphigus populi host alternates from various poplar species, mainly black poplar (Populus nigra) and Lombardy poplar (Populus nigra 'italica'), to the roots of various species of Fabaceae, especially meadow vetchling (Lathyrus pratensis), black medic (Medicago lupulina) and tall melilot (Melilotus altissimus).
In spring, Pemphigus populicaulis fundatrices form yellowish-green to creamy (sometimes reddish?) galls formed of the swollen base of a poplar leaf twisted with the broadened petiole (see first picture below). As such, the gall is very similar to those of two other American species, Pemphigus nortonii and Pemphigus populiglobuli. However, the exit from the gall for alatae is a small round hole on the underside between leaf and petiole (see second picture below) (cf. Pemphigus nortonii and Pemphigus populiglobuli, which have gall exits as a slit on the underside between the leaf and petiole). The galls are 10-13 mm in diameter. The fundatrix (not pictured) is pale yellowish to creamy, with a frosted appearance and slightly dusky appendages. The rostrum reaches between the first and second pair of coxae. Wax glands are in 6 dorsal rows, with none on the head. The body length of the Pemphigus populicaulis fundatrix is 2-2.9 mm.
Images above copyright Megachile, under a public domain licence.
The emigrant alate (see third picture above) has a blackish-brown head and thorax, a yellowish olive-green abdomen covered with blue-grey wax, and dusky brown appendages. The rostrum reaches between the first and second pair of coxae. There are 3-7 secondary rhinaria on the base of antennal segment VI (cf. Pemphigus nortonii, which has 5-11 rhinaria on the base of segment VI). The body length of adult Pemphigus populicaulis alatae is 1.7-2.0 mm. Pemphigus populicaulis usually galls eastern cottonwood (Populus deltoides), but has also been recorded from other cottonwoods and quaking aspen (Populus tremuloides). Alatae emerge in July-September, and depart for an unknown secondary host. Water parsley (Oenanthe sarmentosa) and corn roots (Zea mays) have both been suggested, but neither has been confirmed. Pemphigus populicaulis is widely distributed in North America.
In spring the fundatrices of Pemphigus populiglobuli induce galls at the base of cottonwood leaves (usually Populus angustifolia, Populus balsamifera or Populus trichocarpa). The galls are green, often tinged with red and/or yellow when mature (see first picture below). They are globular, conical or bullet-shaped, and are formed by swelling of the base of the leaf lamina and thickening of the petiole. The exit hole from the gall is a slit on the underside between leaf and petiole (cf. Pemphigus populicaulis which has a small round hole on the underside between leaf and petiole as the exit hole). The slit in the gall is rarely equal to one-half the circumference of the gall and is not visible from above. The lip-like borders of the opening are frequently quite rough. Maxson & Knowlton (1929) note that galls located at some distance from the base of the leaf and resembling those produced by Pemphigus populivenae sometimes occur, especially on heavily infested trees.
First two images above copyright James Bailey; third image copyright myrtus; The Pemphigus populiglobuli fundatrix has wax glands present on the entire body, and is coloured yellowish or green. The immature offspring of the fundatrix (see second picture above) are pale yellow. They all develop to emigrant alatae (see third picture above). The alate Pemphigus populiglobuli is lightly dusted over with a whitish powder, which gives it a bluish tinge. The head and thorax are dark, almost black, and the abdomen is greenish-yellow. There is a broad dusky band along the posterior margin of the pterostigma, and the wing veins are slightly dusky to brownish. The venation is normal for the genus. Antennae are 6-segmented. The antennal terminal process is short, but is usually longer than 0.03 mm and more than 1.5 times its basal width (cf. Pemphigus populicaulis, which has the terminal process usually shorter than 0.03 mm, and less than 1.5 times its basal width). Annular secondary rhinaria are distributed 6-13 on segment III, 2-4 on segment IV, and 2-4 on segment V, and 3-5 on segment VI. The body length of the alate Pemphigus populiglobuli is 1.5-2.3 mm. Pemphigus populiglobuli is assumed to host alternate from its primary host, cottonwood (usually Populus angustifolia, Populus balsamifera or Populus trichocarpa = Populus balsamifera ssp. trichocarpa) to a currently unknown secondary host. In Alberta, alatae depart the primary host in June-early July (Harper, 1959). The species is widely distributed in North America.he species is widely distributed in North America.
In spring, the fundatrices of Pemphigus populinigrae induce yellowish or dull reddish broad pouch-shaped galls (see first picture below), on the midrib of the upperside of leaves of poplar (mainly Populus nigra). Mature galls are rounded and smooth on top and are sometimes partially subdivided. (cf. Pemphigus gairi and Pemphigus phenax which induce reddish elongate galls often tinged with yellow laterally). The galls of Pemphigus populinigrae are usually located near the middle of the leaf and open on the underside of the leaf. The fundatrices (not pictured) are green or greyish green, and have no siphunculi. They have 4-segmented antennae which are about 0.17 times the length of the body.
The winged migrants (see second picture above) from the primary host are dark green with a slight covering of powdery wax. Along the upper surface of the abdomen there are six rows of more-or-less fused wax-glands. The six segmented antennae of the emigrant alatae (see pictures below) are about 0.3-0.4 times the length of the body, with a rather indistinct terminal process. Secondary rhinaria extend almost to the base of the third antennal segment, so that the small "tooth" on the inner side is distal to the most basal rhinarium. The third antennal segment has 12-18 secondary rhinaria, the fourth has 3-7 secondary rhinaria, the fifth has 4-7 secondary rhinaria, and the sixth has 4-7 secondary rhinaria (cf.Pemphigus populi whose alatae have no secondary rhinaria on antennal segment VI). There is no brown shadowing around the wing veins. Siphunculi are present but small and indistinct. Alatae of Pemphigus populinigrae emerge from the galls on poplar in June-August and migrate to found colonies above ground on the stems, leaves and flowers of cudweeds (Filago, Gnaphalium). Apterae on the secondary hosts are yellow-green, with white wax-wool. The adult body length is 2.0-2.2 mm. Sexuparae return in September-October to black poplar where the female oviparae lay overwintering eggs. Pemphigus populinigrae is found throughout Europe and across Asia to east Siberia.
Feeding by the fundatrix of Pemphigus populiramulorum induces a gall on the host, usually cottonwood (Populus deltoides ssp. occidentalis). Floate (2010) describes how feeding on the young twigs causes swelling of the tissues that expand into a hollow globular structure that surrounds the fundatrix and her offspring (see first picture below). The location of galls on the woody tissues of the twig results in empty galls frequently remaining on the tree during winter months. Sometimes galls are produced not on the twig, but at the base of a leaf petiole (cf. Pemphigus obesinymphae, which produces a globular gall on the petiole close to the leaf blade; and cf. Pemphigus populitransversus, which produces its gall mid-petiole). The gall is green or brownish, normally globular, and about 25 mm in diameter. The exit opening is a narrow transverse slit with slightly protruding lips. The slit does not always open along the same axis, so Pemphigus populiramulorum galls are of variable appearance.
The fundatrix in the gall (not pictured) is pale creamy yellow with dusky appendages. The rostrum rarely reaches the second pair of coxae. Wax gland plates are in 6 longitudinal rows on the abdominal dorsum. These produce abundant wax. The immature offspring of the Pemphigus populiramulorum fundatrix (see second picture below) are orange-yellow or pale yellow, and develop to emigrant alatae.
First two images above copyright Whitney Cranshaw, third image copyright BG Photography Group The emigrant alate Pemphigus populiramulorum (see above) has the head and thorax black, the abdomen dark olive, and the appendages dusky. Secondary rhinaria are distributed 9-11 on antennal segment III, 0-5 on IV, 0-4 on V, 0-5 on VI. Antennal segment V is 0.8-1.0 times segment IV (cf. Pemphigus populicaulis, which has V 1.0-1.2 times IV). Siphunculi are plainly evident. The rostrum reaches between the first and second pairs of coxae. Body length of emigrant alatae is 2.2-2.5 mm. The main primary host is plains cottonwood (Populus deltoides ssp. occidentalis). It was first described from balsam poplar (Populus balsamifera), and has also been found on Fremont cottonwood (Populus fremontii). Emigrant alatae leave the galls in July-September, but their secondary host is unknown. Pemphigus populiramulorum has been found over most of western North America from Alberta, Canada to Colorado, USA.
Overwintering eggs of Pemphigus populitransversus on eastern cottonwood (Populus deltoides) hatch in spring. Immature fundatrices feed on the leaf petioles of its host. This induces the swelling of tissues that form a hollow globular structure - the gall - that surrounds each fundatrix and her offspring (see first picture below). This gall is green, often with some reddish shading, and usually has an open transverse slit (cf. the gall of Pemphigus populicaulis, which has one or two small openings in the semi-spiral groove, that extends two-thirds of the diameter of the gall, formed by the twisting of the petiole upon itself; and cf. the gall of Pemphigus populiramulorum, which develops upon the side of tender growing twigs). The adult Pemphigus populitransversus fundatrix is whitish to pale dirty greenish yellow. She produces 150-200 heavily waxed offspring which develop (at least most of them) within the protective cover of the gall (see second picture below).
First & third image above by permission, copyright Claude Pilon, all rights reserved. Alate Pemphigus populitransversus (see third picture above) start to emerge in July, with most having exited by late August. Under a microscope these emigrant alatae can be discriminated from those of closely related species. On antennal segment VI Pemphigus populitransversus has an enlarged primary rhinarium, with islands, like that on V. This rhinarium is less than 0.05-0.08 mm long, and occupies under half of the length of base of antennal segment VI. There are 2-7 Secondary rhinaria on 2-7 antennal segment III, 0-1 on segment IV, rarely 1 on segment V but none of the base of segment VI (cf. Pemphigus tartareus, which has 10-15 secondary rhinaria on segment III, 4-5 on segment IV, 2-4 on segment V and 3-5 on the base of segment VI). Separation from Pemphigus obesinymphae requires examination of the embryos within the emigrant alatae. Embryos of Pemphigus populitransversus have the tip of the rostrum not extending beyond the first segment of their fore tarsi (cf. Pemphigus obesinymphae, where embryos in the emigrant alatae have the tip of their rostrum extending beyond first segment of the fore tarsi). The Pemphigus populitransversus alatae have small siphuncular pores present. Emigrant Pemphigus populitransversus alatae found colonies of aphids on the roots of cabbage (Brassicaceae) (see picture above), where it can be a serious pest. The wingless viviparae are a 'sordid pale yellow, with head, antennae, and legs dusky brown to blackish and the tarsi and eyes black". Early studies suggested there were no wax glands on the body, but in Bugwood Sparks & Riley describe the nymphs that develop on Brassica roots as being covered with a bluish-white wax (see their picture, second above) giving them a grey appearance. In their native America sexuparae return to cottonwood in September-October to produce sexuales which lay overwintering eggs on the bark. In areas where it has been introduced, the population remains on the roots of the secondary host throughout the year as an anholocyclic population. Pemphigus populitransversus is recorded throughout most of North America east of the Rocky Mountains. It has also been reported on Populus species in Mexico, Chile, South Africa and the Azores, and as anholocyclic populations on Brassicaceae roots in New Zealand and England.
In spring, Pemphigus protospirae forms green, or green mottled with red, smooth galls formed by slight thickening, flattening and spiral twisting of the leaf petiole of Populus nigra (black poplar). The galls of Pemphigus protospirae have more than three, and usually more than five twists (see picture below, cf. the gall of Pemphigus spyrothecae which is thicker and has 2-3 twists). The fundatrix that induces the gall has antennae about 0.2 × the length of the body and lacks siphunculi.
Image courtesy of Dimìtar Nàydenov under a Creative Commons Attribution-Share Alike 3.0 Unported license.
All the Pemphigus protospirae fundatrix offspring are winged. These offspring leave the gall during late spring to early summer (cf. the alate females that bear the Pemphigus spyrothecae sexual generation, which leave the gall from late August to November). Pemphigus protospirae winged migrants are greyish-green and lightly covered with waxy powder. Their antennae are 0.33 - 0.40 times their body length. The primary rhinarium on the fifth antennal segment is larger than that on the sixth, and is not fringed with hairs (cf. Pemphigus spyrothecae which has a small oval or rounded primary rhinarium on the fifth antennal segment, no larger than that on the sixth, and fringed with very fine short hairs). The most proximal rhinarium on third antennal segment is distal to the tooth. The number of secondary rhinaria on the third antennal segment is 10-14, on the fourth 2-5, on the fifth 2-4, and on the base of the sixth 2-8. Small siphuncular pores are present. Winged migrants of Pemphigus protospirae emerge from their galls on poplar in late May to early July and move to aquatic umbellifers (Apiaceae) as secondary hosts. Pemphigus protospirae is less common than Pemphigus spyrothecae, probably because it is restricted by the localized distribution of its secondary hosts. Pemphigus protospirae is widely distributed in Europe, across to west Siberia and central Asia. The winged migrants move to aquatic umbellifers (Apiaceae) as secondary hosts.
In spring, Pemphigus spyrothecae form green, reddish or yellowish, smooth galls formed by thickening, flattening and spiral twisting of the leaf petiole of Populus nigra (black poplar) with 2-3 twists (see picture below) (cf. the gall of Pemphigus protospirae which is thinner and usually has more than five spirals). The Pemphigus spyrothecae fundatrix is pale green, giving rise to a second generation of apterae within the gall.
The emigrant winged sexuparae emerge from the gall in late summer or autumn (cf. the emigrant alates of Pemphigus protospirae which emerge from the gall in late spring and early summer). They have a small oval or rounded primary rhinarium on the fifth antennal segment, no larger than that on the sixth, and fringed with very fine short hairs. (cf. Pemphigus protospirae where the primary rhinarium on the fifth antennal segment is larger than that on the sixth, and is not fringed with hairs). The emigrant alate of Pemphigus spyrothecaehas no secondary rhinaria on the fifth and sixth antennal segments (cf. Pemphigus protospirae which has 2-4 secondary rhinaria on the fifth, and 2-8 on the base of the sixth). Pemphigus spyrothecae does not host alternate, but remains on Populus nigra (black poplar) all year. The fundatrix gives rise to a second generation of apterae within the gall, and the alate sexuparae emerge in August to November when they produce males and oviparae on the bark (cf. the emigrant alatae Pemphigus protospirae which leave the gall during late spring to early summer). The poplar spiral gall aphid is found throughout Europe as well as in North Africa, western Siberia and Pakistan, and has been introduced to Canada.
Adult apterae of Pemphigus trehernei on the roots of sea aster, its secondary host, are yellowish white to greenish white (see first picture below). They are covered with greyish white wax which forms tufts on the abdomen, and also coats the roots upon which they feed (see second picture below). Characteristics which separate the 'bursarius' group of species (which includes Pemphigus trehernei) from other Pemphigus species, are: (a) the subgenital plate has a total of 13-16 hairs and (b) the last antennal segment (including the terminal process) is 0.89-1.24 times longer than the second hind tarsal segment. There are no morphological characters that can be used to differentiate apterae of Pemphigus species within the 'bursarius' group such as Pemphigus phenax, Pemphigus gairi, and Pemphigus bursarius. The body length of the adult Pemphigus trehernei aptera is 1.3-2.4 mm.
The emigrant alate of Pemphigus trehernei from poplar (obtained by experimental transfer) has antennal segment III 0.30-0.40 times the length of the hind tibia. Secondary rhinaria are distributed 11-19 on antennal segment III, 4-8 on segment IV, 4-10 on segment V and 6-11 on segment VI. Pemphigus trehernei has only been found naturally on its secondary host, sea aster (Tripolium pannonicum). Aphid populations are largely confined to the edges of creeks and saltpans. Alate sexuparae are produced in September to December but overwintering of parthenogenetic generations on the roots of Aster tripolium is common. Alate sexuparae of Pemphigus trehernei have been transferred experimentally to Lombardy poplar (Populus nigra var. italica), and subsequent generations produced globular green galls with a reddish tinge around the exit hole. Pemphigus trehernei has only been recorded from England, Ireland and France.
In spring the fundatrices of Pemphigus vesicarius induce galls on their primary host, black poplar (Populus nigra). The gall (see first picture below) originates on a leaf upper-side from the base of its mid-rib. The gall develops in April-May into an irregular pale green structure with numerous tubular outgrowths, that covers the whole leaf. The fundatrix (see second picture below), which lives and feeds inside the gall, is dark slate-grey to blue-black and covered with wax.
Images above copyright Dr László Érsek, all rights reserved.
The mature fundatrix produces large numbers of offspring which develop within the gall and feed on the gall wall (see first picture below). By their fourth instar the developing wings of the offspring are visible (see second picture below), and by May most have matured to alatae.
The adult Pemphigus vesicarius alate (not pictured) can be distinguished from Pemphigus populi alatae by the following characters: The first tarsal segments usually have 3-4 hairs on at least some tarsi (cf. Pemphigus populi, which almost always has 2 hairs on the first tarsal segments). Secondary rhinaria are elongate oval, and extend less than half way around the antenna. They have 6-11 secondary rhinaria on antennal segment III, 1-4 on segment IV, and 0-2 on segment V (cf. Pemphigus populi, which has 3-9 secondary rhinaria on antennal segment, 1-3 on segment IV, and 0-2 on segment V). Siphuncular pores are absent. The body length of a Pemphigus vesicarius alate is 1.7-3.0 mm. Alatae leave the gall in May-June through secondary holes at the apices of outgrowths and migrate to found colonies on the stems and basal parts of Colutea arborescens (bladder senna. The apterae on Colutea secrete abundant wax and have a body length of 2.7-3.0 mm. Pemphigus vesicarius is found in southern Europe, Algeria, south-west and central Asia, east to Pakistan and India.
Whilst we make every effort to ensure that identifications are correct, we cannot absolutely warranty their accuracy. We have mostly made identifications from high resolution photos of living specimens, along with host plant identity. In the great majority of cases, identifications have been confirmed by microscopic examination of preserved specimens. We have used the keys and species accounts of Blackman & Eastop (1994) and Blackman & Eastop (2006) supplemented with Blackman (1974), Stroyan (1977), Stroyan (1984), Blackman & Eastop (1984), Heie (1980-1995), Dixon & Thieme (2007) and Blackman (2010). We fully acknowledge these authors as the source for the (summarized) taxonomic information we have presented. Any errors in identification or information are ours alone, and we would be very grateful for any corrections. For assistance on the terms used for aphid morphology we suggest the figure provided by Blackman & Eastop (2006).
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