Pemphigus spyrothecae

Pemphigus bursarius

Pemphigus populitransversus

Pachypappa pseudobyrsa

Pemphigus populicaulis

Pemphigus populiglobuli

Pemphigus tartareus

Thecabius gravicornis

Thecabius populiconduplifolius

Pemphigus monophagus

Pemphigus spirothecae

Galls on Lombardy poplar (Populus nigra var italica) formed by both twisting and swelling of the petiole

This aphid produces galls in early spring on the petioles of Lombardy poplars and has long been known to occur on poplars in Europe (Connold 1901; Theobald 1929; Stroyan, pers. comm.). No previous record of this aphid exists in North America. The feeding activity of the stem mother causes the petiole to twist into a spiral. The spiralling continues until the stem mother is completely surrounded by petiole tissue (Fig. 1). Within this spiral the stem mother reproduces and the gall swells, producing a large cavity in which the aphid progeny develop. Unlike P. bursarius galls which mature in early summer, galls of P. spirothecae mature in late August and early September. This is primarily attributable to the monoecious life cycle of P. spirothecae which produces one migrant form, the sexupara, within the mature gall. This form corresponds to that of P. bursarius produced on the roots of alternate hosts. 

As galls of P. spirothecae mature they change from green to pale red and a variable number of tiny pores appear along the seams (Fig. 3). Much larger openings may develop on this region of the gall, facilitating mass release. At leaf-fall, large numbers of apterae and alates are still found within the galls. Galls of P. spirothecae aphids were extremely abundant on Lombardy poplars in regions surveyed. 

Pemphigus bursarius

Galls on Lombardy poplar (Populus nigra L. var. italica Muenchhausen) formed by petiole swelling only, no twisting

This aphid is regarded as a major pest of lettuce in Europe (Dunn 1959; Judge 1967; Stroyan 1964) and in the United States (Lange et al. 1957; MacDaniel 1958). Little is known concerning this species in Canada although Harper (1966) found them on Lombardy poplar in Alberta and indicated that it has the potential of becoming a rather important lettuce pest in North America. Reports of attacks by this aphid on lettuce in Nova Scotia (Creelman 1969) and in Quebec (Lange and Cartier, pers. comm.) are further indicators. The primary author is currently engaged in a study of this species. 

The galls of P. bursarius are flask-shaped (Fig. 4) and are formed on the petioles of leaves of Lombardy poplars. Quite often as many as three or four galls may be present on a single leaf petiole. In such instances the shape of the gall is modified depending on the degree of overlap (Fig. 5). Surveys of poplars conducted during 1972 and 1973 in regions on the west end of Montreal Island and in Pincourt, Ile Perrot, Que., indicate that each gall is the product of a single stem mother or fundatrix hatched in early spring from an overwintering egg. An average of 78 alates per gall were produced by 20 galls examined, and these alates escape from the gall cavity during mid-June and mid-July (by means of tiny pores on the lip). Present studies indicate that this aphid colonizes many alternate hosts, but lettuce is the only one of economic importance. 

Pemphigus populitransversus

Galls on Populus deltoides, formed by swelling of petiole. Galls bear a transverse slit-like opening

This aphid, which is indigenous to North America, forms galls on cottonwood poplars. The gall resembles that of P. bursarius but migrant release is by means of a transverse slit on the lip (Fig. 6). An average of 150 migrants of this aphid were produced by 20 galls. P. populitransversus has been the subject of many investigations in the United States. Jones and Gillette (1918) showed that this aphid attacked turnips in summer. More recently Wene and White (1953), Wolfenbarger (1965), Chalfant (1969), and Harding (1971) have found this aphid to be a serious pest on cabbage. MacNay (1955) recorded this species in Alberta on Populus deltoides, P. tremuloides, and P. angustifolia.

Asiphum pseudobrysum

Pseudogalls on Populus deltoides formed on or beside the midrib on ventral leaf surface

Pseudogalls of this aphid were found in large numbers on leaves of cottonwood. These malformations were all formed on the mid-rib by the stem mother which feeds on the underside of the leaf blade (Figs. 7, 8). The cavity produced is much too small to accommodate the aphid progeny which crawl from the cavity and feed on the secondary veins. The lower surface of the leaf becomes coated in a white powdery wax produced by the apterae. The stem mother remains within the cavity. As feeding proceeds the two halves of the leaf blade move towards each other ventrally so that the surfaces are almost parallel. An average of 625 alates were produced from 15 pseudogalls. 

Pemphigus populicaulis

Galls on Populus deltoides formed at junction of leaf blade and petiole by twisting and swelling with pore-like openings

This is the most common of the aphids forming excrescences on cottonwood in Quebec. The stem mother feeds at the petiole leaf-blade junction on the underside of the leaf. As a result of this feeding activity the petiole bends, sandwiching the stem mother between petiole and leaf blade. Once completely enclosed the stem mother reproduces, an average of 410 alates being produced from 20 galls examined. As the gall matures the upper surface becomes convex and changes in colour from green to red (Fig. 9). A series of small pores develop along the seam on the underside of the gall (Fig. 10) and migrants squeeze through them. Harper (1959) found this gall throughout Alberta on Populus sargentii Dode. Glendenning (1 924) reported water parsley, Oenanthe sarmentosa Presl., as an alternate host. Colonization trials involving a wide range of annual plants are currently under investigation.

Pemphigus populiglobuli Fitch

[The photos included are identified as either this gall or P populicaulis as if the authors could not determine which or meant the photo to stand in for both. According to all other sources these two galls are easily distinguished by their host group; populiglobuli is only known from sect. Tacamahaca.]

Galls on Populus deltoides Marsh [this host relation disagrees with every other source and is presumably a mistake] formed at junction of leaf blade and petiole by twisting and swelling with angular slit-like openings

This aphid forms galls which are only differentiated from P. populicaulis with difficulty. The character at present used to differentiate between galls of P. populicaulis and P. populiglobuli is the type of migrant exit produced. In galls of the latter aphid an angular slit is produced along the seam on the lower gall surface. These galls were far fewer than those of P. populicaulis and accommodated a wide range of aphid predators. No alternate host is known for this aphid.

Pemphigus junctisensoriatus Maxson

Galls on Populus deltoides formed at junction of leaf blade and petiole by twisting and swelling almost spherical on upper surface, largely formed from petiole, with angular slit-like opening 

Galls of this aphid were also collected from cottonwood, and resemble P. populicaulis in their location and method of development. The upper gall surface is almost spherical and is formed primarily of petiole tissue (Fig. 11). Migrant escape is by means of a slit along the seams on the lower gall surface. This aphid species was reported from galls by MacNay (1955) in Canadian Insect Pest Review, but Maxson has subsequently checked the material and identified the aphid present as P. nortonii Maxson (Harper 1959). Galls of P. junctisensoriatus were all collected from a single medium-sized cottonwood at Macdonald College Campus, Quebec. No alternate hosts are known. 

Thecabius gravicornis (Patch)

Galls on Lombardy poplar (Populus nigra L. var. italica Muenchhausen) Pseudogalls formed by folding of young terminal leaves of Lombardy poplar [also keys to Thecabius populicondupliflius]

Pseudogalls of this aphid were found on most young, terminal leaves of a single Lombardy poplar plant at Pincourt, on Ile Perrot, just off the west tip of the Island of Montreal, Que., in the spring and summer of 1973. The stem mother feeds on the mid-ribs on the lower surface of the leaf. This results in the formation of a cavity (Fig. 12) in which the first generation apterae are produced. These apterae leave the confines of this cavity to feed on the young terminal leaves. The leaves fold ventrally (Fig. 13), and winged migrants are produced within the cavity between mid-June and early July.

Thecabius populiconduplifolius (Cowen)

Galls on Lombardy poplar (Populus nigra L. var. italica Muenchhausen) Pseudogalls formed by folding of young terminal leaves of Lombardy poplar [also keys to Thecabius gravicornis]

Alates of this aphid were collected from pseudogalls similar to those already described for T. gravicornis above, on terminal leaves of Lombardy poplars in Pincourt, Ile Perrot. Only few alates were present, and these were present amongst large numbers of T. gravicornis alates. Separation of the alates of these two aphid species is readily possible on the structure of the antennae. 

Because of the large numbers of leaves bearing pseudogalls and thus the very close association of the aphid species, it is quite possible that they may be variants of the same species, although they are currently regarded as separate. Harper (1966) collected aphids with asymmetrical antennae from pseudogalls on poplars in Alberta, one aphid showing characteristics of T. affinis and the other of T. populiconduplifolius. 

T. populiconduplifolius was first reported from Populus monilifera Aiton (P. deltoides Marsh) in Colorado (Cowen 1895). Palmer (1952) also reported it from Colorado on Populus sargentii Dode, whilst Harper (1966) reported it from Populus balsamifera L. in Lethbridge, Alta. Gillette (1914) traced this aphid to populations on Ranunculus sp. 

Pemphigus monophagus Maxson

Tough, leathery galls formed on or adjacent to the mid-rib on leaf blade of Populus balsamifera 

This was not found in the areas surveyed in Quebec. It was first reported from Populus angustifolia and P. tacamabaca in Colorado by Maxson in 1934. Galls of this aphid were extremely numerous on leaves of balsam poplar, P. balsamifera L., at Crystal Springs on the west side of Pigeon Lake in Alberta during the summers of 1972 and 1973. The galls are rather tough and leathery and are produced as projections on the upper leaf surface on both sides of the mid-rib (Fig. 14) as a result of the feeding activity of the stem mother on the lower mid-rib region. This aphid is monoecious, the alates emerging in late August and early September. 

Some Canadian poplar aphid galls