Pemphigus populiglobuli

Galls are semi-globular structures formed by the swelling of the leaf blade at the junction with the petiole and extend above the plane of the upper leaf surface (Fig. 11). Although morphologically similar to galls of P. populicaulis, galls of P. populiglobuli typically have a long, narrow slit between the modified tissues of the leaf blade and the petiole, whereas galls of P. populicaulis have a small, pore-like opening. Mature galls are green, often with a reddish tinge. In southern Alberta, galls produce an average of 56 (range: 8–174) alatae, with their exiting from galls beginning in late June to early July and being 90% complete by July 20 (Harper 1959 b).

Primary hosts include P. angustifolia, P. balsamifera, and hybrid intermediates (Maxson and Knowlton 1929; Gillette and Palmer 1934; Harper 1959 a; Floate and Whitham 1993). However, the key in Alleyne and Morrison (1977) associates P. populiglobuli with P. deltoides .

Pemphigus populi-globuli Fitch

Gall. Pale yellow or red. Composed mostly of swollen leaf base and flat but broadened petiole; exit hole a slit on underside between leaf and petiole.

Collections. As winter host in petiole and leaf gall on Populus angustifolia and P. “balsamifera (?)" (probably P. candicans or deltoides since the localities recorded are out of the habitat range of P. tacamahaca). Utah: Throughout northern part of state. Colorado: Buckhorn Creek near Masonville), Longmont and Monte Vista. Fundatrices June 24 to July 4, alate fundatrigeniae July 4 and (dead specimens in gall) Aug. 18; rare.

This species is very close to P. populi-caulis and only doubtfully separated by host, shape of gall which is without definite round exit hole and length of III in fundatrigenia (not distinctly longer than hind tarsal II, longer than hind tarsal II in P. populi-caulis).

Pemphigus populiglobuli Fitch

The gall is green, often tinged with red and/or yellow when mature; globular, conical or bullet-shaped, formed by swelling of base of leaf lamina and thickening of petiole, the exit hole being a slit on the underside between leaf and petiole (Maxson & Knowlton 1929). Primary hosts are Populus angustifolia and P. balsamifera, more rarely P. trichocarpa. The fundatrix is variously reported to be dark green (Palmer 1952) or pale yellowish white (Maxson & Knowlton 1934). Alatae (BL 1.5-2.3 mm) leave gall in June-early July (Alberta; Harper 1959b) for an unknown secondary host. Widely distributed in North America. Differences from P. populicaulis and other closely-related species are discussed by Maxson & Knowlton (1929).

Pemphigus populiglobuli Fitch

Gall formed by swelling and twisting of petiole and leaf blade of Populus angustifolia James or Populus balsamifera L. (or, rarely, Populus trichocarpa T. and G.)

The primary hosts of P. populiglobuli in Alberta are P. angustifolia, P. balsamifera, and, rarely, P. trichocarpa. The gall is formed at the junction of the petiole and leaf blade and is produced by a swelling at the base of the blade and at the top of the petiole (Fig. 2). The exit slit is produced by a slight separation of the twisted parts of the petiole and blade. Usually the gall is green but it may have a reddish tinge.

Records of the distribution of P. populiglobuli in Alberta are as follows: 1954, Lethbridge, Magrath, Cardston, Coaldale, Picture Butte, P. angustifolia, P. balsamifera; 1957, Pincher Creek, Black Diamond, Lundbreck, Coleman, Blairmore, Crowsnest, Cyprus Hills, Medicine Hat, Waterton, Monarch, Macleod, P. balsamifera, P. angustifolia, P. trichocarpa

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 populi-globuli Fitch

The Galls.—The galls are usually semi-globular. Not infrequently they are more or less cone-shaped. Normally located galls are situated at the base of the leaf, on its upper side. The color is green, or when exposed to the tinged with reddish varied with yellow. The gall is composed of a much enlarged and thickened portion of the leaf blade. On the under side there is a somewhat curved mouth-like orifice bounded on one side by the much thickened midrib and on the other by a thickened fold in the leaf blade. A more or less broken portion of the blade usually extends along this fold nearly the entire length of the mouth.

Many times the blade of the leaf stands at an angle to the petiole. The opening 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. Galls located at some distance from the base of the leaf and resembling those produced by P. P.-venæ sometimes occur, especially on heavily infested trees.

This aphid is frequently encountered in Utah, on balsam poplar, Populus balsamifera. It has been collected in this state from Big Cottonwood Canyon, Blacksmith Fork Canyon, Farmington, Hyde Park, Providence, and Salt Lake City. The material described was collected at Salt Lake City.