Pemphigus populicaulis Fitch

The gall is yellowish green to creamy, formed by swelling of base of leaf lamina, twisted around broadened petiole, rather like that of P. nortonii and P. populiglobuli but with a small, rounded exit hole on the underside (Palmer 1952, Harper 1959a). Especially associated with P. deltoides and P. deltoides ssp. occidentalis (= monilifera), but also recorded from other cottonwoods and P. tremuloides. The fundatrix is pale yellowish to whitish green. Alatae (BL 1.7-2.0 mm) emerge in July-September. The secondary host has not definitely been established; Glendenning (1924) reported that it was Oenanthe sarmentosa, but did not provide evidence for this assertion. Hottes & Frison (1931) suggested that P. brevicornis Hart, described from corn roots, was the sexupara of populicaulis. Widely distributed in North America. Setzer (1985) studied gall mortality. Sokal et al. (1980) and Bird et al. (1982) studied geographical variation in eastern North America using multivariate techniques.

Pemphigus populi-caulis Fitch

Gall. Yellowish green to creamy, formed of swollen base of leaf twisted with broadened petiole; exit a small round hole on underside between leaf and petiole. Size 10-13 mm in diameter

Cellections. As winter host on Populus sargenti and rarely P. acuminata, in twisted petiole and leaf galls; alternate host unknown. Throughout Colorado and nothern Utah. Fundatrices June 12 to Aug. 29, alate fundatrigeniae June 20 to Aug. 29; common.

Chief Distinguishing Characters. Character, of gall with round exit hole.

This species is very close to P. bursarius (Linnaeus) and distinguished most certainly by form of gall. However, a number of collections of specimens ap parently inseparable from P. populicaulis have been taken in petiole galls re sembling those of P. populi-transversus. Galls of P. bursarius according to Tull gren (1909:114) and Theobald (1929:245) differ in more protruding lips. The question of the status of these forms requires further biological work.

Pemphigus populicaulis Fitch

Gall on Populus sargentii [deltoides] formed by swelling and twisting of petiole and leaf blade

P. populicaulis is more common in southern Alberta than any other gall-forming aphid on poplar. The galls are found on trees along river banks and in many of the shelter belts in the irrigated areas. The primary host of this species in Alberta is P. sargentii Dode.

The gall caused by this aphid is also formed at the junction of the petiole and blade of the leaf and is produced by a swelling and twisting at the base of the blade and at the top of the petiole (Fig. 3). In this respect it is similar in formation to the gall caused by P populiglobuli but differs in that it has a small, round exit (Fig. 19) whereas the exit of the gall caused by P. populiglobuli is a long, narrow, angular slit. When two galls of P. populicaulis are found on a single leaf, their shapes vary slightly from those of single galls (Fig. 19).

In 1924 Glendenning reported water parsley, Oenanthe sarmentosa Presl, as the secondary host of P populicaulis. Strickland ( 1953) recorded Pemphigus brevicornis Harr. from potatoes, beets, and celery in August and September. Hottes and Frison (1931) collected P. brevicornis on roots of an umbrella plant, Erigeron sp., and a goldenrod, Solidago sp., and stated that the specimens might be the sexuparae of P. populicaulis. Cutright (1925) considered P. brevicornis as a synonym of Pemphigus lactucae Fitch. Thus, if Hottes and Frison and Cutright are correct, the name P. populicaulis will be replaced by P. lactucae, which has priority.

Records of the distribution of P. populicaulis in Alberta are as follows: 1950, Picture Butte, Lethbridge, Coaldale, Taber, Vauxhall, Grantham, Turin, Iron Springs, Monarch, Macleod, Barnwell, Welling, Populus sargentii; 1953, Medicine Hat; 1957, Nobleford, Populus sargentii.

Pemphigus populicaulis Fitch 1859 [Poplar leaf-petiole gall aphid].

Galls are initiated on the upper leaf surface, with blade and petiole becoming twisted to form a more or less globular structure at the juncture of the leaf petiole and the leaf blade. The structure is composed of petiole tissue but also includes tissues of the leaf blade that usually extend some distance down onto the gall (Figs. 9 and 10). Twisting of the leaf tissues forms a semi-spiral groove that extends two-thirds of the diameter of the gall. One or a few small round openings in the groove of mature galls provide an exit for alatae. An average of 410 alatae per gall was reported for Quebec (Alleyne and Morrison 1977). An average of 123 alatae per gall (range: 8-426) was reported for southern Alberta, with their exiting from galls beginning in late June to mid-July and being 90% complete by September 11 (Harper 1959b).

The primary host is P deltoides (Palmer 1952; Harper 1959; Alleyne and Morrison 1977; Floate and Whitham 1993). Rare occurrences of P populicaulis have been reported on intersectional hybrids (Gillette and Palmer 1934; Floate and Whitham 1993). Secondary hosts include water parsley (Apiaceae: Oenanthe sarmentosa C. Presl ex DC.) and possibly fleabane (Erigeron spp.) and goldenrod (Solidago spp.) (Asteraceae) (refs. in Harper 1959a). Harper (1959a) cited references that raised the possibility that P populicaulis might be synonymous with P brevicornis. This synonymy is not supported in more recent work (Eastop and Hille Ris Lambers 1976).

Pemphigus populicaulis

An irregularly spherical gall at union of blade and petiole. The opening is closed by a twisting of the leaf. Common on several poplars. The insects emerge when the gall dries somewhat and opens, usually about the middle of the summer.

Pemphigus populicaulis

Twisted, subglobular galls with oblique openings at base of cottonwood leaves, diameter .25 to .5 inch, aphid

Pemphigus populicaulis
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Hosts: Populus tremuloides, balsamifera subsp trichocarpa, several cottonwoods

This gall, unlike the preceding species, has a spiral slit along which a series of small holes develop later in the season, through which aphids squeeze out.

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.