Aphid Gall (Unclassified),

Host Populus balsamifera L.

A pouch-like gall on the under surface of the leaf, produced by a fold in the blade near the base of the midrib. One edge of the fold is attached along this midrib. The slit-like opening, which is on the upper surface of the leaf, extends the full length of the gall. This species resembles very closely the gall produced by Cecidomyia majalis Bass. The general structure is shown in Fig. 7.

Dimensions: — Length along line of attachment to midrib, 10-12 mm. ; Width, 4-5 mm.

In the part of the leaf blade that forms the gall all resemblance to the normal mesophyll has disappeared. A compact mass of tissue has taken its place, the cells of which are much larger than normal mesophyll cells. Towards the interior of the gall the cells become smaller and richer in protoplasmic contents. The upper epidermis forming the interior of the gall remains practically normal, except that it produces longer and more abundant trichomes than when unstimulated. These trichomes are usually three cells in length. A cross section of this gall shows two small groups of cells with porous laminated sclerenchymatous walls, one of which is situated near the midrib and the other exactly op- posite on the other side of the gall opening. Thus each side of the gall aperture is bordered by a band of sclerified cells, as shown in the trans- verse section of Fig. 8.

Asiphum pseudobyrsum (Walsh)

Byrsocrypta pseudobyrsa Walsh, 1862:306.
Pemphigus pseudobyrsa, Oestlund, 1887:24.
Schizoneura populi; (misidentification), Gillette, 1908e:1.
Asiphum pseudobyrsa Gillette, 1914a:269; Hottes and Frison, 1931a:348; Gillette and Palmer, 1934: 217

Collections. In pseudo galls of leaves of Populus sargenti [deltoides]. Colorado: Grand Junction, Rocky Ford, La Porte, Denver, Longmont and Fort Collins. Fundatrices May 27 to June 18, alate viviparae June 16 to July 13; not common. Fundatrix living in same leaf as progeny but on underside of midrib with young locating on underside of branch veins. Second generation alate viviparae (fundatrigeniae) all leave the tree, probably for an unknown summer host.

Pachypappa pseudobyrsa (Walsh)

The fundatrix is wax-dusted, yellowish olive green with a blackish head; BL 4.0-4.7 mm. Its feeding causes a small blister-like swelling in the centre of the underside of the leaf near the mid-rib (see influentialpoints.com/Gallery). Its numerous progeny spread out in May-July along the main veins, developing into dusky-dark alatae, BL c. 3.5 mm. On Populus spp. (deltoides, fremontii, tremuloides) in eastern North America, where it is widely distributed, and also in Colorado (Palmer 1952, as Asiphum). The life cycle is unknown; the alatae presumably migrate to an unknown secondary host, although Smith (1974a) thought that it might be monoecious.

Pachypappa pseudobyrsa (Walsh, 1863)

Feeding by the stem mother induces a pocket-like pseudogall adjacent to the midrib of the leaf blade (Fig. 6). The gall projects up from the upper leaf surface, opening on the lower leaf surface. The gall is too small to contain the apterae, which crawl out to feed on the secondary leaf veins on the underside of the leaf. This feeding results in the lower leaf surface becoming coated with a powdery white wax formed by the apterae. Feeding also causes the two sides of the lower leaf surface to gradually bend toward one another to become almost parallel and form a purse-like pseudogall (Fig. 7). Galls are light green but occasionally have a tinge of red along the midvein of the leaf. Each gall may produce an average of 625 alatae (Alleyne and Morrison 1977). The species has also been referenced in the literature as Asiphum pseudobyrsum (Palmer 1952; Alleyne and Morrison 1977) and Pachypappa pseudobursa (Floate and Whitham 1993).

The primary host is P deltoides (Palmer 1952; Alleyne and Morrison 1977; Floate and Whitham 1993). Alatae are found in galls in mid-summer and presumably colonize unknown secondary hosts. This aphid has wide geographical distribution, with populations locally concentrated on individual trees.

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.