Pemphigus vagabundus Walsh.

Host Populus deltoides, Marsh.

All the leaf rudiments of the terminal bud appear to be concerned in the production of this gall. Yet it is in reality a large pouch-gall with its wall thrown into smaller secondary folds. The apex of the stem, from which the gall originates, is usually swollen to nearly twice its normal diameter. These galls often remain on the host plant until the next season's galls begin to appear. The cells composing this gall form a compact and fairly uniform tissue and a nutritive layer is not clearly differentiated. About one- third of the thickness of the gall wall, on the side next the larval chamber, however, is composed of cells that are somewhat larger than the remaining cells. The epidermal cells, lining the gall cavity, are elongated into short trichome-like structures. The phyllome origin of this gall is revealed by the presence of well defined stomata on its epidermis. These structures are numerous and appear to be quite normal. Glandular cells are plentifully distributed. Vascular strands pass irregularly throughout the wall of the gall.

Mordvilkoja vagabunda (Walsh)

Collections. In large complicated, convoluted, bladderlike leaf galls, com posed of crumpled leaves of a terminal bud on Populus sargenti [deltoides]. Colorado: Hugo, Longmont, Brighton, Kuner and Fort Collins. Wyoming: Laramie. Fundatrices May 2 to July 16 (still full of embryos and apparently in their prime), alate viviparae (fundatrigeniae) July 10 to 15 (gall still containing numerous young), alate sexuparae and sexuales (dead in dry galls from a previous year) Aug. 19; rare though common and abundant at times in localities.

Mordwilkoja vogabunda (Walsh)

Gall on Populus sargentii [deltoides] formed from terminal bud, convoluted, bladder-like

The largest and most unusual gall on poplar in southern Alberta is caused by M. vagabunda. The primary host in the area is Populus sargentii.

The gall caused by this species is usually large and conspicuous. The feeding of the fundatrix on the terminal bud results in the formation of a bladder-like gall. Fig. 9 shows the early stage of one of these galls and Fig. 10 the fully developed, convoluted gall. In autumn the galls do not fall but turn woody and remain on the tree the following year. Distribution of M. vagabunda in Alberta is as follows: 1930, southern Alberta, Populus species (MacNay, C. G. (in litt.)); 1948, Rocky Mountain House (Strickland, 1953); 1955, Grantham, Populus sargentii; 1957, Turin.

Mordwilkoja vagabunda

The stem mother attacks the terminal bud of shoots to form a hollow, convoluted, bladder-shaped structure (Figs. 4 and 5). This structure apparently represents a cluster of galls, with each gall induced from a single leaf (Gillette 1914). Large clusters may reach diameters of 80-95 mm and attain a thickness of about 50-60 mm (Gillette 1914). Galls in southern Alberta produce an average of 637 (range: 98-2,040) alatae, with emergence beginning in mid- to late July and being 90% complete by August 5 (Harper 1959b).

The primary host is P deltoides, on which empty galls are often retained during winter months (Palmer 1952; Harper 1959a). Secondary hosts have not been reported. The author has seen one case in Montana of this aphid on what appeared to be a hybrid between P deltoides and P angustifolia. The aphid can be common on individual trees, but its distribution seems to be highly localized (Gillette 1914; KF, pers. obs.).

Pemphigus vagabundus

Byrsocrypta vagabunda

Populus deltoides

A deformation of the terminal bud with the leaves so changed as to lose all appearance of leaves, each becoming bag-like, sonic like cock's combs. Yellow-green, becoming nearly black in winter. Persistent. Very common. On poplar, Populus deltoides.

Morwilkoja vagabunda

Irregularly folded, convolute deformed leaves, diameter 2 inches, aphid, summer

Mordwilkoja vagabunda [Russo's photo seems to depict Aceria dispar, not Mordwilkoja. No observations of M vagabunda have been uploaded to iNaturalist west of Wyoming.]
[Page 60]

These convoluted, bladderlike leaf galls occur on nearly all cottonwoods.

Range: throughout much of the US and especially from the Rocky Mountains to the West Coast.

Mordwilkoja vagabunda Walsh.

Byrsocrypta vagabunda
Pemphigus vagabundus
Pemphigus oestlundi n. sp., Cockerell, Ent. News, p. 34, 1906.
Mordivilkoja oestlundi

The galls of this louse at the terminal buds of cotton- wood twigs have occurred in greater or less abundance in at least one limited locality near Fort Collins, Colorado, for the past fifteen or more years. The section referred to is mostly rather low, moist land, along the course of an irrigating ditch and near the river. It seems strange that the galls should not have become more generally distributed unless the alternate host is largely limited to the area mentioned. I am assuming that there is an alternate host for the reason that the lice all become winged and leave the galls rather early in the summer. Most of them are gone by August 1st here. The Galls, Figures IS, 19 and 20. When growing, the galls are as green in color as the Cottonwood leaves, and are, in fact, a transformed leaf in each case. On the inside of the green gall the main veins of the leaf are very prominent. Apparently these galls differ from others produced by Aphids by not having any opening to the exterior during their growth, but Mr. L. C. Bragg has discovered a small brown scale (Figure IS A, and 20, b) at the base of the gall, which seems to be the apex of a folded leaf, beneath which is an opening to the interior and through which the blade of a pen- knife may be passed without cutting any tissue. This opening is so narrow that the lice do not escape by it. About the time that fully matured winged lice are developed in a gall (about July 10th to loth, at Fort Collins), little star-shaped mouths (Figures IS and 19, o) appear at the apices of the more prominent lobes thru which the alate lice escape. Many of them appear on a single gall as shown in Figure 18. The galls nearly always are from terminal buds, and whether one or more of the leaves form a single gall I have no certain knowledge, but apparently it is one in each case. Large galls measure as much as SO to 95 mm. in greatest diameter, and about 50 to 60 in the greatest thickness.

*Professor Oestlund, in his Aphididae of Minnesota, p. 22, states that Walsh's vagabundus is evidently something different from the louse that has since been known to be associated with the coxcomb gall. To be sure, September is late to take the migrants from these galls, and the measurements given by Walsh are too large for this species. But he evidently had a louse belonging to the Genus Pemphigus, as then understood, and in the Walsh-Riley paper published in Vol. I, of American Etomologist, page 107, the vagabond gall was figured, and both the winged lice and the apterous stem mothers from the galls mentioned. As Walsh at that time considered the winged lice from these galls the same as what he had described as B. vagabunda, it seems to me best to abide by his identification of his own species, and especially as we do not know any other species to which to refer his original description, which is quite inadequate for its identification anyway. I am therefore retaining the name vagabunda.