Phylloxera symmetrica

Hosts: Carya pallida, tomentosa, tomentosa x pallida, texana

Leaf gall: pear [shaped]

Round and flat above; some can be slightly sunken below leaf surface or slightly convex; a depression in center; concolorous with leaf tissue, crimson, light green, or yellow; diameter 2.0–8.0 mm; below more convex and conical, globular, or pear shaped; base with or without constriction; pubescent; crimson, light green, yellow, or white. Opening below surrounded by 4–8 short pubescent bracts.

Range: AL, AR, DE, MS, OK, TN, WV

Phylloxera symmetrica Pergande

Galls on leaves of Carya tomentosa and other Carya spp. are variable; typical form is circular and almost flat above leaf, protruding as a thick-walled pale cone below leaf, basal diam. 2-5 mm. Alatae (BL 0.9-1.2 mm, with orange abdomen) emerge in late May-early June through a small opening in the apex of the cone, after which the galls become dry and brown. In vicinity of Washington D.C., USA. Life cycle is unknown. Pergande (1904) described variants from the typical form of gall ("vasculosa" and "purpurea") differing in colour, size and shape, which he considered to be due to differences in hatching time of the fundatrices and developmental stage of the leaf at onset of feeding.

Phylloxera symmetrica

Carya sp.
Conical or globose leaf galls with distinct orifice and containing aphids
Gall medium, walls fleshy, quite flat above, usually with a more or less distinct median depression, prominent and conical beneath, not constricted at the base, the nipple distinct, surrounded by short bracts, diameter 2.5 mm, height 3 to 4 mm.

Phylloxera symmetrica n. sp., Pergande.

This species, as far as its gall is concerned, appears to be closely related to, if not identical with. Ph. conifera Shimer, but as his description, both of the gall and its architect, is rather vague, brief and general in characterization, so much so as to apply equally as well to many others, it is deemed more expedient to describe it as new.

This gall has been noticed on young trees of Hicoria (Carya) tomentosa and some other species, in the neighborhood of Washington, for quite a number of years and appears to be slowly but gradually increasing.

Judging from the appearance of the galls alone, one is tempted to divide them into two or perhaps three distinct species, with regard to shape, size and color. A careful study, however, and comparison of the migratory forms of their architects, have conclusively convinced me that the different forms of these galls are nothing else but varieties of one species, depending, as it appears, on the earlier or later settling of the young lice, and the there- with connected more or less advanced stage of development of the young leaves. There can be no doubt that the larger and more brilliantly colored galls are the product of such of the young lice of this species which hatched in advance of the bulk of the same brood, just at the time when the development of the leaves was most rapid and the circulation of the sap most vigorous. To enable the future student, therefore, to recognize these different forms more readily, it is deemed expedient to figure each form of gall and to give each of them a variety name. All these forms are usually, at least in this locality, met with at about the same time and upon the same trees, though the two largest or more brilliantly colored galls are much scarcer than those of the typical form. As a rule, there is generally but a single gall on a leaflet, though occasionally two, or even as many as five or six, and in one instance even as many as twelve were observed upon a single leaflet, all crowded together near the base of the leaf, and more or less confluent. If there be more than one on a leaf, it will be observed that generally most of them are dwarfed, whilst but one or two have attained their full size.

At what date the young stem-mother settles down has not been ascertained, though it must be at the time when the young leaves begin to unfold, at about the middle or latter part of April, for it was observed that by the 20th of May many contained already pupae, and a few even some winged insects, whilst others contained only eggs and larvae. By the 15th or 20th of June most of the galls are empty and by the end of the month all inmates have left and the galls become dry and shrivelled.

Phylloxera symmetrica n. sp., Pergande. TYPICAL FORM.

This gall forms always on the under side of the . leaf ; it is quite flat on the upper side, or slightly convex, occasionally somewhat depressed at the middle, circular, with its margin generally more or less deeply sunken below the plane of the leaf and generally concolorous with the upper side, or of a somewhat darker shade. On the under side, however, it is quite prominent and regularly conical in shape, with an opening at the tip, which, however, is tightly closed till the time arrives for the migrants to leave. At this time the apex commences to split into 4-8, more or less slender, backward-curved bracts or filaments, surrounding a more or less circular opening. The color of the lower side of the galls is either that of the leaf or somewhat paler, though rather darkest towards the apex, and their surface covered rather sparsely with the peculiar hairs and pellets of resin so characteristic of the under side of the leaves, becoming more dense towards the apex. The walls of this gall are rather stout and of a dense and firm texture, increasing in thickness toward the base. The transverse diameter above ranges between 2-5 mm and the vertical diameter from 3-4 mm. After the insects have left, the galls gradually dry up, become brown, lose their shape and disappear at last almost completely.

In this connection it will be interesting to record here what appears to be a second crop of galls of probably the same species, though it is quite possible that later observations may prove this to be distinct.

On the 29th of July, 1883, while examining a solitary young hickory tree near the fair-ground, in the District of Columbia, standing at a distance of between 20-50 feet from the nearest trees of its own kind, it was observed that considerable numbers of young galls had formed on the uppermost and youngest leaves, which, to all appearance, could scarcely be older than, perhaps, two or at most three weeks. A further examination of the older leaves proved that they had been infested quite profusely by galls of the species under consideration, all of which were empty and more or less dried up, though a few were still on the upper side ; no galls of any other species could be detected on any of the leaves. Notwithstanding this fact, it is still possible that these new galls were the product of some other species, the winged form of which may have migrated there from some distance. These newly formed galls were smaller and also quite different in appearance. Their upper surface is also scarcely elevated above the plane of the leaf, with the centre quite distinctly depressed. This depression is reddish or pink and is generally encircled by a pale yellowish-green ring, the under side is more prominent, though by no means conical, and somewhat paler than above. All contained, besides the females, numerous eggs and also a few larvae. The female is yellow with the eyes black, the larva pale yellow with reddish eyes; the eggs are colorless, the more mature ones faintly yellowish.

Var. A. Phylloxera vasculosa Pergande.

This variety is more striking in appearance and much larger than the more common or typical form. It grows also on the under side of the leaves, but is rather scarce, there being not more than from one to perhaps twelve or a few more upon a tree. Its upper surface is very much like that of the typical form, though it is often considerably sunken below the plane of the leaf and is of very much the same color. The galls proper, on the under side, are very much of the shape of a vase or urn. They are more or less constricted at base, the sides rounded and of a pear- or more or less globular form. The opening at tip, which is closed while the galls are immature, opens at maturity into bracts, similar to those of the typical form, whereby a more or less distinct neck is produced. The color of the galls is pale green, or sometimes almost white or pale yellowish, the surface being quite pubescent. Their diameter across the widest part ranges generally between 5-8 mm, and their vertical diameter between 4-10 mm.

Var. B. Phylloxera purpurea Pergande.

This form or variety is in shape between the typical form and var. A. It is of about the same size or somewhat larger than the first. Its base is constricted and the remaining part beyond it quite conical, with the opening completely closed. The upper side is quite flat, somewhat sunken beneath the plane of the leaf and often most beautifully red, yellowish or paler than the leaf. On the lower side the galls are either pale green or whitish and the surface covered more or less densely with pale pubescence.