Euura S. ovum Walsh.

"On Salix cordata [eriocephala]. An oval or roundish, sessile, monothalamous swelling, .30 to .50 inch long, placed lengthways on the side of small twigs, green wherever it is smooth, but mostly covered with shallow longitudinal cracks and irregular rough scales which are pale opaque brown. Its internal substance fleshy in the summer like that of an apple, but with transverse internal fibres. When ripe in the autumn filled with reddish-brown spongy matter, with close-set transverse internal fissures at right angles to the axis of the twig. On cutting down to the twig at any time a longitudinal slit about .20 inch long becomes plainly visible." — Walsh .

As already noted the host of this gall in this locality is Salix humilis, it remains to be determined whether there are two distinct species of producers or one species with two hosts [Zinovjev and Smith imply this is more likely Euura salicisovulum]. Walsh's description of the gall on Salix cordata corresponds to the form occurring here on S. humilis.

The ovipositor of the producer has in this case made a longitudinal cut in the stem. A transverse section at the place where the gall is located shows that this wound extends in from the epidermis to the boundary of the pith. The activity of the young tissues, abnormally stimulated, soon fill this fissure with a mass of small, angular parenchyma. The rapid division of these cells forces the exposed edges of the cortex and central cylinder apart so as to form a wedge-shaped opening which is filled up with the gall mass (Fig. 71). It should be stated that the newly formed cells originate mainly from the division of a cambium bordering the pith at the bottom of the fissure. But other tissues also respond to the stimulation initiated by the ovipositor of the insect. Thus a section of the stem at a short distance from the gall shows that the outlying cambium has become abnormally active and has produced a layer of bast nearly one-third thicker than that found in the normal stem. Likewise the activity of a cork-cambium layer has thrown off a strongly cuticularized epidermis present in the earlier developmental stages .

Euura ovum

Salix species. Mass. Oct. Ovoid, scurfy elevations on stem; single cell.

Cryptocampus ovum

Euura salicis-ovum
Euura ovum
Cryptocampus salicis-ovum

This monothalamous gall consists of a deformed bud the tip of which persists. The gall varies considerably in size and shape, sometimes nearly spherical, again elliptical or ovoid, and tapering. When mature the larval cell is surrounded by a red-brown spongy mass, containing fibers transverse to the stem. Rather common on willow, Salix sp. Insect remains as larva during winter. Some apparently pupate underground. Imago in April.

Euura ovum

Irregularly elongated, ovate, reddish brown, spongy twig gall, 10 to 20 mm long.

S ovum n. sp.

On Salix cordata [eriocephala]

An oval or roundish sessile monothalamous swelling, .30 — .50 inch long, placed lengthways on the side of small twigs, green wherever it is smooth, but mostly covered with shallow longitudinal cracks and irregular rough scales which are pale opaque brown. Its internal substance fleshy in the summer like that of an apple, but with trans- verse internal fibres. When ripe in the autumn, filled with reddish-brown spongy matter, with close-set transverse internal fissures at right angles to the axis of the twig. On cutting down to the twig at any time, a longitudinal slit about .20 inch long becomes plainly visible. Particular twigs on badly infested bushes sometimes have one of these galls about on every half inch of their length, and not placed in a regular row, but indiscriminately on any side of the twig. Abundant but local. Described from very numerous specimens.

Euura ovum

Salix
Twig galls

Irregularly elongate, ovate, reddish-brown, spongy twig gall, length 1/2 to 4/5 inch, spring, sawfly

Euura salicisovum

Valid name. — Euura salicisovum Walsh.

Host. — According to Walsh on "S. cordata.'' Its currently accepted name is Salix eriocephala Michaux (= cordata Muhlenberg not Michaux) (Argus 1997). The galls are "monothalomous, spongy, growing from the side of the twig." Galls obviously belonging to this species were common on S. eriocephala around Ithaca, NY, in 1997 (Fig. 10).

Notes. — For further notes, see also Euura salicisovulum Walsh.

Euura perturbans

Valid name. — Euura salicisovum Walsh (= Euura perturbans Walsh).

Notes. — Euura perturbans was synonymized by Marlatt (1896). We consider this a color variation and accept the previously proposed synonymy under E. salicisovum.