Pontania pomum Walsh.

"On Salix cordata (and very rarely on S. discolor). A smooth, fleshy, sessile, globular or slightly oval, monothalamous gall, resembling a miniature apple, .30 to .55 inch in diameter, growing on one side of the midrib of a leaf, and extending to its edge or sometimes a little beyond it. The principal part of the gall generally projects from the under side of the leaf, and only about one-sixth of its volume from the upper side, although very rarely it is at most equally bisected by the plane of the leaf. Scarcely ever more than one gall on a leaf and very rarely two of them, more or less confluent so as to seem like one kidney-shaped gall. Ex- ternal colour greenish-yellow, generally with a rosy cheek like an apple especially on the upper surface and often with many dark little dots on its surface." — Walsh .

The ovipositor of the producer of this gall has been thrust laterally through the midrib of the leaf into the mesophyll. The wound has completely severed the bundle of the midrib, as seen in Fig. 76.

The full-grown gall presents an epidermis with a very thick cuticle. The remainder of the gall consists of a complex of thin-walled cells arranged so as to constitute a typical aeriferous tissue (Fig. 77). A similar arrangement of cells is not found in the normal leaf, the mesophyll of which consists of a fairly compact tissue. The vascular strands growing out from the wounded bundle form a complete ring around the gall, situated about half way between the epidermis and the centre.

I was successful in obtaining this gall at such an early stage that the egg membrane was still unbroken (Fig. 76). This phase shows that the epidermis, the palisade and the spongy parenchyma mutually take part in the gall production. Counting along a line passing through the centre, four of the cell layers are seen to have arisen from the lower epidermis and six from the upper, eight from the palisade and fifteen from the spongy parenchyma of the leaf. Hence it is noteworthy that the new tissues are not the product of a cambium but have been contributed to by every morphological region of the leaf. The cells that are produced at this stage are in rows generally in exact alignment with the cells from which they have arisen. They thus do not have the arrange- ment of the aeriferous tissue of later stages to which they give rise. The cuticle, so marked a feature of the older stages of the epidermis, is exceedingly thin. The epidermis bears trichomes springing from the bottoms of deep pits (Fig. 76). This condition has arisen through the circumstance that the primary epidermal cells from which hairs have grown out have not experienced the periclinal divisions participated in by their fellows and so have been left far below the general surface as shown in the text fig. below.

Nematus pomum

Willow. Mass. June. Rounded, yellowish on under side of leaf. Sawfly larva, single cell.

Pontania pomum

Nematus salicis-pomum
Nematus pomum

Hosts: Salix longifolia [interior]

Leaf-gall, spherical to spherical constricted, on lower surface, and projecting slightly through. 5-10 mm. diameter. Color ranging from light green to red, depending upon light relation. Minute cork-specks frequently present. Very common. July 1st.

Nematus pomum

Nematus salicis-pomum

Rounded, fleshy leaf-gall, about 1 cm in diameter. Green with rosy cheek. Appears early in the spring, matures by late July. Insect emerges the following April. Common on heart-leaved willow, Salix cordata.

Pontania pomum

Rounded or ovate, fleshy, yellowish green, usually rosy-cheeked gall, projected slightly on the upper surface, diamter 12 mm.

S pomum, n. sp.

On S cordata [eriocephala] (and very rarely on S discolor]

A smooth, fleshy, sessile, globular or slightly oval, monothalamous gall, re- sembling a miniature apple, .30 — .55 inch in diameter, growing on one side of the midrib of a leaf, and extending to its edge or sometimes a little beyond it. The principal part of the gall generally projects from the under side of the leaf, and only about 1-6th of its volume from the upper side, although very rarely it is almost equally bisected by the plane of the leaf. Scarcely ever more than one gall on a leaf, and very rarely two of them more or less confluent, so as to seem like one kidney-shaped gall. External color greenish-yellow, generally with a rosy cheek like an apple, especially on the upper surface, and often with many dark little dots on its surface. Internal color whitish. The above is the appearance presented July 31 when the gall is fully matured, but as early as May 24 it has nearly attained its full size, and has the rosy cheek very conspicuous. Abundant but rather local. Described from very numerous specimens. As to the occasional occurrence of this gall on S. discolor see under No. 21 bis. An analogous gall is formed in Europe on the leaves of various kinds of willows by Nematus gallicola Westw.

Pontania pomum

Salix
Leaf galls

Rounded, yellowish-green, rosy cheeked gall, diameter .5 inch, sawfly, spring

Pontania pomum

Host: Salix cordata [eriocephala]

Among the numerous sand ridges, referred to previously, are many streams and ponds of water. These are skirted, often for long stretches, by a screen of the heart-leaved willow. The majority of these host plants are always infested with this gall.

Range: Toronto, Ontario

Pontania pomum

Nematus salicis pomum
Nematus hospes
Pontania hospes

Gall. — (Frontispiece, fig. 4.) The gall S. pomum found on Salix cordata [per Zinovjev, this is eriocephala] and very rarely on S. discolor. A smooth, fleshy, sessile, globular, or slightly oval monothalamous gall, like a miniature apple, 0.30 to 0.55 inch diameter, growing on one side of the midrib of a leaf, and extending to its edge or beyond it. The principal part of the gall projects from the under side of the leaf; very rarely it is bisected by the leaf. Color greenish yellow, sometimes with a rosy cheek, especially the upper surface, and often with little dots. Fully mature July 31. An analogous gall is formed in Europe on various willows by Nematus gallicola Westw.

Range: IL

Eupontania salicispomum, new combination

Nematus salicispomum

Valid name. — Eupontania salicispomum (Walsh), new combination.

Host. — The galls are on Salix eriocephala Michaux (= S. cordata). A subsidiary host plant might be Salix discolor Muhlenberg. Walsh wrote about it as follows: "On S. cordata, (and very rarely on Salix discolor)"; he found galls of Nematus salicispisum and galls "so identical in appearance with S. pomum"' on the same bushes." "In both the above two cases a few discolor bushes were growing in the midst of very large numbers of S. cordata, the species on which S. pomum is normally found." These data on its host plant specificity seem to be reliable, but confirmation by rearing adults is needed.

The galls are roundish (apple-like), transected by the leaf blade with a large part of the gall visible from the upper side of the leaf, but the larger part of the gall is situated below leaf surface (illustrated by Zinovjev and Smith 1999: 361, fig. 2).

Nematus hospes

Valid name. — Eupontania salicispomum (Walsh) (= Nematus hospes Walsh).

Notes. — According to Walsh "absolutely undistinguishable from the normal type of the gall-making N. s. pomum.'' Marlatt (1896) synonymized N. hospes, and these species have always been treated as conspecific.

[Listed in photos but not in text]

Hosts: Salix eriocephala