Undescribed Sawfly Gall (Euura N.S.) on Salix serissima Fernald.

This gall is produced by the abnormal swelling of the petiole of the leaf. The leaves infected are those borne on the branchlets from which spring the pistillate catkins. In the majority of cases, the leaf that bears the gall is the one from the axil of which the peduncle of the catkin arises. The swelling is so close to the branchlet that after the leaves have fallen, the gall appears to have originated from it. This misleading appearance is due to the petiole of the leaf breaking just above the gall. The galls are cone-shaped with the apex towards the blade of the leaf. They are marked deeply by three or four grooves that meet at the tip.

Dimensions: — Height of gall 7-8 mm.; diameter at base 6-7 mm.

The anatomy of this gall presents a very compact tissue, owing to the cells being placed close together without intervening air spaces. The very much thickened cuticle of the epidermis is the greatest departure from the normal tissue. Of the three bundles of the normal petiole two are lacerated by the ovipositor of the insect, as shown in Figs. 69, 70. In the mature gall the halves of these two are found in four widely separated regions (Fig. 69), owing to the abundant production of tissue between them. Indeed practically all the abnormal tissue is produced from the undifferentiated cells stimulated by the cutting of the bundles.

Euura serissimae, new species

Toronto, Ontario, Canada. One female bred from galls made on the leaf petiole of Salix serissima, by A. C. Cosens.

Euura serissimae

Salix
Leaf galls

Conical, on petioles of branches producing pistillate catkins, on S. serissima, sawfly, spring

Euura serissimae

Host: Salix serissima