Aphid Corrugations on Birch.

Betula lenta L.
Betula alba var. papyrifera (Marsh) Spach.

The primary folds in the leaf that form this gall run parallel to the main veins, with the latter as boundaries between them. Their crests are on the upper side of the leaf, while the hollows which form the larval chambers are on the under side. The primary folds are divided into secondary folds, and these again into depressions resembling minute Acarina dimple-galls. This complex arrangement is conditioned entirely by the veining of the leaf, since each fold, primary or secondary, is sup- ported along its edges by veins. The folding can be seen in Fig. 9. The anatomical characteristics of these galls show that the folding of the leaf has not entirely changed the structure of its normal mesophyll. Around the gall cavities the spongy parenchyma is nearly normal through- out and the palisade layer is recognizable in different places. The cells, however, are considerably larger than the cells of the normal mesophyll. The cells of the lower epidermis, that form the lining of the gall cavities, are well filled with food materials for the larvae. The supporting veins on each side of the fold send out branches that supply the gall with an adequate vascular system. Hormaphis hamamelidis Fitch and Hamamelistes spinosus Shimer, as worked out by Pergande,^° show that they inhabit alternately Betula nigra L. and HamameUs virginiana L. The galls on the birch leaves are produced by the fourth genera- tion of Hamamelistes spinosus Shimer. Pergande described them as "pseudo-galls or corrugations". The witch-hazel galls produced by the stem-mother of this species are plentiful in this locality, but Betula nigra L. is not found here. The Aphids have consequently been compelled to extend their list of food plants to include B. lenta L. and B. alba var. papyrifera Spach.

- A Cosens: (1912) A contribution to the morphology and biology of insect galls ^©

Reference: https://www.biodiversitylibrary.org/item/99818#page/19/mode/1up