Rose Galls
These are the work of several species of insects, mostly Cynipidae of the genus Rhodites (which see). This genus, in Europe, includes six species, entirely confined to Rose-galls; and, in North America, it includes four species almost confined to them--only one (R. radicum) resorting to Raspberries and Brambles as well as to the Roses, on all of which it causes large, oblong swellings on the root. The insects are, in all cases, small, the European species being from 1/10in. to 1/6in. long; but the species of Cynipidae require an adept in their study to recognise them, as they are much alike.
The Galls on Roses formed by species of Rhodites in Europe are as follows: 1. Smooth round Galls, like small peas, on leaflets of Rosa canina and of R. rubiginosa (the Sweetbriar), formed by Rh. Eglanteriae. 2. Similar Galls on leaves of Rosa centifolia (the Cabbage Rose), formed by R. centifoliae. 3. Round Galls, like small peas, but bearing a few long, straight spines, on leaves of several kinds of Roses, formed by R. rosarum. 4. Galls on leaves and branches of Rosa canina, formed by R. Mayri. 5. Irregularly formed red Galls, usually in the leaves, but often in other young parts of Rosa spinosissima, less often on R. canina; these are usually smooth, bright red, and thick-walled; and often two or more are joined together, so as to form irregular masses. 6. By far the most conspicuous Gall on Roses is that known as the Bedeguar. It may reach a size of 2in. in diameter. It varies a good deal in form, though usually rounded; but the surface is always covered with long, branched, mossy green or red hairs. On cutting a Gall across the centre is found to be a mass of woody consistence, in which are numerous cells or spaces, each with a more or less distinct wall of its own. The outer cell can frequently be broken off from the mass. In each cell lives a white larva which in the cell becomes a pupa and finally emerges as a four-winged fly about 1/8in. or 1/6in. long, named R. Rosae. The insects are black, with the legs mostly red-brown or dark brown; and the abdomen of the female is red-brown, with the end black. Weather-beaten fragments of the Galls often remains attached to the twigs for two or three years. A small Midge (Cecidomyia Rosae) galls the leaflets of various Roses, causing them to swell and become fleshy. None of these various Galls can be regarded as really dangerous to cultivated Roses, and most of them, save those of R. centifoliae, are almost confined to wild Roses. Cutting off leaves and branches, as soon as the Galls appear on them, is quite a sufficient check to prevent their undue increase in any locality.