Cecidomyia Vitis pomum, new species
For the satisfaction of the scientific reader, we annex descriptions of the above gall and of its Iarva, drawn up from the Alton specimen.
Gall Vitis pomum.— A smooth, globular, fleshy, grass-green gall, 0.9 inch in diameter, attached by a rough base of about 0.4 inch in diameter, like the base of a hazelnut, to the cane of the grapevine. Its external surface with about eight or nine longitudinal striae, dividing it into eight or nine segments, like those of a watermelon. Internally fleshy and of the consistence of the hull of a walnut for one-eighth of its diameter; then a series of elongated cells, divided each into two cells by a regular series of transverse partitions, the lower tier about 0.2 inch, the upper tier about 0.3 inch long. From center of one cell to that of the adjoining cell is nearly 0.1 inch, and there are seven or eight cells side by side.
In No. 2, page 28, and No. 3, page 54, of the American Entomologist, we referred to a "vegetable phenom- enon" said to be found in Virginia, in the form of an apple-like growth from a grape-vine. The prevailing opinion in that State seemed to be, that it was a kind of hybrid fruit formed by the union of a grape blossom with an apple blossom. But we intimated our opinion at the time, that it was no fruit at ail, but simply a gall produced by some unknown species of gall gnat. We have since received specimens of what is uudoubtedly the same tiling, from two different sources, first from Mr. B. L. Kingsbury of Alton, Illinois, and second through the kindness of Mr. Stauffer, of Pennsylvania, from Thos. Moehan, the well known editor of the Gardeners' Monthly. Mr. Stauffer has also favored us with a good colored figure of one that he cut from the wild Frost Grape (Vitis cordifolia), August 9th, 1850, which agrees perfectly well with the two specimens in our pos- session. Hence, after carefully examining these specimens, we can now announce with certainty that this ''vegetable phenomenon"' is really what wo originally inferred it to be — namely, a gall- niadc by a gall gnat. Fig. 85 a, will give the reader a very good idea of this gall, and Fig. 85, b, of its internal structure, showing the larvae that inhabit its numerous cells, a single larva in a single cell. All the galls that we have hitherto been treating of, have been what are technically termed "monothalamous" or "one-celled" galls, inhabited by a single gall-making larva. But this, as will be seen at once, is a "polythalamous" or many-celled gall, inhabited by a great number of gall-making larvae.
As the fly that generates this gall will, in all probability, not make its appearance until next spring or summer, and as we have consequently had, as yet, no opportunity to breed it; it may be very reasonably asked, how we know for certain that it will turn out to be some kind of Gall- gnat ( Cecidomyia)? We answer that the larvae of all Gall-gnats are distinguishable at once from other larva? by a peculiar process known as the "breast-bone," and located on the lower surface of the first joint of the breast. (See Fig. 86, c.) Usually this "breast-bone" is of so dark a color that it can be readily seen, even in a very small larva, and its use apparently is to abrade the surface upon which the larva lives and there- by cause an abnormal flow of sap, which forms the food of the little insect that is thus working for its living. In Figure 8G, c, the head of the lar- va is shown protruded ; but all this group of larvae have the power of retracting the head within the body, so as to bring the "breast-bone" well into play. In shape, this organ differs greatly, being sometimes what we have called "clove-shaped," as in Fig. 86, c, sometimes Y-shaped, as with the larvae of the two Willow-galls figured above, and sometimes of other allied shapes. But in every case there are several sharp prongs in front. of it, adapted for wounding and piercing. As a general rule, allied gall-gnats inhabiting the same genus of plants have larvae with "breast- bones" of the same, or a very similar shape. For example, that of the larva to be next described is absolutely undistinguishable from that of our larva; and so is that of Ihe larva of the Pine-cone gall from that of the larva of the Cabbage-sprout gall.”
- BD Walsh, CV Riley: (1869) Galls and their architects©