Page:Phylogeny of cynipid genera and biological characteristics.pdf/32

 The galls of this genus are by far the simplest known among the Cynipidæ. Indeed, several species make absolutely no gall and are merely pith-inhabiting insects. Aulacidea bicolor has long been known to be such a species, and I have found, on investigations of dead stems, several other species of the same sort, of which I have already described A. abdita. Without a single exception, the galls of this genus are simple, never consisting of more than swellings of stems, agglomerate or polythalamous, without separable or even distinct larval cells, and in no case is the gall separable from the plant. As we have shown in the discussion of galls, such simple galls are primitive and indicate primitive relationships of the insects. Very interesting proof of the simple nature of even the most developed of these Aulacidea galls is furnished by the galls of A. podagræ and A. tumida. In each case the insect may be found in stems which show no traces of galls, although definite deformations of the pith surround the larval cells inside the stem; while, at other times, the same species (I am satisfied as to the identity after examination of large series of the insects) will produce a swelling of the stem, making a more or less conspicuous gall. It may be that the state of the plant at the time the insect's egg is laid in it, or the physiological nature of the particular plant, due to its special environment, determines the extent of the hypertrophy. In either event, it seems that the gall-producing powers of the insect are not developed enough to insure the formation of a gall except under the most favorable circumstances, although other Cynipidæ, whenever they produce a gall at all, apparently always produce galls of a uniform pattern and of the same degree of complexity.

This (Aulacidea and most likely Aylax and other related genera) is the only group of the Cynipidæ in which the sexes of most of the species occur in about equal numbers. Our data on this point are quite meager but seem to warrant this conclusion. The reproduction is normal, sexual reproduction, which is certainly more primitive than the partially or strictly agamic reproduction of the rest of the family.

There is apparently no alternation of generations in this genus, such as occurs in most of the oak gall-producing cynipids. Nothing that I know of from observation of the American species would indicate that there is anything but normal reproduction in the group. Aulacidea nabali emerges late in May and the galls are mature in September, appearing however a couple of months before that. A. podagræ emerges in mid-June, and the galls are good-sized by August. A. tumida emerges in early June; A. annulata emerges in early June; and the galls must develop o, the plants before they have become mature, which date for