Page:Phylogeny of cynipid genera and biological characteristics.pdf/34

 Gillettia Ashinead. This is the synonymy recognized by Beutenmüller (1910), and is practically that adopted by Kieffer (1910). The characters by which these various groups are separated seem hardly sufficient for drawing generic lines.

The radial cell throughout this genus is open, and in many cases the limiting veins are quite considerably reduced. This, without question, is more specialized than the closed cell of Aulacidea.

The first abscissa of the radius is usually arcuate, the more primitive condition, or may be slightly subangulate (as in Aylax glechomæ), which form of the vein is somewhat more specialized than the arcuate vein found in Aulacidea and the other species of Aylax.

Other indications of some specialization in the wing-venation are (1) the reduction of the veins bounding the areolet so that this cell is closed in most of the species of this genus, and (2) the lack of pigmentation and the fine form of the veins in practically every case, this condition appearing to result ultimately in the disappearance of the veins.

In most of the species the second segment covers only about onethird of the entire abdomen, a condition as primitive as that found in Aulacidea. But the dorsal extent of the plate in some of the species is somewhat greater, indicating greater specialization. In Aylax pisum (=A. stephatnotidis Ashmead) the plate equals two-thirds of the length of the abdomen, though it is still small in lateral extent.

The hosts of this genus are as varied as the hosts of Aulacidea, including plants of at least sixteen different genera of seven natural families. This is the more primitive trait in the choice of hosts, as we have pointed out before.

The galls produced by the insects of this genus vary greatly in comnplexity. Aylax rufus produces no gall at all, living in the pith of stems, in this respect resembling Aulacidea bicolor, A. abdita, and Phanacis centaureæ. Most of the species produce decided swellings of the part affected, which is either stem, leaf, seed-capsule, or bracts, but the gall remains an integral part of the plant, more so in some cases than in others. Still other species form galls which are more or less separable from the plant, e. g., A. kernei, A. salviæ, A. pisum, and occasionally A. glechomæ and A. latreillei, and this represents a more complex condition. A character which holds for most of the species of this group, and one which indicates a more complex condition than any found in any of the species of Aulacidea, is the formation of distinct, but still inseparable, larval cells. The galls of some of the species (those which are inseparable from the plant) are polythalamous and aggolmerate; the galls of