Page:Phylogeny of cynipid genera and biological characteristics.pdf/40

 Adler (1880) proved by experimentally breeding for successive generations, that Rhodites rosæ, R. eglanteriæ, and R. spinossissimæ produce galls and adults in the second generation which entirely resemble the galls and adults of the parent generation, i. e., that there is no alternation of generations among these species such as occurs among the oak gall-makers. I have obtained a second generation of Rhodites ignotus which, similarly, is like the parent generation, and it is unlikely that alternation of generations occurs anywhere in the genus.

Summing our conclusions concerning the evolutionary position of Rhodites, we find that it shows primitive relationships in some respects but is more or less specialized in other ways. The closed radial cell of most of the species, the arcuate first abscissa of the radius of one species, and the simple galls of some species require that we derive the genus directly from some group as primitive as Aulacidea. However, the high specialization in the choice of host, the developed hypopygium, and the occurrence of agamy throughout the genus show a great degree of development beyond that attained by Autacidea. The variation in the degree of specialization of the wing-venation and of the gall-structure indicates a considerable evolution occurring within the group itself.

This includes Neuroterus Hartig, Spathegaster Hartig, Ameristus A. Förster, Manderstjernia Radoszkowski, and Dolichostrophus Ashmead.

In this group of oak gall-makers the radial cell is entirely or partially closed in six species, and in the remaining forty-eight species it is entirely open. This would indicate that the group, rather directly descended from the closed-cell genera Aulacidea or Rhodites, has had considerable evolution occurring within the genus itself.

The first abscissa of the radius shows considerable variation in Neuroterus, from a condition almost arcuate to a form very distinctly angulate with a slight projection into the radial cell. In no case, however, that I have examined is the vein as broadly and entirely arcuate as in the genus Aulacidea.

The second segment of the abdomen of species of Neuroterus is about one-half as long as the whole abdomen, being somewhat longer dorsally in the female but with a less extent laterally, so that the segment in this genus, though larger than in the Aulacini, is smaller than in the other oak gall-wasps. That is, there is closer relationship to the