Page:Phylogeny of cynipid genera and biological characteristics.pdf/45

 not studied the life histories of any of the species. I have tried to breed the species for successive generations but, thus far, have not succeeded. Several of the species require two years or more for an insect to reach maturity and this makes the experimental study of these insects very difficult. All of the species, apparently, emerge in the winter. I have observed D. globulus ovipositing in the lateral buds of oaks but secured no galls from these buds. Whether a gall similar to that in which the parent insect matured would have resulted if the eggs had developed we cannot say positively.

Disholcaspis, then, is a genus which, in having an undeveloped second abdominal segment, shows what would appear to be a primitive character. But in wing-venation, restriction of the choice of host and of the part of the host affected, in the great complexity of gall-structure, and in completely agamic reproduction (in the one generation, at any rate), it shows great specialization, which is almost as great as that reached by any other genus of cynipids. It may be that the group is derived directly from the primitive oak-gall-producing Cynipidæ, becoming, however, very specialized. I cannot otherwise explain the persistance of the small abdominal plate. Knowledge of the life cycle of some of the species would throw considerable light on the question.

SUMMARY

The following are my conclusions which apply to the true gall-wasps:

1.—The closed radial cell of the wing is more primitive than the open cell; closed-cell genera or genera containing any species with the cell closed must be derived from closed-cell genera.

2.—The arcuate first abscissa of the radius is more primitive than the angulate vein showing a projection into the radial cell; the character of this vein is of generic importance and the extent of development toward the angulate vein indicates, in general, the extent of evolution of the genus.

3.—The size of the dorsal plate of the second abdominal segment is of generic significance; the smaller plate is more primitive; but this character among some Cynipini does not always show as great specialization as other characters in a genus, indicating diverse lines of evolution within the Cynipini.

4.—The primitive Cynipidæ were polyphagous; the restriction of Diastrophus mainly to Potentilla and Rubus, and the almost complete restriction of the Rhoditini to Rosa and of the Cynipini to Quercus show great specialization which occurred along three distinct lines of evolution.