Page:Phylogeny of cynipid genera and biological characteristics.pdf/9

 Sonchus, and Lactuca; while Aylax hieracii is found not only on species of Hieracium, Linaria, and Cytisus, but also possibly in the galls on Triticum.

Within the Aulacini of today, however, some degree of specialization may be noted. Over a third of all the species of the tribe are confined to plants of the rosaceous genera Potentilla, Fragaria, and Rubus; thirteen of these species, i. e., all but four of those found on those plants, belong to the very distinct genus Diastrophus, and this comprises the whole of the genus as far as known. Here again is specialization developed as the group has become morphologically distinct, but in this case the choice of hosts has not reached the extreme of specialization, nor has the morphological differentiation become more than generic from the parent forms of Aulacini.

The only other apparent case of specialized hosts in the Aulacini is in the choice of many genera of the Compositæ; but there is little significance in this fact, for the Compositæ are so predominant among plants today, both in number of species and of individuals, especially among woody-stemmed plants which offer winter shelter to insects, that a due representation of the genera of this family would always have a dominance of numbers. Moreover, there is no restriction of any one or two of the genera of the Compositæ to any single genus of the Aulacini except in instances where the number of species concerned is too small to warrant conclusions.

This immediate data, considered independently, would indicate that the following arrangement shows the order of origin of the cynipid genera: