Page:Life histories of American Cynipidæ.pdf/12

 .—In the Linnæan collections and most likely lost.

.—Europe: throughout. Asia: western. North America: Canada (Toronto, Quebec) and New England to Georgia, west to Michigan, Kansas, anid Colorado.

The gall of this species is one of the best known of the cynipid productions, being large and attractive and occurring most often on cultivated plants or on bushes escaped from cultivation. The species is evidently of European origin, probably having been imported into North America and other parts of the world on the sweet-briar. This is one of the four known instances of the importation of a cynipid species from one continent into another.

The gall is a curious modification of the young leaves. It is among the most specialized of the Rhodites galls. But what has been gained by the specialization is not altogether apparent, for the amount of parasitism of this species is great (at least 15%), and evidently the peculiar devices which complicate the gall are of no avail in keeping out parasitic insects.

The galls of rosæ appear as early as June 5 (Adler, 1877), about three weeks after the eggs are laid; these galls are well grown in late July and mature by September. The insects overwinter as larva and pupate only a few days before their emergence from the gall. The adults emerge from April 27 to July 9. This is a wider range of dates of emiergence than is commonly found among the Cynipidæ and, unlike practically all of the other gall-wasps, adults of this species will sometimes emerge from a single gall at two or more dates separated by a month or more, indicating a considerable range of differences between the eggs from a single parent. The adults oviposit within a few hours after emergence, but may live for four or five days before dying.

Males and females are sometimes produced in about equal abundance. From my first lot of material I bred six females and seven males, and Cameron reported (1889) a similar experience. But other galls will give no males at all, indicating a great variation in the eggs laid by different individuals. The final average gives between one and two per cent males, and the observations of several workers (Adler, 1888; Cameron, 1889; et a!.) confirm my experience in this respect. It is to be expected that under such conditions the females are often not fecundated but, nevertheless, the eggs of such individuals will grow parthenogenetically. This was very positively proved by Adler (1877), who secured galls from eggs he had observed to be laid in the plant. He conducted extensive experiments with this species; in four different years he obtained similar results, rearing three generations in direct succession. obtaining galls