Diplolepis spinosa (Ashmead)

The first report of Diplolepis spinosa was in Florida (Ashmead 1897), where the species was named from the characteristics of the gall. Gillette (1890) provided the first description of D. spinosa females but under the name Rhodites multispinosus. Burks (1979) recognized R. multispinosus as a synonym of D. spinosa. Beutenmüller (1907) and Kinsey and Ayres (1922) provided a more detailed description (as D. multispinosus) and illustrated the galls, as did Shorthouse (1988, 1993).

Galls of D. spinosa are one of the most conspicuous galls on the grasslands. They are spherical or irregularly rounded and often the size of a golf ball (Fig. 40). They appear attached to the main stem but are formed from a leaf bud (Figs. 9–12). They are firmly attached to their hosts and often can be removed only with snips.

Galls of D. spinosa are found from eastern Ontario to the Okanagan Valley and northeastern British Columbia. They are found only on R. woodsii on the prairies and in British Columbia and only on R. blanda in Ontario. They are never found on R. acicularis. Galls are usually weakly spined to smooth on the spiny R. woodsii on the prairies but always heavily spined on the smooth-stemmed R. blanda in Ontario. They average about 23 mm in diameter in Ontario (Bagatto and Shorthouse 1994) and those on the prairies are similar.

Galls are multi-chambered (Fig. 41), with most chambers located in a cluster near the centre. Immature galls are yellowish-green, soft, and usually clothed with slender spines. Mature galls are reddish-brown or dull purple, hard, and woody. Galls on wild roses from central Ontario have an average of 16.5 larval chambers per gall (Bagatto and Shorthouse 1994). Those on the prairies and in British Columbia are likely the same.

Galls collected in the spring from southern Saskatchewan in the Great Sand Hills are used here to illustrate a typical component community. Commonly, 20–30% of the inhabitants associated with populations of this gall are inducers (Fig. 46L). Periclistus sp. make up about 21.3% of all inhabitants, whereas parasitoids form about 50% of all inhabitants. The most abundant parasitoid was Eurytoma sp. at 47.1% of all inhabitants.

- Joseph Shorthouse, KD Floate: (2010) Galls induced by cynipid wasps of the genus Diplolepis (Hymenoptera: Cynipidae) on the roses of Canada's grasslands^©