Diplolepis polita

Diplolepis polita was first described from galls collected in the United States by Ashmead (1890). This species is now known to occur from the coast of British Columbia north to central Alaska and the Yukon, east to western Quebec, and from central Ontario north to James Bay. It is common throughout the Aspen Parkland Ecoregion from Alberta to Manitoba on roses in partially shaded areas at the edge of forests (Fig. 4).

Mature galls are spherical, averaging 3.5–4.5 mm in diameter, clothed with weak spines, and found on the adaxial (upper) surface of leaves (Fig. 16). They are single-chambered (Fig. 17) with thin walls and usually grow in clusters, several galls per leaflet. Galls are found both on the sucker shoot and on multi-year roses. Galls always abscise in late summer. Immature galls in shaded areas are usually greenish-yellow, whereas those growing in areas open to the sun are often bright red. All turn light brown when dry.

Galls of D. polita are found only on R. acicularis east of the Rockies, never on R. woodsii growing in open areas of the southern prairies. However, they are found on R. woodsii in more shaded areas in the Okanagan in British Columbia. A large population was found on R. arkansana near the top of the Cypress Hills in Alberta (Shorthouse 1991).

A large population of galls from within Prince Albert National Park in Saskatchewan illustrates the composition of a typical component community (Fig. 44A). Only 4% of the inhabitants were inducers by fall, 29% were Periclistus, and the rest (67%) were parasitoids. Periclistus (average of 5.4 per gall; Table 4) were commonly found in about 70% of all maturing galls and 12% of mature galls (Table 5). The most common parasitoids were Eurytoma sp. and Pteromalus sp. (Fig. 44A). About half of the Eurytoma sp. and half of the Torymus sp. matured and exited galls by the end of the season (Table 3).

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