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).

Diplolepis polita (Ashmead, 1890)

Nomenclature: Rhodites polita Ashmead, 1890 | Rhodites occidentalis Beutenmüller, 1922

Feeds on: Induces galls on Rosa californica Cham. & Schltdl., R. woodsii Lindl., R.acicularis Lindl., and R. arkansana Porter

Distribution: United States: Alaska, California, Colorado; Canada: Alberta, BritishColumbia, Manitoba, Ontario, Québec, Saskatchewan, Yukon

Diplolepis polita

Rosa sp.
Leaf galls
A small round gall on Rosa californica from Marin Co CA, minutely spinulose without distinct spines. Occidentalis (Beut) with spines as long as diameter of gall (Fig 202) is a synonym.

Fig 202. Undetermined rose gall. Collected at Dunsmuir August 22. This may be polita whose type galls from Marin Co CA are similar, up to 6 mm in diameter but it cannot now be determined if its spines were glandular tipped.

Diplolepis polita

Diplolepis polita is also a common galler on wild roses from western Canada where it is found along the Pacific coast on R. nutkana to central Quebec on R. acicularis. Mature galls are spherical, spinulose, single chambered and appear in clusters on the adaxial surface of leaflets (Fig. 6). Galls are frequently so dense that their weight causes leaves to droop. Galls are found on numerous varieties of R. rugosa (Shorthouse 1994).

Diplolepis polita

Galls of D. polita (fig. 3) are monothalamous, spherical, 3.5 to 5.0 millimeters in diameter, clothed with weak spines and formed on the adaxial surface of leaflets. Immature galls are yellowish-green, but mature galls are often bright red. They usually occur in clusters with several galls per leaflet. They are found only on Rosa acicularis Lindl. in forested regions of Alta. and Sask. growing in partly shaded habitats. Walls of mature galls are thin (about 1 millimeter) and easily crushed with fingers. The larvae feed over the entire chamber surface. Adults removed from cold storage take an average of 26.8 days to emerge (fig. 9) and are present in the field in early May with the first galls present by about May 20. Periclistus take an average of 23.4 days to emerge after cold storage. Periclistus are found in about 71 percent of the galls by mid-season (table 1) and are the major source of inducer mortality. Galls are mature and on the ground by mid-August.