Diplolepis ignota (Osten Sacken)

Diplolepis ignota was first described from galls collected at undisclosed locations in the eastern United States (Osten Sacken 1863). Beutenmüller (1907) and Kinsey (1920) provided descriptions of the adults. This species has been recorded in Minnesota (Olson 1964), the eastern United States (Beutenmüller 1907), and as far south as Florida (Thompson 1915). It is found in the Mixed Grassland Ecoregion across the driest regions of southern Alberta and Saskatchewan.

Galls are found on the abaxial surface of leaflets and are variable in shape and size. Single galls are spherical, but they usually coalesce to form irregularly rounded, often reniform masses (Fig. 24). Two or three masses commonly form in one large elongated cluster that causes host leaves to droop. Galls are single-chambered (Fig. 25), but when they coalesce, they appear multi-chambered. Single-chambered galls when mature average 6–9 mm in diameter. Reniform galls average 15–20 mm in length. Mature galls become hard and woody when they dry but are soft and spongy when wet. They have a smooth surface without spines or protuberances. Galls are initiated in early August. Mature galls are light tan and remain attached to their hosts.

Galls are found only on R. arkansana in Alberta and Saskatchewan, especially on those species growing sparsely on the flood plains in river valleys in areas without overgrowth or in open prairies without other shrubs. Beutenmüller (1907) and Kinsey (1920) reported galls on R. blanda, R. carolina, R. virginiana, and R. nitida in eastern North America.

Three populations of D. ignota galls are included here for an overview of the component communities. One population (Fig. 44E) was found on the flood plain of the Oldman River north of Coaldale, Alberta. Rosa arkansana here were growing among patches of R. woodsii on which galls of D. nebulosa and D. bassetti were common. The second site was a pure stand of R. arkansana about 2 km away on the level prairie above the flood plain (Fig. 44F) and was chosen to compare two communities near one another. The third site was an isolated patch of R. arkansana growing on native shortgrass prairie about 20 km north of Maple Creek, Saskatchewan. This circular patch of roses was about 50 m in diameter and most plants were galled. Galls at all three sites were collected in the spring and returned to the laboratory to emerge the adults.

Low numbers of inducers were present at the two Coaldale sites (Fig. 44E and F), but 23.5% of the inhabitants were inducers at the Maple Creek site (Fig. 44G). Few Periclistus were among the inhabitants at all three sites. Parasitoids constituted 75.8–92.5% of individuals recovered at each site. Aprostocetus was the most dominant parasitoid, followed by Eurytoma and Orthopelma. Communities at the two Oldman River sites were remarkably similar, whereas the Maple Creek site had more inducers. The reason for the differences could be that the Maple Creek site was more recently established and the parasitoids had yet to become established.

From a typical population of galls east of Saskatoon, Saskatchewan, 11.4% of galls in mid-season were inhabited by Periclistus and 5.8% by the end of the season (Table 5). The mean number of Periclistus larvae per gall was 2.9 (Table 4), with only 1.9% of the Eurytoma exiting in the year of gall induction (Table 3). Similar data were not obtained from the sites used for the communities summarized in Fig. 44.

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