Diplolepis bicolor (Harris)

Diplolepis bicolor was first described from galls collected at an unidentified locality in the northeastern United States (Harris 1841). It has a wider distribution in southern Canada than D. polita, being found from British Columbia to Nova Scotia but not in Newfoundland. Earlier workers have recorded the gall from Calgary (Weld 1926) to Alabama (Thompson 1915).

Mature galls are spherical, averaging 7.0–11.0 mm in diameter. They usually occur in dense clusters averaging eight galls per cluster and are clothed with sharp, stiff spines (Fig. 18). Galls are induced on the adaxial surface of leaflets but usually grow in a dense mass firmly attached to the shoots. Galls often remain on the shoots over the winter. They occur on all three species of prairie roses but are most common on R. woodsii.

Galls are single-chambered (Fig. 19) with walls much thicker than those of D. polita. Immature galls are either leaf green, yellow, or bright red. Most galls turn yellowish-brown as they mature, although some are bright red until they dry. Eggs are deposited in early May on the adaxial surface of immature leaflets (Shorthouse et al. 2005). Periclistus-modified galls are larger than inducer-inhabited galls.

Because populations of D. bicolor galls are usually widely scattered, it is difficult to obtain sufficient numbers to assess the community. However, a large population of galls found about 25 km east of Saskatoon, Saskatchewan, provided this information. The galls were heavily attacked by Periclistus (Fig. 44B), which is always the most abundant inhabitant. About 59% of the immature galls were inhabited by Periclistus and about 28% of the mature galls by the end of the season (Table 5). Inquiline-modified galls contained an average of 9.3 chambers (Table 4). By fall, only 5.5% of the inhabitants were inducers (Fig. 44B), which is typical throughout the range of this species. Parasitoids constituted about 32% of the remaining inhabitants (Fig. 44B), the most common being Eurytoma sp. and Pteromalus sp. About 39% of the Eurytoma sp. exited in the current year (Table 3), as did some of the Torymus and Pteromalus.

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