Diplolepis bassetti (Beutenmüller)

Diplolepis bassetti was first described from galls collected near Corvallis, Oregon (Beutenmüller 1918). However, the gall illustrated by Beutenmüller is that of the European multi-chambered gall of D. rosae, whereas galls of D. bassetti are single-chambered. Because D. rosae is established in Oregon, this early report likely confused the two species. Kinsey (1922) provided a detailed description of the adults and recognized two subspecies. However, he also appears to have confused the galls of D. bassetti and D. rosae.

Diplolepis bassetti induces mossy, monothalamous galls (Figs. 28 and 29) on the adaxial surface of the leaflets of R. woodsii in open habitats in southern Alberta and Saskatchewan and in the Okanagan Valley of British Columbia. Diplolepis bassetti is also sparsely distributed across southern Alberta and southwestern Saskatchewan.

Galls are usually found in dense clusters. Their surface is covered with soft filamentous hairs (Fig. 29) that are green to red when immature, turning brown when mature. Galls are initiated in mid-summer. The chambers rarely coalesce and the individual galls can be easily separated. Galls average 4–5 mm in diameter. They commonly remain attached to the host plant throughout the winter.

Two large populations of mature galls collected in the spring were chosen to illustrate community composition. One collection was made on the flood plain of the Oldman River north of Coaldale at the same site as the D. ignota galls (Fig. 44E). The second was made from several large patches of roses from Kelowna to Osoyoos, British Columbia. No data were obtained on the seasonal changes of Periclistus attack, the number of Periclistus per modified gall, or the percentage of parasitoids exiting galls in the fall.

Inducers were by far the most abundant inhabitants (Fig. 44I) at the southern Alberta site. Galls here also had few Periclistus, representing 2.8% of the community. Only 19.6% of the remaining inhabitants were parasitoids, with the most abundant being Pteromalus (7.8%) and G. stigma (7.5%). In contrast, galls from southern British Columbia (Fig. 44J) had fewer inducers (16%) and Periclistus were much more abundant (28.4%). Parasitoids constituted 55.3% of the emergents, with the most abundant being Aprostocetus (46.9%) and Eurytoma (5.5%).

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