Diplolepis triforma Shorthouse and Ritchie

Diplolepis triforma was first described from galls collected near Sudbury, Ontario (Shorthouse and Ritchie 1984). It was given this name because three types of galls can be induced by larvae from the same female. They are found on R. acicularis throughout the Aspen Parkland Ecoregion and R. woodsii on the prairies and in southern British Columbia. This species is found across southern Canada and the Yukon and is usually sparsely distributed.

Immature galls are green swellings at the base of the apical meristem and usually are covered with dense spines. Galls are initiated in the early spring. Mature galls are conspicuous, woody, and firmly attached to twigs. Most galls are pear-shaped without distal stem growth (Fig. 38). However, about one-quarter of the galls have some distal growth and a few are fusiform swellings of a twig distal to its base. The gall is multi-chambered and the chambers are close to the surface (Fig. 39). They remain on their hosts over the winter.

Wiebes-Rijks and Shorthouse (1992) provided data on the inhabitants associated with a large population of galls near Sudbury, Ontario, for which the most common parasitoids were Eurytoma spp, Pteromalus, Torymus sp., and Orthopelma sp. Periclistus are not associated with this gall.

Diplolepis triforma Shorthouse & Ritchie, 1984

Feeds on: Induces galls on Rosa acicularis Lindl.

Distribution: United States: Minnseota; Canada: Alberta, Manitoba, Ontario,Saskatchewan