Diplolepis nodulosa (Beutenmüller)
Diplolepis nodulosa was first described from galls collected in the northeastern United States (Beutenmüller 1909). A detailed description of adults was provided by Brooks and Shorthouse (1997). Galls of D. nodulosa are tiny swellings at the tips of stems of R. woodsii and are barely perceptible (Fig. 34).
Mature galls are single-chambered, fusiform, and spineless (Fig. 34). They average 3.1 mm in diameter and are commonly circumscribed by a series of stunted leaflets. Galls are green when immature but frequently turn red when mature. Larvae are usually found in a vertical position within their chambers (Fig. 35).
Periclistus greatly enlarge inhabited galls (Fig. 36), making them highly visible and indicating that D. nodulosa is in the area. Galls modified by Periclistus (Figs. 36 and 37) are multi-chambered, spherical structures averaging 12 cm in diameter, with some galls being 20 mm in diameter. Galls found near Sudbury, Ontario, contained an average of 17 Periclistus per gall (maximum of 146) (Brooks and Shorthouse 1997) and prairie galls are likely similar. Immature Periclistus-modified galls are initially green but turn mottled red- brown in the fall and are gray-tan by the following spring.
A closely related species, D. inconspicuous Dailey and Campbell, has been found in California on R. californica (Dailey and Campbell 1973). Its galls are identical to those of D. nodulosa, but the adults are morphologically distinct (Brooks and Shorthouse 1997). Diplolepis inconspicuous is apparently restricted to the west coast of the United States, whereas D. nodulosa is found throughout eastern and midwestern North America (Shorthouse and Ritchie 1984), east to the north shore of Prince Edward Island, and west to British Columbia. It is found on R. blanda in Ontario, R. virginiana on Prince Edward Island, and R. woodsii in British Columbia, Alberta, and Saskatchewan.
For a large population of galls near Sudbury, Ontario, Periclistus killed 65% of the inducers and parasitoids killed an additional 17%. Communities of prairie galls are likely similar (Brooks and Shorthouse 1997).
