Biology of the rose stem galler Diplolepis nodulosa (Hymenoptera: Cynipidae) and its associated component community in central Ontario

Diplolepis nodulosa (Beutenmuller) induces small, monothalamous, prosoplasmic galls in stem tissues of Rosa blanda Aiton. Adults and galls are redescribed and notes on distribution, host records, morphological variation, and a comparison with related species are presented. Galls are commonly attacked by the inquiline Periclistus pirata (Osten Sacken). Data on life history and mortality of inducers and inquilines, along with seasonal variation in gall density, were obtained from a study site near Sudbury, Ontario, in 1993 and 1994. Inquilines killed 55% of the inducer population in 1993 and 65% in 1994. The abundance and density of galls fluctuated over the 2 years; however, the proportion of galls modified by inquilines remained constant. Six species of parasitoids caused an additional 17% inducer mortality. Aprostocetus sp. was the dominant parasitoid of D. nodulosa, whereas the other five species were incidental. The assemblage of parasitoids associated with galls modified by P. pirata caused 13% inquiline mortality and include seven species, of which Eurytoma spp. and Caenacis sp. were dominant. The unique aspects of the D. nodulosa gall system are discussed.