Diastrophus kincaidii

The Gall 

Mature galls on thimbleberry are abrupt swellings on the stem or petiole (Fig. 1). They are irregularly swollen or lumpy and glabrous. Their size and shape vary greatly depending on the number and precise location of cynipid larvae present in the gall. Larval cavities may be numerous and usually are situated closely together. The majority are located in the vascular zone but many extend into the pith and cortex as well. The tissue immediately surrounding each larval cavity is hard and woody as are the outer tissues of the gall but the tissue between cavities is loose and pithy. Each cavity is irregularly ovoid and about 2X3 mm in size. Gall development proceeds rapidly following oviposition by the adult female in the spring. First evidence is a slight swelling on a stem seven to ten days following egg deposition. The swelling is due to enlarge- ment of cortical, xylem and phloem cells. At this stage of development larval cavities are not yet formed and the eggs and first instar larvae are wedged between plant cells. In three to four weeks after oviposition larval cavities have developed and a gall is present as an abrupt and noticeable enlargement of the stem. The cavities are formed by a proliferation of parenchyma tissue that surrounds individual larvae. Xylem and phloem tissues of the gall are disrupted and only the uninfected portions of the stem have normal vascular tissue. The tissues of most galls show signs of woodiness by the end of summer and during the fall all become woody.

Life History 

Diastrophus kincaidii is a univoltine species. The adults are relatively short lived following emergence in the spring. During the summer D. kincaidii passes through five larval instars and its galls become noticeable on thimbleberry. A long diapause begins as a prepupa in the fall and is broken the following spring when pupation occurs within the gall. The seasonsal occurrence of the life stages of D. kincaidii is summarized in Figure 2.

BIOLOGY OF THE THIMBLEBERRY GALLMAKER DIASTROPHUS KINCAIDII (HYMENOPTERA: CYNIPIDAE)