Diastrophus niger
Cinquefoil stem spindle gall wasp

Host: Dwarf cinquefoil (Potentilla canadensis).

Gall location: Usually on the stem, but occasionally extending onto the petiole.

Description: Similar in size and appearance to the cinquefoil petiole spindle gall wasp. Spindle-shaped, multiple-chambered swellings. Unlike the cinquefoil petiole spindle gall, the stem spindle gall is not usually curved. The two galls occur on different cinquefoil species, and the identity of the host plant is often necessary to distinguish between the two.

Range: This gall has most often been encountered in the Northeastern United States from Connecticut to south New Jersey, and almost certainly occurs in adjacent parts of Canada. Museum records indicate that this gall may be found as far south as Arkansas, but this requires further substantiation.

This gall wasp was originally described as two separate species, the other being Diastrophus minimus. They have since been synonymized, but previous work on cinquefoil gall wasps has been largely incomplete, and further research may call this synonymy into question. This gall has also been reported in association with tall cinquefoil (Drymocallis arguta), but such records likely represent a separate, undescribed species (see “unverified galls and hosts”).

Diastrophus niger Bassett, 1900

Feeds on: Induces galls on Potentilla canadensis L.

Distribution: United States: Connecticut, Massachussets, Minnesota, New Jersey, New York, Rhode Island

Diastrophus niger

Potentilla canadensis

Spindle-shaped enlargements of the stem containing a dozen or more cells not in a single row.

[Photo caption]
325-6 On Potentilla canadensis. The adults emerged the next spring Apr 15-May 1 (Chi); Apr 10-25 (DC).

I have had in hand for several years a few galls collected at Wood's Holl from Potentilla canadense, by Miss Cora H. Clarke. They differ greatly in form and size, but I did not think the variations were specific and placed them together in the breeding box. The smallest are round or oval, not larger than the smallest peppercorn, and contains not more than one or two larval cells; while the largest are an inch long and one-fourth of an inch in diameter, and involve the whole stem and contain a dozen or more larval cells. Were the insects identical the form of the galls would not suggest any specific difference. When the large galls include a joint of the plant the joint is enlarged with the rest, but auxillary buds are not affected. In this it differs from D. potentillae Bass., which affects buds only and whose galls are monothalamous.

Diastrophus niger Bassett

Diastrophus minimus BASSETT

Gall. (Plate XXIX, Figs. 4-13). On the stems, or midribs of the leaves of Potentilla canadensis. Monothalamous when single and polythalmous when in numbers. Round, oval or elongate, smooth swellings (Fig. 6) sometimes involving the whole stem. Sometimes in nodules, singly, (Fig. 11) or in numbers, especially when on the midribs (Figs. 13, 14). Green when fresh and brown and pithy when dry.

Habitat: New York; New Jersey; Connecticut; Rhode Island; Massachusetts.

This species will probably be found everywhere locally, within the distribution of its host plant (Potentilla canadensis), which is distributed from Canada to Georgia and to Minnesota and Indian Territory. Through the kindness of Miss Cora H. Clark I received a number of galls on the midribs of the leaves and upon the stems, from which I raised many examples of the adults of D. niger. D. minimus I cannot separate from D. niger. This was bred by Bassett from blister-like galls which he supposed to be distinct from the double or confluent galls of D. niger. The types of niger and minimus are in the American Museum of Natural History and the American Entomological Society.