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”).

- Louis Nastasi, Charles Davis: (2022) Field Guide to the Herb and Bramble Gall Wasps of North America^©