Galls found on the upper half of the stems of H. divaricatus, appearing like swellings of the stem; symmetrical, varying from ovate to spindle form; the long diameter of the gall in the axis of the stem of the plant; color the same as the stem. Walls of the gall are woody, hard, and about 1mm thick. The interior is filled with a soft, pith-like substance through which the larvae tunnel and on which they feed. Each gall contains 1 to 10 larvae.

Spindleform stem galls on Helianthus divaricatus

Tapered stem swellings...
N. thurstoni (Brodie). This species is probably univoltine. Hosts: H. divaricatus and H. spp. Distr.: widespread in North America.
...Two undescribed species other than N. thurstoni are known [from Helianthus spp. hosts] from larvae with distinctly different spatulae.