In California, Gnorimoshema sublerraneum is univoltine ... The larvae cause large, nearly spherical to watermelon-shaped galls (17-27mm long, 12-16 mm diameter, Fig. 102) on stems of Asler chilensis [Symphyotrichum chilense] ... Galls are full sized by March or April, but those taken from the plant prior to late April contain immature larvae ... prepupal larvae remain in the galls until pupation in late summer. Typically, galls occurred 12-1 S cm or more above ground level ... When the stems dry in fall, the galls become woody and persist, sometimes for two or more seasons.

[see pg. 45 for photo]

"...occurs on both the East and West coasts, but has not been reported anywhere in between. In the East, it is known only from the type series reared in Massachusetts from main-stem galls on Aster ericoides L. at or near ground level. The finished adult exit of this galler is covered by intact plant epidermis. In the West, G. subterraneum galls occur on A. chilensis Nees, varying in height from ground level upward."