Galls among the flowers or modified flowers...
Gall ovoid, white-haired, larger than florets...Rhopalomyia spp.

Galls are sessile and widest at base, 4–7 mm long by 3–5 mm in diameter, one-celled, ovate, pointed at apex, and green with white down. Adults have been reared from the galls in fall. The three species listed are too incompletely known to determine whether they are synonyms. ...similar galls have been taken on an aster in Nebraska.

R. crassulina Cockerell. Host: A. crassulus. Distr.: Colorado.
R. gemmaria (Stebbins). Host: A. ericoides. Distr.: Massachusetts.
R. lateriflorae Felt. Host: A. lateriflorus. Distr.: Massachusetts and New York.

Aster ericoides.
Cecidomyia? gemmaria, n. s. Fig. 110.

The deformed bud of an aster constitutes this gall. It is one-celled, ovate, pointed and in some cases mucronate, green with a dense white pubescence. Length 4-7 mm., width 3-5 mm. Walls of the conical cell 1 mm. thick. Abundant on Aster ericoides. Collected by Dr. Geo. Dimmock, Aug. and Sept. 1908. Found in October in great abundance when it had turned dark gray.