Stem swelling...
Swelling woody, evenly tapered; larva in the enlarged pith...Lasioptera solidaginis Osten Sacken

The exterior surface of the gall has the same texture as the rest of the stem. These galls are found near the base of the plant, 5–10 cm above the soil surface. The pith is soft with elongate, vertical larval tunnels...Host: S. canadensis, S. rugosa.

[Note: Gagné uses a very wide sense of "S. canadensis" including at least S. altissima and S. gigantea.]

I am indebted to Mr. Edw. Norton for the communication of several specimens of this Lasioptera, reared by him in a box which contained a number of galls on the stalks of Solidago, all resembling more or less the common gall of Trypeta solidaginis Fitch. [= Eurosta solidaginis] By a careful examination of these galls and their contents I attempted to discover from which of them the Lasiopteræ had escaped. Although this attempt remained fruitless, and I did not find, as I had expected, any exuviae of the pupa of the midge, I will nevertheless communicate some facts, which resulted from my examination, and may be useful for future observers. I soon perceived that the galls could be separated into three groups...
[goes on to describe the heterogenous nature of the galls he received, which included some not made by Eurosta solidaginis.]
...
Does Lasioptera produce a gall for itself, very similar in appearance to the gall of Trypeta and therefore, perhaps overlooked by me, or taken out of the box, before it reached me? Or does it colonize the galls of Trypeta, after they have been abandoned by their original owner? Or else, before the escape of the latter, the larvæ of both species living in company? All three cases are not without precedent in the history of Cecidomyiæ.

But from a gall on the same plant, and also on the allied Compositous plant Vernonia fasciculata. which is externally like the Lepidopterous gall [probably here referring to the gall of Gnorimoschema gallaesolidaginis], but is internally filled with brown sponge and numerous cells, I have bred many specimens of Lasioptera solidaginis O. S., a minute Cecidomyidous fly. Whether this Dipteron is inquilinous in the Lepidopterous gall, or the Lepidopteron in the Dipterous gall, or whether the two galls are distinct and both the Dipteron and the Lepidopteron are gall-makers, I cannot say with any certainty ; but on mature consideration of all the facts now known to me, I incline to the last supposition.

But from a gall on the same plant [Solidago sp.], and also on the allied Compositous plant Vernonia fasciculata. which is externally like the Lepidopterous gall [probably here referring to the gall of Gnorimoschema gallaesolidaginis], but is internally filled with brown sponge and numerous cells, I have bred many specimens of Lasioptera solidaginis O. S., a minute Cecidomyidous fly. Whether this Dipteron is inquilinous in the Lepidopterous gall, or the Lepidopteron in the Dipterous gall, or whether the two galls are distinct and both the Dipteron and the Lepidopteron are gall-makers, I cannot say with any certainty ; but on mature consideration of all the facts now known to me, I incline to the last supposition.

But from a gall on the same plant [Solidago sp.], and also on the allied Compositous plant Vernonia fasciculata. which is externally like the Lepidopterous gall [probably here referring to the gall of Gnorimoschema gallaesolidaginis], but is internally filled with brown sponge and numerous cells, I have bred many specimens of Lasioptera solidaginis O. S., a minute Cecidomyidous fly. Whether this Dipteron is inquilinous in the Lepidopterous gall, or the Lepidopteron in the Dipterous gall, or whether the two galls are distinct and both the Dipteron and the Lepidopteron are gall-makers, I cannot say with any certainty ; but on mature consideration of all the facts now known to me, I incline to the last supposition.

This is a univoltine species which produces a stem swelling at the base of the stem. Numerous larvae live in the gall chamber where they overwinter.