This species was previously recorded from Antennaria plantaginifolia (L.) Hook. (Asteraceae) in Wisconsin and Maine; the host on which I found it in New York was one of the smaller-leaved pussytoes species, possibly A. neglecta Greene.

...I observed that the plantlets of Antennaria plantaginifolia covering a sloping pasture in an open wood near St. Francis, Milwaukee, had been so severely attacked by Cecidomyids as to have almost all their terminal buds converted into galls.
[GF note: This probably refers to a different Antennaria species, because A. plantaginifolia in the current sense (e.g. as followed by POWO) probably doesn't grow near Milwaukee. "A. plantaginifolia" in 1888 could have referred to any Antennaria species in the eastern United States.]
...
The galls of Asynapta antennariae are easily confounded at first sight with those of the Cecidomyia [Rhopalomyia antennariae] to which I have given the same specific name. More careful examination, however, soon reveals enough differences to permit of distinguishing the two species.
The Asynapta gall is more elongate, while the tips of the component leaves are scarcely recurved. The development of white trichomes is more regular, giving the gall a satiny appearance. The inner or upper surfaces of the leaves do not produce trichomes as in the other gall, but are smooth and shining, and are found to be covered with minute drops of moisture when the leaves are stripped asunder. The cells of the leaves, too, contain none of the red coloring matter, which gives the galls of Cecidomyia a reddish cast. Each gall contains only a single insect, which is not swathed in woolly trichomes but hollows out for itself a smooth cavity with hard and nut-like walls.

Imbricated, short-woolly leaf bud gall...
Leaves forming gall not recurved at tips...Asphondylia antennariae (Wheeler)

Galls are reportedly more elongate than those of R. antennariae, and each contains one larva in a hard, central cell...Host: A. plantaginifolia