Unfortunately, Johannsen didn't include Asindulum tenuipes in his 1910 publication. He lists three species, one of which (A. montanum) is considered valid in Evenhuis's catalog, and the other two are placed in Macrorrhyncha (M. coxalis and M. flava). I'm afraid that there is no good reference for distinguishing A. tenuipes from A. montanum.

I have therefore gone to the original description (Walker 1848), which gives the abdomen as "gray, somewhat paler on the hind border of each segment, and having a yellow stripe on each side". This doesn't seem to match the photograph. Johannsen (1910) says the first three abdominal segments of A. montanum are black, the rest yellow, so it matches this description more closely. I would hesitate to call it anything other than Asindulum sp. without reference to the type, though. There are undoubtedly more than two species in North America, and Walker was notoriously bad at describing species.