We agree this appears to be a sign of a stem borer, though it's difficult to judge exactly which insect it is without destroying the plant's stem to dig-in and look for one. If there are dead stems from last year nearby, it might be a small native stem-nesting bee, in which case it can be left alone. Otherwise, it might be the larva of a moth (one species is aptly named Lily Borer), but once inside the stem there isn't anything that you can do to treat it unless you wanted to sacrifice that entire stem to trim it out. Since you might get to enjoy blooms before the stem potentially dies back from borer damage, we think it's worth just waiting to take that chance versus trimming it back before bloom as the larva won't be moving from one stem to another.

Miri