Stem and petiole borer (Diptera) in Aquilegia

In late August 2021, I noted a borer tunnel in the interior of a basal leaf petiole of the host. The tunnel was approximately 15mm long, brownish in color, with no significant solid frass accumulation. It appeared to originate beneath an externally visible oviposition hole in the outer wall of the petiole, the hole surrounded by a thin collar of whitish tissue and raised slightly above the level of the surrounding tissue. It was not clear if the tunnel was aborted or if it led into the crown or roots of the plant.

At the same time the following year, I found a somewhat similar tunnel in the interior of a stem near ground level. The tunnel walls were somewhat ragged, similar to dipteran tunnels from other hosts. An elongate, dessicated object in the tunnel could not be conclusively identified, but it appeared to consist partly of small discs that were reminiscent of the calcareous discs I have observed in the bodies of agromyzid larvae. For more on these discs, see Ellis (2024).

Finally, I observed tunneling consistent with Diptera in the very base of a overwintered dead stem of the host in early spring.

Together, these observations suggest a fly borer that conducts brief feeding in the lower part of a main stem or leaf petiole and then migrates to the roots, where it completes the bulk of its activities. Because no puparia have yet been found in stem interiors, I assume that pupation occurs in the roots or off the plant.