Stem miner (Lepidoptera) in Ageratina

I located multiple examples of this miner in late August through mid-October, after the larvae had vacated the plant material. One mine I found in mid-July was also apparently vacant. In some cases, the externally visible linear stem mine was bound between two adjacent nodes of the stem, and it wound up and down along the length of the internode, crisscrossing and overlapping itself so as to effectively create a blotch mine in which most of the internode assumed a brownish discoloration. Close examination of the mine revealed a narrow, broken central frass line appearing like a string of dots and dashes. In at least two other examples, the mine wandered across multiple internodes, with only a portion of the surface tissue of each internode affected.

I have observed the distinctive pattern of brownish stem mining bound between two nodes on other plants, including leaf-cup (Asteraceae: Polymnia canadensis) and Culver's root (Plantaginaceae: Veronicastrum virginicum). An early-stage stem mine on the former host, which did not exhibit the pattern of being restricted between two nodes (perhaps because the mine was still in the beginning stages), contained a Lepidoptera larva that appeared to belong to the family Gracillariidae. In addition, one of the Veronicastrum mines contained a Lepidoptera head capsule that was superficially consistent with the family Gracillariidae. Given this fact along with certain characteristics of the white snakeroot mines, such as their very shallow penetration into the stem tissue and the occurence of a central frass line, I propose that the white snakeroot miner is also a gracillariid, but this has yet to be confirmed. Since I haven't observed any bark flaps or other signs of pupae in the white snakeroot mines, I believe pupation is off the plant or at least not within the mine.

See also: Ageratina stem insects compilation