Stem borer (Lepidoptera: Noctuidae) in Monarda

In late May 2025, while finishing a walk with my father, I found a Papaipema larva tunneling in a growing shoot of Monarda fistulosa just above a part of the very same stem that had recently been tunneled by a Pseudopostega larva (Lepidoptera: Opostegidae; record 0339). The Papaipema larva had established two round holes in the wall of the stem, an upper hole and a lower hole, through which it appeared to have been expelling frass. It had also left a small amount of loosely compacted frass in its tunnel just below the lower hole and just above the region tunneled by the Pseudopostega larva.

The area formerly inhabited by the Pseudopostega larva showed a semicircular exit slit in the wall of the stem, and inside there was a darkened disturbance to the stem interior, which was already beginning to fill in with callus tissue. The semicircular exit slit appeared slightly aged, suggesting it had been made anywhere from several days up to a week prior, and the Pseudopostega larva itself was absent.

The galleries of the two larvae were separated by a very short region of stem, about 5mm in length, consisting of relatively intact green tissue with some light brown discoloration.

I reared the Papaipema larva on potato. It pupated by August 19, and the adult emerged on September 13.