Stem borer (Lepidoptera: Noctuidae) in Blephilia

I found a young larva tunneling in a wilted stem in mid-May, and another larva in a similarly wilted stem in late June. In the June example, the larva dwelled in the lowest reaches of the stem just above the roots, with a frass expulsion hole in the wall of the stem roughly 5 cm above ground level. There was definite sign of tunneling higher in the stem as well, but little or no frass accumulation; evidently the larva had expelled almost all of its frass through the aforementioned hole.

I was also able to locate a spent pupa in a dead stem of the host in winter, the adult moth having apparently emerged late in the previous growing season. In this case, the affected stem showed a conspicuous hole roughly 10 cm above ground level; another ~15 cm above this point, the stem had lodged due to the presence of a second hole; this was evidently where the adult moth had emerged.

The pupal exuviae of the moth were positioned facing upward in the stem, about ~3 cm above the first (lower) hole. A partial larval head capsule accompanied some frass right below the same hole. The stem above the pupal exuviae also showed extensive pith scraping indicative of larval feeding. However, there was no frass in the stem except for the very small quantity accompanying the head capsule right below the lower hole. This was consistent with the observations during the growing season that suggested this species expels most of its frass from the stem.

I did not rear any adults.