Stem borer etc. (Lepidoptera: Tortricidae) in Artemisia

I discovered apparent tortricid larvae in small spindle-shaped galls on upper stems of white sage (A. ludoviciana) in late June and early July. By late July, in a collection of stems bearing these galls, one of the apparent gallmaker larvae had emerged from the gall and begun tunneling into the stem at a point several centimeters below the gall.

In spring, I found mature tortricid larvae in overwintered dead stems of the same host. The larvae had hollowed out significant portions of the stems, which resulted in accumulations of dry pellets of frass in the galleries. Photographs show one of these mature larvae inside a dead stem that also bore the remains of one of the spindle-shaped galls near its apex. A larva from this batch pupated in spring and the adult emerged in the final days of May, 2018.

Based on this evidence, I concluded that the gallmaker and the stem borer are the same species, and that the galls harbor young larvae for a short time, but then these larvae exit the galls, crawl down the stems, and bore into the lower portions of the stems, where they continue feeding and eventually overwinter. This conclusion is perhaps supported by Brown et al. (1983), who report E. benignatum as a "gall maker on stem[s]" of A. dranunculus (p. 224) and who also state that some larvae reared from A. vulgaris did not cause visible swelling in the stems.