Host plant: Lepidium sp.
Apparently this is the first image of a larva of this common moth species on BG. This critter matches the description by Munroe (1973, MONA fasc. 13.1B, p. 145): "The last stage is green. ... The subventral fold is narrowly whitish. There are dorsal segmental bands of a dull crimson color reaching the subventral fold laterally; the edges of these bands are irregular and project anteriorly at the spiracle." Munroe also mentions that "the larva feeds on peppergrass ... eating unripe seeds out of the flat pods and leaving two holes in the upper surface of each pod." This effect can be seen on a few of the pods in the lower part of the image.
At present, BG has about 150 images of adults and iNaturalist has over 1,000 images of the species; I can find no other images of larvae, but they are undoubtedly lurking in piles of unidentified caterpillars.
More on the story of the discovery of this caterpillar can be found on the iNaturalist upload and in this journal post.