Internal feeder (Diptera: Chloropidae) in Carex

I observed larvae and plant damage of this fly in mid-May 2018. The larva feeds in the pseudoculm, a stemlike structure formed by the bases of overlapping leaf sheaths in a vegetative shoot of the host. It excavates a linear channel in the leaf tissue, which may become externally visible as the shoot elongates and the leaves grow. Mature larvae apparently finish their feeding within the base of the pseudoculm. The pupation location is unknown.

Larvae are whitish, with a black cephaloskeleton and a conspicuous pair of fleshy lobes on the terminal abdominal segment. Rogers et al. (1991) write, "Seemingly unique (apomorphic?) for the phytophagous Chloropinae are the fleshy lobes (stigmatophores) that project posteriorly from the caudal segment (...) Nowicki (1873) was the first to note these lobes and suggested that they were taxonomically significant. Similar lobes have not been found in any of the secondary invaders that have been investigated [in wetland sedges]. (...) The fleshy lobes vary in size, shape, and pigmentation and could prove useful in differentiating closely related species." For definitions and morphological descriptions of pseudoculms and vegetative shoots in the hostplant genus, see Reznicek and Catling (1986). Thanks to J. Carr for pointing out the Rogers et al. reference.