Among the Instars: Perlesta
Hey bug folks! This week I took a tangent into the order Plecoptera and the family Perlidae, which has the most species of all the stoneflies, including 84 species found in North America. Now usually this family is known for relatively large nymphs with bold black and yellow coloring, but there is a huge amount of variability in appearance. For this week, I’m looking at Perlesta, a genus slightly smaller in size and with 17 species in North America. Even as adults, identification can be challenging, and many of the nymphs are undescribed, so they are left at genus level.
Perlesta, a genus of the stonefly family Perlidae
Ecology of Perlesta
Ecologically, stoneflies are a fascinating group. They can live in all kinds of freshwater habitats, usually occurring in any habitat with flowing water. The youngest nymphs eat detritus and then transition to predation on small invertebrates as they get older. Perlesta are moderately tolerant of pollution with a tolerance value of 5 (out of 10) for the Upper Midwest. They prefer habitats with lots of dissolved oxygen, but beyond that, they are found in a wide variety of stream types. When they are found in sites with less oxygen, they can be seen performing a “push-up” motion to have more oxygenated water flowing over their gills.
Perlesta taxonomy
Taxonomic characteristics for the family include highly branched gills located where each of the legs attach to the thorax and no gills on the abdominal segments. The genus is identified by the presence of three ocelli, anal gills, an irregular row of spinules on the occiput, and a light-colored abdomen with dark stout setae, appearing “freckled.”
Sources
Stewart, K.W. and B.P. Stark. 1993. Nymphs of North American stonefly genera (Plecoptera). University of North Texas Press, Denton, Texas.
Hitchcock, S.W., 1974. Guide to the insects of Connecticut. VII. The Plecoptera or stoneflies of Connecticut. State Geological and Natural History Survey of Connecticut Bulletin 107.