Wednesday, June 10, 2015

A review: Common stonefies (Perlidae), genus Acroneuria

I thought I'd make myself useful, while I wait for a crummy summer cold to let go.  This is something I've been wanting to do for myself as well as anyone else who enjoys reading along.

"Common stoneflies" (family Perlidae), genus Acroneuria: what are the species we see?  Two comments before we begin.  1) Genus Acroneuria Perlids are the most common, "common" stoneflies we see in our streams, and 2) keep in mind that this is a genus that Beaty insists is badly in need of additional work and revision.

1. Acroneuria abnormis

(That's also abnormis in the photo at the top of the page.)  This is the most common Acroneuria species I've seen, and I think I've seen it in every stream that I've explored, from the very smallest headwater streams to sizeable rivers like the Rivanna.  Distinguishing features: distinct M-shaped pattern on head, no anal gills, and banded tergites -- anterior dark, posterior light.  Tolerance value: 2.1.

2. Acroneuria arenosa (could also be Acroneuria evoluta)

To date, this is a species I've only found in the Rivanna.  So, a "river" insect.  Distinguishing features: M-shaped pattern on head pale to absent (arenosa) or reduced to three dots (evoluta), terga uniformly brown, anal gills present.  Tolerance value: 2.4 (arenosa) or 1.7 (evoluta).

3. Acroneuria carolinensis

Thrives in clean, cold streams of "medium" size -- in my experience at least (upper Doyles, Rapidan, North Fork of the Moormans).  Distinguishing features: head with light M-shaped pattern, banded terga: anterior light, posterior dark, no anal gills present.  Tolerance value: 1.2.

4. Acroneuria internata (but nymph in photo might be a form of A. abnormis)

This is a species that I've only seen once: small mountain stream, Entry Run in Greene County.   The distinguishing feature is the banding of the abdominal terga: the light posterior bands are of uniform thickness.  (In this case, the light bands are nearly uniform.)  No tolerance value is listed for this species in the documents provided by North Carolina.

5. Acroneuria lycorias

Similar to A. carolinensis in appearance.  But, A. lycorias has anal gills, and the banding is fairly uniform with no medial markings.  Fairly common in Buck Mt. Creek.  Tolerance value: 2.1.

Beaty provides descriptions for three other species: filicis, frisoni, and perplexa.  These are species that I haven't seen.  All three appear to be relatively uncommon.  (Steven Beaty, "The Plecoptera of North Carolina, p. 14)

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