Tuesday, November 27, 2012

Back to Uenoid species ID -- and a report from Sugar Hollow

I. Let me begin with the report.  I have not had very good luck in my recent stream visits: I haven't found a whole lot of insects, and I haven't found the insects I was hoping to find.   Last Wednesday (11/21) I went to the Rivanna at Crofton, looking for the Giant stoneflies that live in that river so I could check on the species ID.  I found nothing but large winter stoneflies (T. burksi/maura) and a few common stoneflies (genus Acroneuria) -- nothing to photograph.  On Friday (11/23) I tried the Rivanna at Darden Towe Park -- the exact same result, and the large winter nymphs were "dirty," in mudded up leaf packs.  That afternoon, I headed to Buck Mt. Creek, and you all know the results of that trip.

Yesterday, I decided to go to one of the small mountain streams in Sugar Hollow where I was sure I'd find a variety of small Perlodids -- I did not find a one, and again I did not see a lot of insects. But I did take a few photos.

1. The flatheaded mayfly, Maccaffertium merririvulanum -- tolerance value 0.5 -- the species that I've only found in these small mountain streams.  Identity is established by the pale "V" shapes on terga 5, and 7-9.

2. A fairly large fingernet caddisfly larva, genus Dolophilodes.  Genus ID is established by the asymmetrical (wavy) frontoclypeal apotome (front edge of the head).

3. Also visible in the photo above -- a freeliving caddisfly larva, Rhyacophila nigrita.  For the ID, note that the leading edge of the pronotum is darker than the rest of the pronotum.

4. And a Chloroperlid stonefly, genus Sweltsa.

I found other things of which I did not take any pictures: Giant stoneflies, big and small; small winter stoneflies, but nothing mature; common stoneflies, both Acroneuria and Eccoptura; and a few Peltoperlids (Roach-like stoneflies).  But I didn't see a single Perlodid, and the water was low, and the leaf packs aren't really forming.

II.  Now on to the question of Uenoid species ID.   The Uenoid case-maker (caddisfly larva) at the top of the page was found on 2/18/11 in Elk Run, a small tributary to Buck Mt. Creek.  The species is Neophylax oligius.

Let me tell you how I arrived at this species ID.  First, as I believe I mentioned last time, the caddisfly family Uenoidae consists of 5 genera: Farula, Neothremma, Sericostriata, Neophylax, and Oligophlebodes (see Glenn B. Wiggins, Larvae of the North American Caddisfly Genera Trichoptera), 2nd edition (Toronto: University of Toronto Press, 1996), pp. 413-415.)  The only genus that occurs in the East is Neophylax.  So, if you find a nice Uenoid case like the one at the top of the page -- with 3-4 large pebbles on each side of the case -- you not only know it's a Uenoid, you know it's a Neophylax Uenoid.  If you do not have the case, only the larva, you'll want to look for two things: 1) the leading edge of the mesonotum is "emarginated" (dented -- "anteromedial emargination"), in the shape of a "W," and 2) the ventral apotome is "T" shaped.

Steven Beaty lists a total of 10 species of Neophylax that might be found in North Carolina ("The Plecoptera of North Carolina," pp. 86-87).    However, his work group has never seen three of the larvae -- N. aniqua, N. atlanta, and N. kolodskii,  and two other species -- N. concinnus and N. toshioi -- have been found in parts of Virginia but not yet in North Carolina.  Of the rest, three species are said to be "common," the other two rare.  Common: N. consimilis, N. mitchelli, and N. oligius -- the "most common Neophylax in NC" (p. 87): uncommon: N. ornatus and N. fuscus.

The two most important characteristics used in establishing Neophylax species ID are 1) the presence or absence of ventral "clavate" gills on the first abdominal segment, and 2) the color of the head.  Let's look at the ventral side of the larva that lived in the case in the photo at the top of the page.

Clavate gills are gills that are wider at the tip than they are at the base (to me, they look like little balloons), and this larva clearly has them .  The front of the head is dark brown with a large, medial, yellow stripe.  Let me read from Beaty's descriptions:

N. oligius -- well developed clavate ventral gills on abdominal segment 1; yellow stripe on head, but varies, should be greater than 1/2 head length...underside of head usually testaceous [shell like].  Mountains and Piedmont. ... Most common Neophylax in NC.

I'd say that's what we've got.  And judging from the specimens that I've preserved over the years, I'm inclined to think that N. oligius is also the most common Neophylax in VA.  Almost every larva I have in my vial of Uenoids has the gills and has the yellow stripe on its head.

But, I have found additional species, some whose heads/faces are totally brown.  E.g. this one I found in South River on 1/4 at the start of this year:

and, the small Uenoid I found at Buck Mt. Creek on Friday had a brown head, and it did not have clavate gills.  (Only three of the possible species, by the way, do not have clavate gills: N. concinnus, N. toshioi, and N. fuscus.)

So, I have something fun to work on over the winter.  Can we identify all of our Uenoids to the level of species?  Stay tuned.

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