Wednesday, June 8, 2016

Perlesta from a small mountain stream -- check!

I don't hold out much hope that we'll be identifying Perlesta stoneflies to the level of species anytime soon.  But it's possible.  After listing 13 possible species in North Carolina, Beaty goes on to note "North Carolina has very high diversity of Perlesta, most of which are undescribed at this time.  At least five species from NC are currently being associated." Maybe we'll get lucky.

But since it's June -- Perlesta season -- I thought I might collect some of these nymphs from different streams/locations to see if there are differences that we can discern.  Different species of stoneflies tend to differ in observable features on the heads, pronota, and the abdominal terga.   First stop today, one of our small headwater streams in Sugar Hollow, which was loaded with them.  Some pix.

On the nymph at the very top of the page, we can see the features we need for ID: 1) there is a complete setal row on the occiput (back edge of the head) with irregular gaps (see Beaty, "The Plecoptera of North Carolina," p. 19.)

better yet, a microscope view

and 2) the abdomen has a speckled appearance from the dark intercalary setae on the terga.

It is worth noting, however, that those setae on this nymph are much less pronounced than they were on the nymph I found in Buck Mt. Creek on 5/28.  This one.

Different species?  Too early to tell, but I'll be looking closely at features like these.  (Also note that the terga on the nymphs found today have narrow, dark transverse bands on the anterior and posterior edges.)

Only took photos of one other Perlid today -- a fairly mature Eccoptura xanthenses.  Beautiful colors.


Rapidan in the morning.

Interesting note.  When Unzicker and McCaskill published their study of Plecoptera (pp. 5.1 - 5.50 in Aquatic Insects and Oligochaetes of North and South Carolina, 1982), they wrote the following on Perlesta: "Two species of Perlesta are known from North and South Carolina, P. frisoni Banks and P. placida (Hagen).  The nymph of P. placida has a conspicuously speckled abdomen.  The nymph of P. frisoni is unknown.  Frison (1935) recorded Perlesta nymphs from the Great Smoky Mountains National Park in Tennessee which had lightly speckled abdomens.  These nymphs should be labeled as Perlesta sp. until the status of P. frisoni has been determined." (p. 5.28) Perlesta study has come a long way.

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