Cabin fever sets in -- time to get to a stream

The wind and cold couldn't stop me this morning.  With no warm weather in sight, I decided to brave it and check out a small stream in Sugar Hollow.

I was hoping to find two different things, and I found both.  That's one in the photo at the top of the page: the free-living caddisfly larva, Rhyacophila banksi complex.

I've found this species before in this stream, along with R. fuscula, R. nigrita, R. glaberrima and R. carolina.  This is the best stream I know of for finding Rhyacophilids.    This larva matches the description for the species R. banksi, but entomologists feel R. banksi can't be distinguished from a number of similar species.  Hence, "R. banksi complex" (which belongs to the R. invaria group).

On January 28 of last year, I posted a thorough review of how we arrive at this identification.  There's no need to go over that detail again.  But, two of the features that nail this down are

1) There is a single, large, ventral tooth on the anal claw,

and 2) the second segment of the maxillary palp is twice as long as the first.

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My second goal was to find one of those Isoperlas that I think might be I. kirchneri (see the entry of 1/25) -- and I was successful.

Whatever species it turns out to be -- I. montana, I. kirchneri, or something else -- this is the same nymph that I've found here in previous years: no "bars" or "stripes" behind the ecdysial suture.

Since I had none of these in my collection, I preserved it so I could see what the lacinia looked like.  But, nothing unusual there: same shape and make up that we normally see on most Isoperlas.

This was a young one.  Have to get back here in March and April to see one that's mature.

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The most common taxon today?  Not much question about it: the large winter stonefly, Taenionema atlanticum -- and this one was fairly mature.

The importance of laciniae in Perlodid stonefly genus ID: focus, Isoperlas

(Perlodid stonefly, genus Skwala.  Oregon, October, 2013.)

For those of you who, like me, like to work at the level of genus ID, with Perlodid stoneflies, one of the first things you need to examine is the laciniae ("teeth" used for tearing) of your nymph -- shape and constitution.  If you look at the keys -- Peckarsky's Freshwater Macroinvertebrates of Northeastern North America; Merritt, Cummins, and Berg, Aquatic Insects of North America --  you'll see that laciniae can differ markedly.

For example, each lacinia of the genus Remenus has only one tooth.

Diploperlas have two (apical and subapical).

The laciniae of Malirekus stones are more elaborate: two teeth, a knob with a tuft of setae, and dark clothing hairs along the base.

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In general, the shape and make-up of the lacinia can help us get to the level of genus when we're working through keys.  But Isoperla Perlodids can present a bit of a problem.   Here is the lacinia of Isoperla dicala which represents very well the general Isoperla description we find in the keys.

There is an apical tooth and a subapical tooth; the base is wider than the apex; below the subapical tooth, there are usually 4-6 spine-like setae with finer setae often continuing on to the base.  And, Isoperla laciniae are often medially constricted.

Here is the description we find in Merritt, Cummins and Berg, p. 332.

88' Apical lacinial tooth much shorter than rest of lacinia

89  Inner lacinial margin with row of at least 4-5 long seta; no prominent knob bearing pegs below subapical lacinial tooth....Isoperla  (Remember that Malirekus has that "prominent knob.")

And in Peckarsky (p.71)

41b. Lacinia without a knob, rounded or tapering from the smaller spine to base

 Beaty's description is more detailed ("The Plecoptera of North Carolina," p. 23)

Lacinia bidentate with apical tooth shorter than rest of lacinia and typically without low rounded knob; lacinial margin with row or tuft of at least 4-5 long setae, some species with row approaching base."

This description holds true for almost all of the Isoperla species I've found.  This lacinia -- along with the longitudinal abdominal bands -- will help you ID the following species: Isoperla dicala, Isoperla holochlora, Isoperla nr. holochlora (which actually lacks the longitudinal bands), Isoperla montana/kirchneri, Isoperla similis, and Isoperla davisi.  But there are some exceptions that need to noted.

1. Isoperla orata.  

The apical tooth of the lacinia is very long, as long as the rest of the lacinia.  And there is a bit of a knob below the subapical tooth on which we find exactly 3 setae.

2.  A second exception -- the nymph I've been calling Isoperla nr. orata -- in part because the laciniae are so much alike.

The lacinia differs in one important way: there appear to be 5-6 setae on the knob below the subapical tooth.

3. And for the strangest one I've seen so far, Isoperla lata.

This lacinia looks nothing like the other Isoperlas we've seen.  

Beaty's description - "lacinia distinct, broad, apex as wide as base and covered with a dense brush of setae."  Wierd, and it looks like there's only one tooth.

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I guess the point to be made is use your keys with caution: they don't always get you to the right place.  And with Isoperlas, I'd encourage you to go right to Beaty's descriptions.  Remember that his "The Plecoptera of North Carolina" is available on line.  You can download it and print it.  Go to:

http://portal.ncdenr.org/web/wq/taxonmanual.
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Isoperla nr. holochlora.  An Isoperla species on which the longitudinal stripes on the abdomen -- usually three dark bands against a lighter background -- are indistinct.

Moving into Isoperla montana/kirchneri season

As I mentioned last week, the Rapidan River is already chock-a-block full of these little nymphs.  It's the most common Perlodid stonefly we see in our streams.  From January to April they take over the leafpacks, hatching in large numbers in March and April to the delight of fly fisherman.  The Rapidan River must have spectacular hatches of "Yellow Sallies."

I've posted numerous entries (2/15/12, 2/16/12, 4/30/13, 4/7/14) discussing the problem of what these nymphs should be called.  If we lived in the midwest, we'd call them Isoperla namata.  But Isoperla namata does not occur in the east: the Ozarks and the midwest. But since our nymphs look just like namata, Beaty -- in his 2011 edition of "The Plecoptera of North Carolina" (p. 24) -- went with Isoperla nr. namata (Isoperla "nearly" namata) as the label to use.

In the northeast, these nymphs are called Isoperla montana (for "mountains") and Beaty later concluded that I. montana does indeed occur in our part of the country.  Still, there might be other species with nymphs that look much the same.  How about Isoperla montana/Isoperla sp. (i.e., either montana or a species that hasn't been named)?

Last year, Beaty informed me that we have at least two species that show up as this nymph: Isoperla montana and Isoperla kirchneri.   The adult of I. kirchneri has now been described (S. W. Szczytko and B. C. Kondratieff,  A Review of the Eastern Nearctic Isoperlinae (Plecoptera: Perlodidae) with the description of twenty-two new species, pp. 126-133): we're still waiting for the details on the nymph.

Quite a mess -- but the entomologists are making progress.  While we wait for the "nymph" section of Szczytko and Kondratieff to be published, let me review the forms of this nymph that I've found in the streams that I visit.  There are three.
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Number 1.  Unquestionably the most common form of this nymph that I see looks like the one at the top of the page: that includes every nymph that I've ever seen in the Rapidan River.   To compare this with other forms, we have to look at two critical features.  Look at the head.

On this nymph -- on all forms of this nymph --  there is a dark transverse band on the head.  Here, that band extends down to touch the lateral ocelli.

Feature two: at the very back of the head, there are two dark bars or stripes that reach from the ecdysial suture (right behind the ocelli) to the occiput (the very back of the head).
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Number two.  Now look at this nymph from South River,

and this one from Buck Mt. Creek.

We still see the dark transverse band and the bars/stripes at the back of the head.  Missing? -- the points of extension between that band and the ocelli.

Is that a significant difference?  Does it indicate a different species?  I don't know: let's hope we find out.  But I've found this form in a number of streams -- streams in which I've also found form #1 -- e.g. Buck Mt. Creek, South River, and Powell's Creek.
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Number three.  And this form is unique.  Where I have found it, it's the only form that I've found.  And, I've only seen it in Sugar Hollow's small, pristine, headwater streams, higher in elevation than the other streams that I visit.

Do you see the difference?  On these nymphs, there are no dark bars or stripes running back from the lateral ocelli to the very back of the head.  (The pattern on the pronotum also looks a bit different.)

Is that a significant difference?  Does it indicate a new species?  Again, I don't know, and again, I sure hope to find out.

But I did note one thing on interest in the Szczytko and Kondratieff study.  The adult form of Isoperla kirchneri -- as I noted -- is here described for the very first time.  The name is new, thus, no one has reported on finding this species before.  But note what they say:

"We expect it to be found throughout the Appalachians at moderate elevations in relatively pristine medium sized streams."  (pp. 132-133)

Hmm...  Could those nymphs we find in those "pristine" Sugar Hollow streams be Isoperla kirchneri?

Nothing to do by wait and see.

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Rapidan River, Part II.: Further notes on the Paraleptophlebia pronggilled mayflies

Before I start writing this entry, let me call attention to two matters of interest to at least some of our readers.

1) A major study of Isoperla Perlodid stoneflies has just been published, and it's available on line in .pdf format.  The monograph is by S. W. Szczytko and B. C. Kondratieff and is entitled A Review of the Eastern Nearctic Isoperlinae (Plecoptera: Perlodidae) with the description of twenty-two new species.  To read and/or download this monograph, go to http://www2.pms-lj.si/illiesia/html/monographs_1.html, and click on download.  This study focuses only on the adults: the nymphs will be covered in a separate issue.

2) For new or recent readers -- all of my photos are posted on Flickr.  To view, go to https://www.flickr.com/photos/aquaticinsects_of_central_virginia/sets/, and choose the album "live photos only."  I have recently added an album entitled "personal favorites" that you might also enjoy.  Full size copies of all of the photos can be downloaded at this site.  I trust you'll cite me if you use any photos.
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The leafpacks in the Rapidan River are loaded at the moment -- literally "crawling" -- with two different taxa: the Perlodid stonefly, Isoperla montana/kirchneri, and the pronggilled mayfly, Paraleptophlebia sp. (which I'm quite sure is mollis).   One of my photos from Sunday is posted at the top of the page.  And here are two more.

The gills on these nymphs, as you can see, are tracheated: the ratio is 1:3.  That's very clear in this microscope shot.

That makes it likely that these nymphs are Paraleptophlebia mollis (see Saturday's entry).   P. mollis and P. adoptiva -- on which the gill ratio is 1:1 -- appear to be, from the reading I've done, the most common Paraleptophlebias we see in the East.

When I was writing on Saturday, I assumed that the species we found was a matter of the type of stream in which we were looking.  That isn't the case.  As it turns out, each (mollis and adoptiva) has its season.   On this matter, the consensus among fly fishermen has been that P. adoptiva are in our streams first, hatching from March to May in the East: P. mollis are found later on, hatching along with P. guttata from June to August, i.e. throughout the summer.   (For confirmation, see the emergence chart in Knopp and Cormier, p. 266, and the following website, http://www.troutnut.com/hatch/47/Mayfly-Paraleptophlebia-Blue-Quills/.

However, Donald Chandler has reached a different conclusion.  In a note in Bugguide.net, Chandler states (speaking about New Hampshire): "P. mollis is a winter active species, emerging in the spring and disappearing in late June, while P. adoptiva is a summer active species first appearing here in late June."  (http://bugguide.net/node/view/176301/bgimage )Being further south in Virginia, we might expect to see P. mollis nymphs in late fall, with P. adoptiva nymphs first showing up sometime in the spring.

Obviously, this is a these that can be tested, and at the moment I think that Chandler is probably right.  It's mid-January, and at the Rapidan River I'm finding P. mollis.  As I've looked back through my photos, I find that the nymphs I've photographed in December in previous years -- in Sugar Hollow and South River in Greene County -- were P. mollis as well.

12/12/12, South River

12/13/11, Sugar Hollow

Will I continue to find only P. mollis this month and next month?  Remains to be seen.  And, will I see a changeover to P. adoptiva in the spring?  Remains to be seen.  However, one of the photos I posted on Saturday was taken on 3/3/12 at South River -- it appears to have been P. adoptiva (gill ratio of 1:1), suggesting that the change had already occurred.

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Now in all of this you will have noted that I've nicely side-stepped the issue of the "spines" on segment 9: neither mollis nor adoptiva are supposed to have them, but I can see them on both in the nymphs that I've found.   This is a place where I have to read more, but from the photos I've seen that were taken by others -- and from all that I've read -- I find it hard to believe that our Paraleptophlebias are not adoptiva and mollis.

Stay tuned!  (Oh, fly fishermen.  The Rapidan must have a HUGE hatch of Blue Quills in late winter and spring, to say nothing of the Yellow Sallies (Isopera montana/kirchneri) you're going to see!)