A "rare stonefly" day at the Rapidan River: common stone, Agnetina capitata; Perlodid stone, Isoperla orata

Just a super day at the Rapidan River: I didn't know how good it had been until I downloaded my photos.  And the focus today is on stoneflies.

In the photo at the top of the page, a rarely seen common stonefly, Agnetina capitata, and we've got a mature one!   The genus ID, Agnetina, is determined by two things, and we can see both of them in this picture: 1) the occipital setal row is complete, and 2) anal gills are present.

For the species ID, let me read you Beaty's description, then we'll look at the key features in some close-ups.

A. capitata -- nymphs ?? mm; lateral arms of M-pattern on head directed laterally; dark area between lateral ocelli sometimes lighter to median ocellus; dorsum of abdomen banded, posterior margins dark and with a triangular mesal area anteriorly projecting forming an apparent mid-dorsal longitudinal stripe; apex of tergum 10 light with dark pigmentation faintly continuous mesally, sometimes with a small median projection directed distally.  Semivoltine.  Collected primarily from the Mountains.  Recorded from GSMNP [Great Smoky Mountains National Park].  Listed by NC Natural Heritage Program as Significantly Rare (2010).  ("The Plecoptera of North Carolina," p. 15)

For the record, this nymph was 14 mm.  In the following photo, we can clearly see all of the features on the head noted by Beaty.   The dark area between the lateral ocelli is indeed lighter as it extends in the direction of the median ocellus.

And for the abdominal bands and stripes and the features on tergum 10 ---

On this nymph, there is a "small median projection directed distally" as part of the dark band on tergum 10.

Perfect fit.  A. capitata is attested in the state of Virginia (Stewart and Stark, Nymphs of North American Stonefly Genera, p. 320).    I hope to find out where else it's been found and find out if it's "rare" in this state as well.

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Moving on, for the second time I found the Perlodid stonefly Isoperla orata -- I've only found it at the Rapidan River -- and at the same time found a number of Isoperla nr. oratas, one of the Isoperlas that remains undescribed and unnamed (I. nr. orata is just a "name" that I use).

Isoperla orata

Isoperla nr. orata

We can "compare and contrast" using Beaty's description of Isoperla orata.  "I. orata -- nymphs 11.5-14.5 mm; lacinia with apical tooth as long as sclerite bearing it, with a tuft of setae below the subapical tooth; head with a dark transverse band through the median ocellus and ocellar triangle enclosed with a large pale spot; dorsum of abdomen with three dark, narrow longitudinal stripes, the central stripe often faint or discontinuous. ... Uncommon."  ("The
Plecoptera," p. 24)  Have a look.

Also note how the pale areas on the terga -- especially the anterior terga -- are almost fully enclosed by dark banding, taking a circular form.  (For a more detailed look at  the features of I. orata, see the entry posted on 6/2/13.)

Isoperla nr. orata differs in two significant ways: 1) the pale spot in the ocellar triangle is not fully enclosed, appearing open at the back, and 2) the middle longitudinal stripe is as wide as the lateral stripes, not at all "faint or discontinuous."

The lacinia of the two species are almost exactly the same.  But, on I. nr. orata, there are 5-6 setae in the tuft below the subapical tooth: on I. orata the setae are 3.

I very much hope that my "I. nr. orata" is given a real name when Kondratieff publishes his study of Isoperlas.
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One other "double" showed up today: I found both Isoperla holochlora and Isoperla nr. holochlora.  The quick way to tell them apart is to look at the large pale area on top of the head.  On I. holochlora, it is fully open all the way to the labrum; on I. nr. holochlora, only the middle part of the spot reaches out to the labrum.

I. holochora

I. nr. holochlora

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Off to Europe on Thursday for a trip up the Rhine.  Back to the streams on June 11 or 12.  Gonna be hard to beat a day like today!

A. capitata

I. orata

A new species of flatheaded mayfly? Maccaffertium mediopunctatum

As I left the upper Doyles River this morning, I had this entry all figured out.  It would feature this flatheaded mayfly which I was sure was M. ithaca, and illustrate how we ID it.  Unfortunately, my stream side identification was wrong: this appears to be a species I've not seen before, Maccaffertium mediopunctatum.   Here is Beaty's description:

M. mediopunctatum -- nymphs 7-10 mm; 0-9 (usually less than 5) hairs, 4-8 (usually 5-6) spine-like setae on maxillary crown; posterolateral projections present anterior to segment 6; sternal maculations variable though usually with dark crossbands on sterna 2-8, and 9 with dark, inverted "U".  Found in the mountains only, especially rivers.  ("The Ephemeroptera of North Carolina," p. 19)

1. Our nymph measured ~8 mm.

2. While I could not get a good photo of the maxillary crown, I counted 5 spine-like setae and about 8 hairs.

3. the posterolateral projections, the dark crossbands on sterna 2-8 (can only see them on 3-8 on our nymph), and the inverted "U" on sterna 9 can all be seen in this microscope photo.

It clearly is not M. ithaca, which measures 9-14 mm with transverse sternal bands only on segments 5-6 or 7-8.

To me, the evidence for M. mediopunctatum seems very strong.  Still I'll probably check this with Beaty when he returns from vacation.  There is another possibility: M. modestum.
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The rest of the insects I picked up today were fairly predictable for this time of year.

1. Perlodid stonefly, Diploperla duplicata.

2. Perlodid stonefly, Isoperla holochlora.  Lots of them in the leaf packs.

3. And of course, I found a lot of E. dorothea spiny crawlers.

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With Patricia Byrom Park just a few miles up the road, I continued on to see what I could find in the small mountain stream that flows next to the car park.  Not a whole lot of success.

1. I saw a couple of Eccoptura xanthenses common stones, this one fairly mature.

2. The case-maker Pycnopsyche gentilis.

3. And to my surprise, there were still Uenoids on the rocks in this stream.  This one was N. mitchelli.

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Another Mac from the Doyles which I think might be a young mediopunctatum, though I need to look it over with care.

Monday, up the Rapidan River!
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Addendum:  Well, I see that on 6/14/12 I concluded that this nymph was, indeed, M. ithaca!  I plan to send it to Beaty and see what he has to say.

Drunella season: the spiny crawler Drunella cornutella at the Lynch River

I didn't know what I would find at the Lynch River this morning -- but I did not expect to see this: the spiny crawler mayfly, Drunella cornutella.  Of the three Drunella spinys that I've seen so far, this one tends to show up late in the season. D. tuberculata and D. walkeri can show up in April;  I usually see D. cornutella sometime in June.

D. cornutella has "tusks" -- well, I regard them as tusks -- "frontoclypeal projections."  And like all the Drunellas, it has very robust fore femora with sharp spines on the anterior edges.

I've already used Beaty's description to ID them (see the entry posted on 5/27/12), so I won't repeat all that he says ("The Ephemeroptera of North Carolina," p. 25).  But two key features are easy to see: "head smooth with moderately long lateral frontoclypeal projections but less than half as long as the distance between them; median ocellar tubercle blunt to moderately sharp."  You can judge the size of the projections yourselves using the photo above.  I'd call the median tubercle "blunt."

According to Knopp and Cormier (Mayflies, p. 224), Drunellas hatch as the "Eastern Blue-winged Olives."  Drunella nymphs can get pretty big so the adults must be the largest BWO's fly fishermen see during the season.  Tolerance values: D. cornutella, 0.0; D. tuberculata, 0.0; D. walkeri, 0.6.

The Drunellas:

D. tuberculata

D. walkeri

D. cornutella

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Other photos:

1. Flatheaded mayfly, genus Rhithrogena.  This is actually what I was after this morning; this is one of the few places I've seen them.  Unfortunately, I only found one, and it was still very small.
This either means the Rhithrogenas are, like so many insects this year, showing up late -- or I found a late bloomer.  As promised, I'm not going to guess at the species.

2. Perlodid stonefly, Isoperla holochlora.  It's the only stonefly species I saw.  There were quite a few of them in the leaf packs (which were few and far between).

3. And the spiny crawler that's still around in large numbers -- Ephemerella dorothea.

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Lynch River at Dyke Rd. in northern Albemarle county.  The water is still fairly high, but as you can see, our streams are dropping and clearing.

And while we're on the flatheaded mayflies...species ID is also a problem with Rhithrogena and Stenacron

We have flooding conditions in central Virginia after 5+ inches of rain dumped into rivers and streams that were already high.   Roads are closed to some of my sites, and even small streams are raging out of control.  I might get into some streams by next weekend -- but I'm concerned about what I will find.  Insect populations were surely affected by these rushing waters.  So, time for some "back burner" projects.

We've recently noted that species ID for Leucrocuta and Maccaffertium flatheads, in many cases, has not been resolved to anyone's satisfaction.  The same is true for Rhithrogena and Stenacron nymphs.  Beaty recently told me (e-mail) that species ID for family Heptageniidae nymphs (the flatheads) still requires a whole lot of work.  So an "update" might be in order for the Rhithrogena and Stenacron nymphs that we've found, so far, in our streams.
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I.  genus Rhithrogena

Rhithrogena flatheaded mayflies have gills that resemble those of Epeorus flatheaded mayflies: they are discs surrounding the tergites spreading out like a fan, acting like suction cups to help these "clingers" hold onto the rocks in fast-flowing water.  However, Rhithrogenas have three tails, not two, and on the underside of the nymph, the gills touch at the top of the bottom forming an oval (Epeorus gills do not meet at the back end).

In the first EPT list for central Virginia that I posted, the Rhithrogena in the photo at the top of the page was identified as R. jejuna.  That ID was based on the fact that it matched the photo of R. jejuna posted by Donald Chandler (see: http://www.discoverlife.org/mp/20q?search=Rhithrogena+jejuna).   But Beaty does not list R. jejuna as a species found in NC ("The Ephemeroptera of North Carolina," p. 22), and in other sources I've now discovered that R. jejuna is only found in the northern tier of the country.  When Beaty looked at my photo he said that it might be R. exilis which he describes in the following way: "terga 1 and 2 pale yellow, 3-6 reddish brown, 7 pale; middle portion of head yellow or light brown contrasting with darker lateral areas." (p. 22)  This is a pretty good match.  The middle of the head certainly contrasts with the sides, and terga 1 and 2 are pale yellow (look between the wing pads).  But on my nymph, tergite 7 is not at all pale while terga 8 and 9 certainly are.

So, the species ID is uncertain.  Beaty himself says that he's not at all comfortable taking the Rhithrogenas to the level of species: more work needs to be done.

Some of the other Rhithrogenas I've found...

1. could be R. uhari: "abdominal tergites light chestnut or cinnamon brown with no pattern." ???

2. could be R. amica: "mostly all brown but there may possibly be two distinct color patterns." ???  The description doesn't really narrow it down.

and there are others.

In Beaty's descriptions, the colors are very important.  But I can't be certain of any species ID with the insufficient data that he can provide at this point of the game.

I've found Rhithrogenas in the Lynch River and Buck Mt. Creek in March, April and May.  Not sure I'll get a chance to see any this year.  If I do, I'll probably leave them at the level of genus.
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II. genus Stenacron

Where do we stand with the Stenacron nymphs in our streams?   Beaty describes three different Stenacron species: carolina, interpunctatum, and pallidum.  ("Ephemeroptera," pp. 22-23)  I think we've seen all three in our streams, but I need to find more specimens to be sure.

1. Stenacron interpunctatum.

I feel pretty good about this ID.  "nymphs 8-11 mm: 7-10 spines on maxillary crown; white streaks, often in H-pattern on tergites 8-9; caudal filaments with alternating banding pattern. A spring and summer species.  The most common and tolerant Stenacron species in NC." (Beaty, p. 22)  There are obviously white streaks on the abdominal terga, and we can also see the banding on the tails.

I found this nymph in June, 2011 in the Mechunk.  That's so-so water, so this is clearly a tolerant species.

2. Stenacron pallidum

This is a "maybe."

"S. pallidum -- nymphs 6-8 mm; pale triangular spot anterior to median ocellus approximately as long as wide (provisional); 11-13 spines on maxillary crown; usually all grey-brown, but can have pale streaks or "H" but thinner and less conspicuous than in S. interpunctatum." (pp. 22-23)

The color is right; so too is the size of the pale triangle in front of the median ocellus.

But this nymph is immature.  I need to find a mature one and look at the spines on the maxillary crown to be certain of my ID.

3. Stenacron carolina

This too is a "maybe."

My friend in Sugar Hollow found this one in April in the small headwater stream that flows by her house.  The photo is hers.

Beaty: "S. carolina -- nymphs 10-13 mm; length of pale triangular spot anterior to median ocellus approximately 2X it's basal width (provisional); 7-10 spines on maxillary crown; dorsum of abdomen grey-brown without conspicuous markings; caudal filaments all light grey-brown with no banding.  Usually in small mountain streams.  Collected spring to summer.  Uncommon."

The color is right.  So too is the size of the pale triangle in front of the median ocellus.

From what we can see of the tails (caudal filaments), I'd say they're unbanded.  And she's found a number of things in her "small mountain stream" that were "uncommon."   Still, we need to preserve one of these nymphs to see the spines on that crown.
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This is the time to look for these flatheaded mayflies.  But the weather just isn't our friend.