Monday, September 7, 2015

The beginning of fall at the Rapidan River

It still doesn't feel a whole like fall in Virginia, but the leaves are coming down in the mountains.  Lots of insects moving around in the leaf packs -- both stoneflies and flatheaded mayflies.

In the photo above, one of the stoneflies I'm always happy to see -- I've only seen it four times -- the Perlid (common stonefly), Agnetina capitata.  It's too uncommon to be assigned a tolerance value in North Carolina.  In fact, in 2010 it was listed as "significantly rare" by the NC Natural Heritage Program.  (Beaty, "The Plecoptera of North Carolina," p. 15)  But the Rapidan River is a high quality stream.

A. capitata -- 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.  (Beaty, p. 15)  And remember, Agnetina nymphs have anal gills, and they have a thin setal row at the back of the head.

It's a young one.  We find mature nymphs in the spring.  Got a very cool photo when that nymph turned on its side.


There are still some Epeorus vitreus flatheaded mayflies around and also some mature, Maccaffertium ithacas.  I got a nice picture of one that was fully intact.

It kindly turned over so we could see the transverse bands on the sterna with the characteristic "anterolateral projections."


Also present in significant numbers, the "fall" caddisfly case-makers: the "humpless case-maker," Brachycentrus appalachia

and the "strong case-maker," Psilotreta labida.


Thursday, September 3, 2015

Updating the Isoperlas: a study forthcoming from Steven Beaty

There is exciting news for those of us intent on identifying the Isoperla Perlodids we find in our streams.   Steven Beaty will soon put online a summary of the work he has done on Isoperlas, detailed notes on where things stand at the moment.  The title -- "A morass of Isoperla nymphs (Plecoptera: Perlodidae) in North Carolina: a photographic guide to their identification," (Department of Environment and Natural Resources, Division of Water Resources, Biological Assessment Branch, Raleigh).  It features photos of preserved nymphs, and photos on which are noted key features used in species ID.  I'll let you know when this comes out and where it can be found.  But since he has shared with me a copy of this in advance, I thought I might sum up the data that is important to us.

1. Photos and descriptions of the following nymphs are included.

Isoperal burksi
Isoperla davisi
Isoperla dicala
Isoperla cf. fauschi
Isoperla frisoni
Isoperla holochlora -- light form
Isoperla holochlora -- dark form
Isoperla kirchneri complex: I. kirchneri, I. montana, I. siouan, and I. tutelo
Isoperla lata/pseudolata
Isoperla orata
Isoperla poffi
Isoperla powhatan
Isoperla similis/pseudosimilis Groups: I. bellona, I. cherokee, I. pauli, I. pseudosimilis, I. reesi, I. starki, I. stewarti
Isoperla slossonae
Isoperla "Collins Cr" n.sp.
Isoperla "Mayo R" n.sp.
Isoperla nr. holochlora
Isoperla nr. transmarina
Isoperla sp. 10

Appended to the work at the end, photos and a description of Isoperla sp. VA.

2. Of special interest, the nymphs we've been calling Isoperla montana, Isoperla montana/kirchneri, and Isoperla montana group -- these (and the one at the top of the page)

are now labeled "Isoperla kirchneri complex."  This complex includes four different species -- kirchneri, montana, siouan, and tutelo -- but distinct species descriptions have not yet been made.  (Beaty notes, however, that "preliminary morphological differences between species are unproven but promising," p. 23.)  Nymphs of this complex are described in the following way: "head with irregular transverse M-type medial band, extensions back towards posterior ocelli variable, anterior frontoclypeus with 2 pair of small brown markings, some specimens with markings narrowly connected by brown lines or even widely coalesced into a larger brown area." (p. 23)

To wit...


3. Also relevant to recent entries I've posted -- the I. holochloras have been renamed: "Isoperla holochlora -- light form", and "Isoperla holochlora -- dark form".

light form

dark form

Beaty confirms what I have found -- that the "light form" is fairly widespread and found in the mountains and piedmont while the "dark form" is confined to the mountains.  He also notes, on the dark form, that the dark form "co-occurs with light form of holochlora but emerges 1-2 months earlier and when both forms are collected together, the dark form specimens will be much larger."  (p. 21)  That sums it up.

Related to I. holochlora is I. powhatan ("part of the holochora complex," p. 31).  The front of the head looks much the same.  However, the abdomen of powhatan is fairly dark, and the "ocellar spot" resembles an inverted U.  I can't say for sure that I've seen this, but I am intrigued by this photo I took on 5/31/11.

On "light form" nymphs, that ocellar spot is normally "sub-triangular to diamond-shaped" (p. 19).  I.e. like this


4. One more -- Isoperla similis.  We are now presented with two different groups: Isoperla similis Group, and Isoperla pseudosimilis Group.  In the former, we have three species -- I. bellona, I. cherokee, and I. starki; in the latter, four species -- I. pauli, I. pseudosimilis, I. reesi, and I. stewarti.   But no way is provided to tell them apart at the level of nymphs.  (Again, "preliminary morphological differences between at least some species are unproven but promising."  (p. 33)  Still, Beaty does confirm that "species in these groups appear to be restricted to small, cold, high elevation streams."  That's where we find them.

small headwater stream in Sugar Hollow in April

Entry Run in Greene County


5. So what are the species that we've found, to date, in our streams (Albemarle, Greene, and Madison Counties)?  Well certainly four of those listed by Beaty: I. kirchneri complex, I. holochlora -- light form, I. holochlora -- dark form, and I. similis.  Possibly I. powhatan, but I'm far from sure about that.  What else?  There are five more we can note.

1) Isoperla davisi

Beaty: "widespread but more common in Piedmont and Inner Coastal Plain." (p. 12)  Both of these nymphs were found in Buck Mt. Creek, the only place that I've found this species so far.  I think -- but don't know for sure -- that the spread wingpads on the second nymph are a sign that the nymph is getting ready to hatch.

2) Isoperla dicala

Beaty: "occur in small, cold, higher elevation streams of good or excellent water quality; uncommonly collected." (p. 13)  I've found them in Buck Mt. Creek and the Rapidan River.

3) Isoperla lata/pseudolata

Beaty: "found in high, cold, excellent waters (so far). ... relatively rare. ... may be pattern differences between lata/pseudolata but are, as of yet, unproven." (p. 25)  I've only seen one -- at the Rapidan River.

4) Isoperla orata

Beaty: "High quality, small to medium mid-elevation, cold water streams." (p. 27)  The first two nymphs in the photos above were found in the Rapidan River, the third was in Buck Mt. Creek.  I still think that nymph number one differs from nymphs two and three -- see the posts of 5/15, 5/21, and 8/26 -- but no distinction is made in this study.

5) Isoperla sp. VA

While this species has not yet been found in North Carolina, as Beaty says, it is "likely to occur." (p. 48)  He notes, "nymphs so far collected from small headwater streams from VA; along Blue Ridge Parkway (Bedford and Botetourt Co., D. Lenat), White Rocks campground on WV/VA border (Buchanon Co., V. Holland), and in central VA from the northern Piedmont (Albemarle Co., R. Henricks)."

In closing, I should note that Beaty adds a "Disclaimer" at the very beginning: "This manual is unpublished material.  The information contained herein is provisional and is intended only to provide a starting point for the identification of Isoperla within North Carolina.  While many of the species treated here can be found in other eastern and southeastern states, caution is advised when attempting to identify Isoperla outside of the study area.  Revised and corrected versions are likely to follow."

But it is a place to begin and gives us -- as amateurs -- a great source to use as we continue to search for these beautiful stoneflies.  Anxious for the new year to begin!  Three species -- frisoni, slossonae, and nr. holochlora -- should occur in the types of streams that I visit ("high quality, cold water streams").  I'll be looking.

Saturday, August 29, 2015

Speaking of variation...the small minnow mayfly, Acentrella nadineae

It's one of my favorite small minnow mayflies.  We see it in the summer, and I hope to see some tomorrow at the Lynch River.  Acentrella nadineae.  The orange/red markings are very distinctive, as are the gills with that pigmentation.  "Gills elongate, asymmetrical, and with basomedial pigmentation splotches; distinct abdominal color pattern often tinged with red."  (Beaty, "The Ephemeroptera of North Carolina," p. 4)

And it's a nymph that I've seen in all shapes and sizes, from very small,

to fully mature.

Even one that hatched out in my bowl.


 and after

Most of the nymphs that I've found have looked much the same: dark brown body with spots of orange on the terga, the "shoulders," and even the "neck."  Here are some photos.

But on occasion I find variation, and these two really stick out.

1) Number one is a nymph that I found -- well, I found several that day -- in the Lynch River on 7/2/11.

From the gills and the orange areas on the terga, we can clearly see that it's nadineae, but it's unusually green.

2) The other "odd man out" is this nymph that I found at the Doyles River on 7/26/12.  And again, I had others like it that day.

What is striking with this one is the pale strip that goes up through the center.  The center of every tergite is pale, but orange posteromedially.

If you look at the other nymphs in our photos, that pattern is not characteristic.  This is more common.

Terga 1, 5, 8, 9, and 10 are pale with the orange, but 2-3 and 6-7 are dark.

Now, this could be a matter of development and maturation -- gills tend to darken on nymphs as they mature.  Still, if you look at the "tiny" insects in the photos above, you can see that even there, terga 2-3 and 6-7 are much darker than all of the rest.

Habitat?  Water chemistry?  Types of nutrients in the water?  Maybe someday we'll know what explains these variations.

Wednesday, August 26, 2015

The question of habitat and species variation

I've been saving this one for a rainy day.  It hasn't been raining -- but there's not a lot more to do at the moment.

I've written a number of entries this year on a number of species where we're finding variant patterns.
True of Isoperla orata (5/21), Isoperla holochlora (5/16) and Isoperla montana (1/25 and 4/17).  Here's a reminder of the patterns we've found and where we have found them.

1. The "standard" pattern for I. orata -- the one that matches the species descriptions we find in the keys -- is this one:

This is a nymph that I have only seen at the Rapidan River.  But there is a variant form.  This.

It differs from the standard nymph in the following ways.

This is a pattern I also see at the Rapidan River, but I see it elsewhere as well: the upper Doyles River and Buck Mt. Creek, streams in which I do not find the "standard" form of the nymph.

2. Isoperla holochlora.  The normal form of this insect can be found in a lot of our streams.  Buck Mt. Creek, Powell's Creek, the small, first order streams in Sugar Hollow, South River and the Rapidan River.  It looks like this.

But there is a variant form that I've only seen in two of our streams: the Rapidan River and its tributary Staunton Run.  It's a larger nymph, with a different pattern on the front of the head, and one on which the abdominal stripes are hard to distinguish.

Nonetheless, according to Beaty, it hatches out as the same adult of the normal form of the insect.

3. And then there's Isoperla montana for which we find a number of patterns.  But this is the most common pattern I see.

Again, this pattern in "common."  A lot of our streams are simply loaded with these nymphs in the spring (go in March and April).  The Doyles River, Buck Mt. Creek, Powell's Creek, the Rapidan River, South River and so on.  But there is a variant form that I only see in the small streams in Sugar Hollow, and in those streams it's the only form there.

Note the absence of the dark bars behind the lateral ocelli at the back of the head.


What's going on?  Why do certain patterns occur in one stream but not another, variations of the very same species?    It could certainly have something to do with stream location and size.  The Rapidan River is a mountain stream, but it's a fair sized mountain stream as it comes out of the Shenandoah National Park.

Buck Mt. Creek is a mid-sized stream in the rolling hills east of the Blue Ridge which is 8+ miles away.  Where I go to look for insects, it has already passed through some farms.

The upper Doyles River is also at the base of the mountains, but it does not have the size of the Rapidan, nor is the vegetation as dense.

And the head water streams in Sugar Hollow are also in the mountains, but they're very small.

As entomologists start to work on these species variations surely the location and size of the stream will be a relevant factor, but there may be other factors as well.

In discussing variations in A. evoluta, Steven Beaty had this to say on variation in pattern.  (These are simply musings by Beaty, and should not be quoted as some kind of final position.)  "Patterns can be influenced by maturity level, temperature, habitat, region, preservation method, UV light, diet, and who knows what else (pollution?). "  Sure will be fun to see what they find.