Ameletus subnotatus: the "Brown Dun" (Montana, Bitterroot River)

Two weeks ago, as I anticipated my fly fishing trip to Montana, our guide sent me the following photo of a mayfly dun that had landed on his oar.

                                     (photo by John Herzer, Blackfoot River Outfitters)

He asked if I knew what it was.  I didn't, but I dug around and found an exact match on Troutnut.com (http://www.troutnut.com/hatch/140/Mayfly-Ameletus-oregonensis-Brown-Dun): Ameletus oregonensis, the Brown Dun.

I hoped that I might find A. oregonensis nymphs when I got to Montana, so I was pretty sure what I had when I found these critters in the Blackfoot and Bitterroot Rivers.

As it turns out, I was wrong -- but let's see how I arrived at that conclusion.  I found the answer in an article by Jacek Zloty and Gordon Pritchard, "Larvae and Adults of Ameletus Mayflies (Ephemeroptera: Ameletidae): From Alberta", The Canadian Entomologist (129), pp. 251-289.  Larvae are keyed out on pp. 256-257, with important illustrations of critical features in Figures 17, 18, 20, 23 and 28.
____________________
Zloty and Pritchard, pp. 256-257

"1.  Ganglionic markings present on abdominal sternites 2-8 (Fig. 18E).....2
       Ganglionic markings absent (Occasionally visible on sternites 7-8 or on sternite 8...3"

I had no idea what "ganglionic markings" looked like until I looked at that illustration (p. 279).  It's hard to explain.  There's a dark pod-shaped dot on the anteromedial edge of the sternites, with parenthetical marks -- （ ）to each of its sides.  Here's a look at the sterna on our nymph.

No anteromedial dark spots, just a pair of light, anterolateral spots on each of the segments.   So, on to number 3.

"3. Posterior margin of abdominal sternites 6-8 with numerous spines (Fig. 28A, B) .... 4
      Posterior margin of abdominal sternites 6-8 without such spines.....6

There are spines on the posterior margins, but let me show you my photo later.

"4. Basal two-thirds or middle one-third of caudal filaments with alternating dark and light rings every two or three segments; mesal gill extension of middle gills about 50% of gill blade width (Fig. 23F); colour pattern of abdominal tergites 8 and 9 as in Figures 19C and 20B; final-instar larvae occur early in the season (April to June)....5
     Caudal filaments without alternating dark and light rings....6"

Here's a look at the caudal filaments, and yes, the middle one-third of the caudal filaments do have alternating dark and light rings,

and the colour pattern matches what we see in Figures 19C and 20B.  Terga 8 and 9 are light, as are terga 1-5: 6 and 7 are dark.

On the "mesal gill extensions of the middle gills...

I'm not sure what is intended.  Still, the gills on our nymph are an exact match for the gill pictures in Fig. 23F, so I guess we're good to go.  On to item 5.

"5.  Posterior margin of abdominal sternites 6-8 with numerous large spines at the middle (Fig.        28A)... oregonensis
     Posterior margin of abdominal sternites 6-8 without large spines at the middle but with numerous small spines laterally (Fig. 28B) ....subnotatus"

We find the latter on on our nymph.  I couldn't get a very good photo of this, but I hope you can make out the tiny lateral spines.

__________________

Ameletus subnotatus.  At 13-14 mm, it's a pretty big nymph.

This is a mayfly that is found from East to West in Canada, but in the U.S., it's only been found in CA, CO, MT, UT, and WY.   Oh, and with the similar dorsal pattern of A. subnotatus and A. oregonensis, I'm not surprised that the duns look exactly the same.
_____________

P.S.  Donald Chandler has posted a photo of Ameletus subnotatus at: http://www.discoverlife.org/mp/20p?see=I_DSC484&res=640.  On his nymph, the dark bands on the caudal filaments are basal, not in the middle

The Perlodid stonefly, Isoperla roguensis (Montana, Clark Fork River)

The Isoperlas I found last week in Montana in the Blackfoot and Clark Fork Rivers were Isoperla roguensis.  Species ID is possible using an excellent article by John Sandberg -- "The Isoperla of California (Plecoptera: Perlodidae); larval descriptions and a key to 17 western Nearctic species," Illiesia, 7(22): 202-258.  I am grateful to Steven Beaty for sending this to me.  Sandberg's very detailed description of I. roguensis can be found on pp. 244-246.  It includes color photos of the nymph and the features of the lacinia.

"Male larva.  Body length of mature larva 9-12 mm."  The nymph in my photo at the top of the page was a full 12 mm.

For description of the top of the head, let's use the following photos.

"Dorsum of head with contrasting pigment pattern and fine dark clothing setae, anterior frontoclypeus margin unpigmented...posterior ocelli with partially enclosed large light areas along outer lateral margins; interocellar area variable , from completely dark to partially light."  (This one is completely dark.)  "Occiput with irregular spinulae band extending from below eye to near median epicranial suture."  You can't see the entire band in my photo, but I've noted the direction of that band from the base of the eye to the epicranial suture.  I'll try to get a better photo tomorrow.  

"Lacinia bidentate...marginal setae initially long-stout and widely spaced, last few shorter and widely spaced, blending into and difficult to differentiate from dorsal and ventral surface setae." Sandberg's description of the lacinial features is very detailed -- I've just touched on the critical features.  (In Sandberg's photo, there seem to be 6 marginal setae.  Think that's true with this specimen as well.)

"Prontum with median light area occasionally with a thin central indistinct brown band bordered by wide dark irregular pigment bands."

For sure.

"Abdominal terga variable, usually with two distinct longitudinal dark stripes; wide light median longitudinal band sometimes bisected by faint, light brown longitudinal median band; lateral pair of dark longitudinal stripes usually not extending to lateral margins."  Good view of those stripes on this small nymph (10 mm) that I found in the Blackfoot.

_________________

Isoperla roguensis -- the "Rogue Stripetail" -- but fly fisherman go by the name of the hatch, the "Yellow Sally."  It's a big hatch in the rivers in the Missoula area, occurring in June and July.  Hope to see it some day!

A Montana Sampler: Lots of New Insects to ID

It was a very nice trip.  The fishing was great, the scenery was -- well, have a look at that photo! -- and I found a lot of new insects, all of which I have to ID.  That will take me awhile, so this is a "taste" of what's to come.

1. My favorite -- a new species of Isogenoides (Perlodid stonefly).

A real beauty.

2. A second Perlodid stonefly, a Skwala.  We saw the nymphs and the adults.   The rivers around Missoula are famous for the Skwala hatch at this time of year.  I was there to fish the "Skwala hatch".

3.  Another Perlodid, an Isoperla this time.  The "Yellow Sally" hatch can't be far away.

4. And a final Perlodid stonefly, a very young Kogotus.

5. Mayfly number 1 -- a Western Ameletus.  I'll ID this one in my next entry: it's A. oregonensis.

6. A new Cinygmula flathead.

7. A second Heptageniidae, this one a Rhithrogena.

8.  And one little caddisfly larva, one that we've seen before (see 5/1/14), Dicosmoecus gilvipes, the "October Caddis".

Fun, fun, fun.  Sure love finding new things.

Just a beautiful insect: fully mature, Perlodid stonefly, Helopicus subvarians

This morning I was off to Buck Mt. Creek where the water was still pretty high.  Still, it's the time when we find Perlodid stoneflies, and Buck Mt. Creek has proven very productive.
 

This is Helocipus subvarians, a stonefly that I first identified on 4/2/11.  It's one of the largest Perlodid stoneflies that we find in local streams: this nymph measured 22 mm.  I think I'm right in saying that I've only seen it in Buck Mt. Creek and the Doyles River.  Tolerance value is 1.2.   This nymph is very mature, in fact, I thought it might hatch in my tray while I was taking these photos.
Most striking, how dark the head is both in front of and behind the black transverse band.

On less mature nymphs, even those with dark wingpads, the front of the head is usually orange.  I.e.,

Nice find.  Such rich colors.
_________________

My other discovery today was a very small Perlodid stonefly -- ~ 5 mm -- the one we ID at the moment as a variant form of Isoperla orata.

As I've noted before, the patterns of the two (main form and variant form) are quite distinct.  On the variant form of Isoperla orata, there two dark spots behind the ecdysial suture, and the bottom of the notch at the front of the head is straight across.

But on the main form of the species, the dark spots are missing, and the bottom of the notch at the front of the head is rounded.

Also, Isoperla orata is uncommon and only found in very clean mountain streams.  I've never seen it in Buck Mt. Creek, only at the Rapidan River.  And while the variant form can be found side-by-side with the main form, it is also found in streams like Buck Mt. Creek and the upper Doyles River, good streams, but not the equal of the Rapidan River.   For more on this point, see the entry on habitat and species variation posted on 8/26/15.

___________________

Hope to get up to Entry Run in Greene County this weekend.  Next week, it's off to Montana!

Some pictures from the Rapidan River

Not much to report today.  But I was pleased with these photos, so I thought I would post them.  That's the flatheaded mayfly Epeorus pleuralis.  It's very common at this time of year in cold water streams -- like the Rapidan River.  Fly fisherman, if you're headed that way, take some Quill Gordon imitations.  These nymphs are on the bottoms of rocks, and they're numerous.  Should be hatching now anytime.

______________________

E. pleuralis on the bottoms of rocks, and Isoperla montanas crawling around in the leafpacks.  Must be March!  Isoperla montana is part of the "Isoperla kirchneri complex" -- see the entry posted last year on 9/3 --  and it's the most common Perlodid stonefly that I run into: March to mid-April.  While I've never fished the Rapidan River, there must be a prolific hatch of "Yellow Sallies" up here, and it too will be happening soon.

_________________

I was really hoping to see a mature Isogenoides hansoni nymph, as I did in March, 2011,

but no luck today.  I'll be back before the end of the month.  It's one of the rare insects that we find in this stream, and I don't want to miss it.
__________________

P.S. if you're editing photos with "Photos" on Macintosh, be sure to buy and install the extension "intensify."  I use "Photos" to crop and straighten -- that's it.  "Intensify" is the software to use.

The "rare" one: caddisfly larva, Pseudostenophylax sparsus

This is the second time I've found this species of caddisfly larva.  The first was 6 or 7 years ago at the "Patricia Byrom Nature Preserve" in the Blue Ridge in a very small, very clean stream at high elevation.  But, if you look back to the entry of 3/12/14 you'll see that my friend in Sugar Hollow, has found them in a  tiny spring seep on her land.  Right at the base of this pipe.

This "pool" is 1-2' feet square, and below this you won't see flowing water, just wet leaves and mud.  But that's where this species lives.  Steven Beaty, "The Trichoptera of North Carolina," p. 84: "Occurs in seeps and temporary streams.  A late winter-early spring species.  Rare."  It will hatch as a "Dark brown summer sedge" -- Thomas Ames, Caddisflies, p. 250-251 -- but no trout to eat them in this little pool!

There is only one species of Pseudostenophylax that lives in this part of the country -- P. sparsus.  Pseudostenophylax species are described this way by Wiggins: "...in all species mesonotal setal areas are confluent through sa1 to sa2 to sa3, and there is a transverse band of setae between the metanotal sa2 sclerites.  Sclerotized parts of the head and thorax are uniform reddish or yellowish brown, broken only by muscle scars.  Abdominal gills are single.  Length of larva up to 16mm.  Larval cases are contructed mainly of small rock fragments, the exterior uniform in outline.  Length of larval case up to 19mm."  (Glenn B. Wiggins, "Larvae of the North American Caddisfly Genera (Trichoptera, 1977, p. 278.

This larva was exactly 16mm; the case, 17-18mm.  For the continuity of the mesonotal setae, this is the best I could do yesterday.

Easy to see the transverse band between the sa2 sclerites on the metanotum.

Not much question about the color of the head.

And yes, the abdominal gills are single.

Beaty adds that the "head and thorax [are] uniformly orangish to yellowish brown with pale muscle scars."  Those pale scars show up nicely on this photo.

A "rare" one -- Pseudostenophylax sparsus.
__________________

We also looked for nymphs and larvae in the small, pristine, stream that runs through her land, emptying below into the Moormans.  The leaf packs were LOADED with Peltoperlid (Roach-like stonefly) nymphs.  Other than that, we saw a number of spiny crawlers (probably Ephemerella invaria), and some nice Perlodid stoneflies -- Malirekus hastatis and Isoperla similis.  I took a few pics of the latter.

And on the rocks, as we would expect at this time of year, lots of flatheaded mayflies, Maccaffertium merririvulanum and Epeorus pleuralis, some of the latter already mature.

Good to get out at last.  The weather's improving -- very warm, actually -- so I'm looking forward to exploring the streams.
______________

A note on the photos.  I'm not happy with the quality of the photos I'm posting.  For years, I've used the "iPhoto" software on my Macintosh to edit my photos: it's fast, efficient, and does a pretty good job.  But, Apple has replaced iPhoto with "Photos," for editing pictures.  I don't like it at all!  If you add the extension "intensify" to Photos, the results are better.  I also have "Photoshop Elements 9," which I like.  Unfortunately, "Photoshop" does not work with Apple's new system software (OS 10.11.3, El capitan), an issue that to date, neither Adobe nor Apple seems moved to address (!).  So, bear with me as I struggle to re-learn how to do this.  Maybe with practice...
___________________

And here the larva was just peeking out of its case.