Sunday, December 17, 2017

Pronggilled mayfly, Neoleptophlebia assimilis: identity confirmed


On August the 7th this year, I suggested that most of the Pronggilled mayflies I've found were Neoleptophlebia assimilis (then called Paraleptophlebia assimilis).  That suggestion relied heavily on pigmentation.  On morphology, I was missing one piece of evidence: I needed to see the mandibles to be sure they weren't N. swannanoa.  I found a number of nymphs yesterday at the Doyles River (my upper site), and our identity can now be confirmed.

Let's work through our key (Larvae of the Souitheastern USA: Mayfly, Stonefly, and Caddisfly Species, pp. 140-141). 

263  Gills 2-7 forked at one-fourth or more length from base; gill trachea with distinctly pigmented branches at least in unforked region.........264

263' Gills 2-7 forked near base, usually not more than one-sixth length from base; gill trachea without distinctly pigmented lateral branches, but often with very short and faint lateral branches.......267

Here's our nymph.


(You'll recall that the former nymphs are now genus Neoleptophlebia; the latter remain Paraleptophlebia.)  We clearly move on to 264.

264  Mandibles relatively elongate, with about half length of angulate (left) mandible beyond angulate shelf.......Paraleptophlebia swannanoa

264' Mandibles not elongated as above, with less (usually much less) than half length of angulate mandible beyond angulate shelf........265

Here's what we have.


The portion above the angulate shelf is roughly 1/4 the length of the mandible.  We move on to 265.

265  Posterolateral projections present on abdominal segments 8 and 9.......Paraleptophlebia( i.e. Neoleptophlebia) assimilis  

[Note: projections on segment 8 are not well formed in young larvae.]

265' Posterolateral projections present on abdominal segment 9 only....266

Our larvae are very young.  Still you can see the projections on 8.


Species ID confirmed!  Neoleptophlebia assimilis.

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Lots of Large winter stoneflies (Taeniopteryx maura/burksi) around yesterday;


Small winter stoneflies (Allocapnia pygmaea) as well.


Monday, December 11, 2017

Apatania incerta -- Little Mountain Casemaker -- at the Doyles River this morning


It's a casemaker that I don't see very often -- Apatania incerta -- but it's one of the things I was hoping to see this morning.  Beaty describes the case as "composed of mineral particles and strongly curved, cornucopia-shaped."  ("The Trichoptera of North Carolina," p. 85)  Pretty clear in the photos I've taken. 



The genus ID goes like this.

Mesonotum with two plates; metanotal sa1 sclerites absent; arrangement of sa1 associated setae in a linear transverse row...mandibles usually with uniform scraper blades (not toothed).  (Beaty, p.85)  Works for me.



On the species he adds: "larvae 6-9 mm; head dark brown to black; nota brownish-black; anterior metanotal plates replaced by row of about 20 setae; legs yellow brown."  But I'm not sure the species detail is needed.  In our new key, incerta is the only species listed for Apatania.  (Larvae of the Southeastern USA: Mayfly, Stonefly, and Caddisfly Species, p. 294)

With a Tolerance Value of 0.6, we can expect to find it only in very good streams.  And when the case is right side up, the larva is covered with a hood.  Normally, all we can see is the legs, but in this case, the part of the head also sticks out.


Saturday, December 2, 2017

Our "Green Stoneflies" (Chloroperlidae), genus Sweltsa, are Sweltsa onkos


For sometime now, based on the appearance of the adults,


my friend and I have felt strongly that our Sweltsa "green stoneflies" were Sweltsa onkos in terms of the species.  With the help of our new key -- Larvae of the Southeastern USA: Mayfly, Stonefly, and Caddisfly Species -- we can now confirm that ID.   (And yes, if the genus is Sweltsa, there is nothing "green" about either the nymphs or the adults of these Chloroperlids.)

Let me work through our key (pp. 206-208). 

72  Tibial fringe setae sparse and about half as long as median outer marginal seta......73
72' Tibial fringe setae more abundant and about as long as median outer marginal seta......77


The tibal setae is dense and long.  We move to couplet 77.

77  Longest dorsal setae on last five cercal segments about as long as 1.2- 1.5 cercal segments.......Sweltsa mediana
77' Longest dorsal setae on last five cercal segments about as long as 2 cercal segments........78


I'd go with 77'.  Certainly the longest setae on at least the last three segments are close to being the length of 2 cercal segments.

78  Abdominal terga dark brown, occiput about as dark as frons; meso- and metanota rather densely covered with long dark clothing hairs.......Sweltsa onkos
78' Abdominal terga pale brown, occiput almost entirely pale; meso- and metanota with sparse, brown clothing hairs.....Sweltsa naica


That's a no-brainer: Sweltsa onkos for sure. 
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As we go through the winter, I'll keep checking Sweltsa nymphs just to be sure that onkos is the only species we have in our streams.  I can certainly say that every nymph that I have preserved keys out to onkos, and the nymphs in my photos match that description as well.







Tuesday, November 28, 2017

Exploring new waters: Rose River, Madison County


I'd like to explore some new streams in the winter and spring, so yesterday I went up to the Rose River in Madison County.  It's good water, known for some of the best trout fishing in central Virginia.  While I found a lot of good insects, I was surprised by the number of midges I found but pleased with the photos I got of them.


If you monitor streams, you come to expect these little larvae in your nets.  You might -- mistakenly, as it turns out -- assume that all midges are "tolerant" critters that indicate so-so water.  That's not true at all.   In North Carolina's list of tolerance values, there must be 500-1000 species of Chironomids listed, and they run the full range of TV's from 0.0 to 10.  So as it turns out there are "good" midges out there, and I suspect that's true of the ones I found yesterday given the quality of the water involved.  This is where I was looking.

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I didn't find anything new yesterday, but I did find of couple of nymphs that, before this, I had only found at the Rapidan River: the common stonefly, Agnetina capitata,


and the spiny crawler mayfly, Ephemerella subvaria.



I plan to back to the Rose in the winter and spring.  I expect to see some pretty good insects -- maybe even something new!
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A couple good photos of a brushlegged mayfly.  Still no way to key out the species.


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(I might add, by the way, for our readers who are fly fishermen, that almost all of the midges we see are this color.  Helps to know that for midge imitations.)




Monday, November 20, 2017

The "Strong Casemaker," Psilotreta rufa: It's a new species for me


It's not all that often that I find what I'm after, but I lucked out this morning.  This is a caddisfly that my friend found a number of years ago in the pristine stream that flows by her home, but this is the first time I've seen it.  Odontoceridae (Strong Casemaker), Psilotreta rufa.


Location?  Same stream as before.


But it didn't look like that today.  Today, the flow was reduced to a trickle.  The drought we've had here this fall has really taken a toll on these small streams in Sugar Hollow.  We were lucky to find anything in there at all.

Let's establish the species ID using Beaty ("The Trichoptera of North Carolina," p. 97)

(P. rufa) -- larvae up to 11 mm; head and pronotum uniformly reddish brown without stripes but may have darker pigmentation along frontoclypeal and coronal sutures...head longer than wide and relatively flat between carinae; seta 17 about half the length of seta 15; pronotum darker laterally; anterolateral pronotal projections short.

1) Our larva was 10 mm.

2) Yes, on the color of the head and pronotum -- "uniformly reddish brown" -- and yes, dark stripes are missing.


3) It's hard to see the frontoclypeal and coronal sutures in any of the photos I've taken.  Still, you can easily see that the entire top of the head -- the frontoclypeus -- is darker than the sides.



4) Yes, the head is longer than wide, and it's relatively flat between the carinae.  For the carinae, let me use a photo my friend took some time ago.


5) The lengths of setae 17 and 15 are critical to the ID, and I was able to get a decent microscope photo showing them both.


For sure, seta 17 is about half the length of seta 15. 

6)  I can't say that the pronotum on this larva looks darker laterally than the rest (except for tips of the projections), but the pronotal projections are definitely short.


Psilotreta rufa.

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This is the third species of Psilotreta that I've found in our streams.  On the other two, by the way, there are black stripes on the head and the pronotum.

Psilotra labida


and Psilotreta frontalis


Sunday, November 19, 2017

Looking like winter at Buck Mt. Creek


I decided to see if the small winter stoneflies have shown up at Buck Mt. Creek and no problem, there were lots of them in the leaf packs.  Above a female; below a male.


The males are smaller than the females, have smaller wingpads, and have an extension at the end of the abdomen called a "supra anal lobe".


I was a little surprised to see that the male was almost mature -- note the dark wingpads -- but it's not all that unusual.  Once they show up, they mature and hatch in a short period of time.


Two other things.  First a small common stonefly, Agnetina annulipes.



These nymphs are common in the Rivanna in the fall: Buck Mt. Creek is the only other stream in which I've found them.

And there was one, young, Helopicus subvarians Perlodid stonefly, still quite immature.


We find mature nymphs in April.

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Sunny days in the forecast.  Maybe a trip to the Rose River?

Friday, November 17, 2017

Checking the Rapidan River


Yesterday I went up to the Rapidan River to check on the flow and habitat conditions.  The good news is that the water levels are normal again: the bad news is that the leaf packs have not decomposed to the point where there are large numbers of nymphs in them chomping away.  Still, I got some pretty nice photos.

1) Above and below, the uncommon, "common stonefly" (Perlidae) Agnetina capitata.  As you can see from the posterior edge of the wingpads this one was far from mature.   For that we have to wait until June and July.



2) The "brushlegged mayfly" (Isonychia sp.).   These were quite common.




You might recall that I was hopeful that, using our new key, I could get these down to species ID.  But alas, every nymph that I've found so far has a "cluster of filaments" for forecoxal gills -- these


-- which means that I can't go any further: I'd need an electron microscope.

3) And the other thing that was common in the leafpacks was the pronggilled mayfly, Neoleptophlebia.  They were probably N. assimilis, but they're still too small for me to attempt to confirm that ID.


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Sure good to see water again in our streams.  The season's about to pick up.