Wednesday, May 4, 2016

The "tiny" Green stonefly (Chloroperlidae), Haploperla brevis

The rain doesn't want to let up.  We've had over 3 inches in the last few days with more on the way.  So, we're very restricted at the moment in terms of the streams that we can explore.  It's a bummer, since this is THE time of year to find so many good insects.  Moreover, the cloudy, drizzly weather makes photography very difficult.  The photos today are not very good: I cranked the ISO up to 400 and used the flash, but that sacrifices detail.  We take what we can get.

I decided to look at the Whippoorwill Branch of the Mechums.  It's very small and tends to stay clear even in rainy weather.  And I was very pleased to find this little stonefly: this is only the third one that I've seen.  It's the Green stonefly, Haploperla brevis.  (I've found it in this stream before.)

Beaty notes the "key" features as follows: "Genus Diagnosis: Nymphs - 7 mm...pronotum with sparse setae, longest and most numerous at anterior corners; long pronotal fringe hairs are at least 0.3-0.4 times the pronotal width; inner margin of hind wing pads subparallel to body axis; pronotum and tergites lightly setose...body light brown, nearly concolorous." "H. brevis -- fits genus description." ("The Plecoptera of North Carolina," p. 9)  He adds, "Primarily found in gravel and riffle ares of small to medium streams."  That's where I was looking.  Tolerance value for this one is 1.4.

The nymph that I found this morning was very small, only 6 mm, but it's easy to see that, yes, the color is light brown, the entire nymph being much the same color.  For more detail on diagnosis, we need microscope photos.

As you can see, the hind wingpads are subparallel, and in this shot you can see at least 1 seta on the pronotum with many more at the posterior corners.

For the long setae at the corners of the pronotum, we have two photos.  You can judge for yourselves on the length of the longest of setae.  I have no problem calling them 0.3 - 0.4 times the width of the pronotum.

I've wondered this morning about the species ID.  Beaty describes another species -- fleeki -- that is tempting as well.  "pronotum with antero- and posterolateral margins dark, contrasting with light brown almost diamond shaped interior; abdominal tergites with transverse banding along posterior margins slightly widening laterally."  With our nymph, the prontoum has a dark margin, but it's around the entire pronotum save for medial interruptions on the front and back edges.

Moreover, there does not appear to be banding on the terga.   One other thing, apparently H. fleeki has only been found in the "Sand Hills" of North Carolina: brevis is collected "from [the] Mountains and Piedmont.  Think we've got H. brevis.

I saw a variety of insects today -- spiny crawlers, some rolled winged stoneflies, and lots of fingernet caddisfly larvae.  And there were quite a few small minnow mayflies, which turned out to be Baetis pluto.

There are two features that give this one away.  1) On B. pluto nymphs, there is a pale area/line parallel to the eye, and 2) "tergum 5 [is] relatively pale, [while] segments 6 and 7 [are] almost completely dark."  (Beaty, "The Ephemeroptera of North Carolina," p. 6)


May the sun come out soon and the streams drop and clear.


Note:  According to Nature Serve Explorer, H. fleeki has only been found in North Carolina.

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