Monday, January 19, 2015

Rapidan River, Part I.: A significant find -- Perlodid stonefly, Isoperla lata

I'm disappointed that my specimen isn't perfect: one of my other stoneflies tried to eat this nymph before I could come to the rescue!  Still, I knew when I was taking my photos that this was an Isoperla Perlodid I had not seen before.  It keys out to Isoperla lata.

I. lata -- nymphs ~13 mm; lacinia distinct, broad, apex as wide as base and covered with a dense brush of setae; head with wide, enclosed pale area anterior to median ocellus; ocellar triangle open behind; pronotum with dark border except extreme lateral margins; abdomen with longitudinal stripes, lateral stripes wide with median stripe narrow and interrupted.  Nymphs are relatively rare and are collected from the Mountains only from September through May.  Listed by NC Natural Heritage Program as Significantly Rare (2010).    (Beaty, "The Plecoptera of North Carolina, p. 24)

1. This nymph, still immature, was about 9 mm.

2. The lacinia is indeed very distinct -- very broad and very dense setae.  My microscope photo is a clear match to Beaty's description.

3.  For the head and pronotum, let's again use a microscope view.

While we still have this photo, let me quote from Frison as well (T. H. Frison, Studies of North American Plecoptera, Urbana, Illinois, 1942, p. 334).  "Dorsum of head with a small yellowish spot anterior to median ocellus, another yellowish spot in ocellar triangle, and with a large yellowish area on posterior part of head running forward on each side between compound eyes and lateral ocelli.  Pronotum with a broad, median, longitudinal, yellowish stripe, much narrower at anterior end than posterior end; areas each side of stripe brown to black."  All very clear in that photo.

4.  As for the abdominal longitudinal stripes -- they're a bit messed up since someone took a bite out of the body (the culprit will soon be revealed!), but the lateral stripes are wide, and the median stripe is "interrupted."

So we have a new one: Isoperla lata.  The Rapidan River is rich in Isoperla Perlodids.  This species will be added to our EPT taxa list.

I'll write up "Part II." of this entry tomorrow: I'll return to the issue of Paraleptophlebia species ID.  The river is loaded with pronggilled mayflies at this time of year.  But in this entry, let me include some additional photos from today's trip.  I found some beautiful insects -- as I always do when I go up to this river.

1. Giant stonefly, Pteronarcys biloba.  This was a bruiser -- close to 2 inches long.

2. One of my favorites, the Perlodid stonefly, Isogenoides hansoni.  "Relatively uncommon" according to Beaty and this is the only place that I've seen it.  (Ahem... they eat other stoneflies!)

3. Spiny crawler mayfly, Ephemerella subvaria.  Also rare/uncommon.  Two beauties today, a male and a female.



4. And of course, I saw lots and lots of Uenoids.  Just took a picture of one.  It was Neophylax consimilis, the only species I've seen in the Rapidan River at this location (entrance to Graves Mill path, SNP).


On to the pronggills tomorrow.  Today it was all about I. lata.

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