Thursday, May 21, 2015

A "variant form" of Isoperla orata

Nymph #1, Isoperla orata

Nymph #2, Isoperla orata, variant form

When he first saw nymph #2 two years ago, Beaty felt that it wasn't the same as nymph #1.  After close study, at the moment he feels that they might be the same -- Isoperla orata -- with nymph 2 being a variant form.  Nymph #1 was tagged as Isoperla orata some time ago (T. H. Frison, Studies of North American Plecoptera, 1942, --. 323-325).  Given the different patterns we see on nymph #2 (both head and abdominal patterns, see the entry of 5/15), it would have to be a variant form.

Beaty admits that we can't be sure of the ID of nymph #2 until someone rears it and we see the adult. In the meantime,  I'll simply call it "Isoperla orata vf."  (vf for variant form).

I have nagging doubts.  Isoperla orata vf. is a stonefly that I've found in three, quite different streams: the Upper Doyles River, Buck Mt. Creek, and the Rapidan River.  The Rapidan River is the only place I've seen I. orata.  And, when I was up there last week, I. orata vf. nymphs were a dime a dozen, I only saw one I. orata.   In fact, in four years of looking, I've only found four I. oratas.  There are differences that must be explained.

Upper Doyles River (in winter)

Buck Mt. Creek

Rapidan River

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