The nymphs I've been calling Isoperla similis must now be designated "Isoperla similis/pseudosimilis Groups." Let me cite Beaty's words: "similis/pseudosimilis Groups -- (photographic guide: pages 33-34) -- nymphs of these two groups are currently inseparable without associated reared material. Isoperla cherokee has been reared from various localities and provided the most nymphal specimens for study. All specimens that match the description of Isoperla cherokee should be identifed as "Isoperla similis/pseudosimilis Groups". " ("The Plecoptera of North Carolina," version 4.0, p. 65)
As noted yesterday, these "groups" are comprised of 7 different species: I. bellona, I. cherokee, I. starki (I. similis Group), I. pauli, I. pseudosimilis, I. reesi, and I. stewarti (I. pseudosimilis Group). Curiously, I. similis -- I assume there still is such a species -- is not included, and Beaty notes: "no verified material of Isoperla similis, long thought to occur in NC, has been found in NC." ("A morass of Isoperla nymphs (Plecoptera: Perlodidae) in North Carolina: a photographic guide to the their identification," 2015, p. 33) In personal communication, Beaty tells me that all of the nymphs from VA that he has reared so far were Isoperla pseudosimilis.
Other bits and pieces of interest (photographic guide, p. 33) --
- species in these groups appear to be restricted to small, cold, high elevation streams
- preliminary morphological differences between at least some species are unproven but promising
- can possibly be confused with the perlodid Malirekus hastatus (size and lacinia will separate)
- tolerance value(s) = 0.80 (even as a group, this habitus pattern is only found in high quality waters)
- reared and positively associated: I. cherokee, I. pauli, I. pseudosimilis, I. reesi (B.K.), I stewarti (B.K.) (note: B.K. stands for Boris Kondratieff)
Obviously, we can't do much more with the nymphs that we find until clear morphological distinctions by species have been determined.
To date, I've found nymphs of this sort in Entry Run (photo at the top of the page)
Sugar Hollow --
and the Rapidan River (for example, the nymph I found yesterday). I've found them from February to April.
And while I'm on Isoperlas, I should note that another new species has been found in VA: Isoperla evanescens. Detailed descriptions of this species -- both the adult and the nymph -- can be found in the recent article by Chris J. Verdone and Boris Kondratieff, "A new species of Isoperla Banks (Plecoptera: Perlodidae) from the Appalachian Mountains, Virginia & West Virginia, U.S.A., Illesia, 12 (13), pp. 74-85.
With any luck, we'll be able to nail down the ID of the nymph that we find in Sugar Hollow -- Isoperla sp. VA (pictured below) -- later this year. Beaty plans to come up in May to take some nymphs back to NC to rear.