Sunday, March 26, 2017
Nemourid stonefly, genus Soyedina: here's where things stand
This is the stonefly nymph that I found in Sugar Hollow two weeks ago (March 9): family, Nemouridae; genus, Soyedina; species, initially undetermined. You will recall that I was intrigued by what appeared to me to be paired tubercles on the posterior edges of terga 1-7. These.
Steven Beaty was also intrigued and asked me to find more nymphs and/or adults if I could. As luck would have it, I returned to that very small stream on March 12 and found an adult. I failed in my attempts to get a live photo of that adult, but here's what it looked like when it was preserved in a vial.
I wasn't sure that this was Soyedina, but when I checked the wing veination with sources, that ID was confirmed. I sent both the nymph and the adult to Beaty. He determined, first of all, that those "tubercles" were in fact tufts of setae that look bigger than they are due to detritus. And on the adult, he feels that it's most likely S. carolinensis though the match apparently isn't exact.
Before I go any further let me add this. At the moment, only two species of Soyedina are attested in the state of Virginia -- S. carolinensis and S. vallicularia. (Stewart and Stark, Nymphs of North American Stonefly Genera, p. 217) North Carolina has a total of four: S. carolinensis, S. kondratieffi, S. washingtoni, and a new, unnamed species -- n.sp. (Beaty, "The Plecoptera of North Carolina," p. 17) The nymphs for the two species that are found in Virginia have both been described: carolinensis by Claasen in 1923 and vallicularia by Harper and Hynes in 1970.
So, is our stonefly S. carolinensis? Beaty's best guess so far, but this conclusion is not unproblematic. Why? Because Claasen's description of carolinensis makes no mention of "tufts of setae" on the tergites, surely a feature he'd note. I might add that such tufts are also unmentioned in the description of vallicularia.
We have to leave it at that though there are two other items worth noting. 1) On Bugguide.net, Tom Murray has posted a photo of a nymph that he ID's as S. washingtoni (http://bugguide.net/node/view/260938/bgpage), and, it too has those tufts of hair on the terga. And 2) there is also a photo of S. vallicularia on which those tufts of setae are present as well (http://www.shl.uiowa.edu/env/limnology/plecoptera.xml)
Lots of uncertainty here in the association of nymphs with adults. A lot more work needs to be done. Ah, but that's what Ph.D. dissertations are for!
Here's the place where I found both the nymph and the adult.