Monday, November 12, 2012
As we enter "Large Winter" season -- can we distinguish Taeniopteryx burksi from Taeniopteryx maura?
Apparently not. Shoot! I thought this ID was a lock. And if you've read my entry for 10/28 you know why. The Taeniopteryx large winter stoneflies I find in our streams -- like the one in the photo above -- are an exact match for Taeniopteryx burksi as that species is described by Steven Beaty ("The Plecoptera of North Carolina," p.8). T. burksi is the first Taeniopteryx species that Beaty describes, so the ID being certain, I failed to read his descriptions of other species. But a good friend of mine did, and on Saturday she texted me to ask how I knew these large winters were not T. maura? Had I seen what Beaty had said on that species?
This is what Beaty says: "(T. maura) -- Male nymphs ~8.7-9.5 mm, female nymphs ~10/12 mm." Those are the same sizes he gives for T. burksi. He continues, "pale abdominal stripe similar to T. burksi; inner margin of hind femur with developing femoral spur of adult." But there's more. In his "Notes," he adds: "...it may be very difficult to separate T. burksi and T. maura nymphs without associated adults. Therefore, it is best to leave Taeniopteryx at genus."
I've examined the nymphs in my collection, and I did not see any "femoral spurs" on the hind femurs.
Still, I decided I had better read more. So I looked at the T. maura description in Peter W. Claassen's Plecoptera Nymphs of North America (pp. 194-195). He says a number of things of importance. 1) "General color yellowish with brown markings." I'm not sure I'd describe our nymphs in that way -- but let's move on. 2) "Head a little narrower than pronotum; entire occiput covered with mottled brown marks; there is also a brown spot each side of the ocellar triangle at the base of the antennae and another in front of the anterior ocellus." Let's have a look:
The occiput (back of the head) is certainly covered with mottled brown marks: I'm not sure about the brown spots at the front of the head, I could go either way on that one. 3) "Pronotum a little wider than long, slightly widened posteriorly; angles rather broadly rounded; a broad, median, yellow stripe, on each side of which the rugose discs are of a darker brown color." But while he notes the yellow stripe on the pronotum, he describes the meso and meta-notums as "brownish," and the abdomen as "more or less uniformly brownish."
T. maura, as Claassen describes it, seemed to me to differ from the nymphs that we find, so I still felt good about the T. burksi ID. But I thought, for good measure, that I'd best look at Stewart and Stark's Nymphs of North American Stonefly Genera, to see what they had to say about the Taeniopteryx species that occur in our state. They discuss Taeniopteryx on pp. 242-246, and on 246, we learn that T. burksi and T. maura are both found in Virginia. But the illustration of a Taeniopteryx nymph that they provide is an illustration of T. maura (p. 243), and it's a dead ringer for the nymphs that you see in my photos: the yellow stripe runs the full length of the body.
Deflated, I turned to my last resort. I sent some photos to Steven Beaty and asked if any recent work had been done that would help us to distinguish T. burksi and T. maura nymphs. As he has done so many times in the past, he kindly responded to this amateur's question, making the same point that he made in his Plecoptera document: you cannot tell them apart unless you have an associated adult. That means, if we want to be sure if the Taeniopteryx nymphs that we find in our streams are T. burksi, we have to collect some adults this winter (January and February) in the same places we've been finding our nymphs and ID the adults.
I don't know if I can do that. But, we do have a key that describes the adults for both of these species:
Bill P. Stark and Brian J. Armitage (Editors), Stoneflies (Plecoptera of Eastern North America, Volume I: Pteronarcyidae, Peltoperlidae, and Taeniopterygidae (Columbus, OH: Ohio Biological Survey, 2000), pp. 63 and 65.
I'll let you know if I'm successful. Until then, I'll refer to our nymphs as Taeniopteryx burksi/maura -- just to be on the safe side.