I found this green stonefly (family: Chloroperlidae) on 5/17 in a very small -- but beautiful -- stream in Sugar Hollow, and on 5/18 I made a tentative call of genus Alloperla. This is an uncommon genus, one I've not seen before. But then two days ago I found a another one in the Doyles River. This one.
I now think it's possible that the immature Chloroperlid (pictured below) that I found at Buck Mt. Creek on 5/11 was an Alloperla as well, so I'm hopeful that I'll run into more of these in the near future.
In this entry, I'd like to make the best case I can for the identification of Alloperla using a detailed description, illustrated with some microscope photos I've taken. The description I'll use comes from the chapter on Chloroperlids -- "Chloroperlidae (The Sallflies)" -- by Rebecca F. Surdick, which is pp. 1-60 in Bill P. Stark and Brian J. Armitage (Editors), Stoneflies (Plecoptera of Eastern North America, Volume II: Chloroperlidae, Perlidae, and Perlodidae (Perlodinae) (Columbus, Ohio: Ohio Biological Survey, Inc., 2004). Surdick's words are in BOLD type. (See pp. 5-6 in her chapter).
(p. 5) Nymph. Habitus [body shape] more streamlined, elongate than other Chloroperlinae.
No doubt about it. It's the first thing I noticed when I found these nymphs. Two additional photos for making this point.
Compare this to the Chloroperlid that we saw all winter long, which was genus Sweltsa: note especially the different shape of the abdomen.
Surdick continues: Laciniae usually terminating in single tooth and comb of two to ten regularly spaced even-length spines (bristles.)
The single tooth and the comb of spines are clearly visible in this microscope photo.
Pronotum with fringe of single or clustered long setae, usually restricted to corners.
This is the best photo that I could get of the pronotum. Note that there are no setae on the anterior and posterior margins of the pronotum -- they're only at the corners. (The number and length of these "corner" setae, by the way, is important in determing species ID.)
Again, let's compare this to the pronotum of a Sweltsa nymph, which does have setae on the anterior and posterior margins (we'll just look at the posterior edge).
Wingpads nearly parallel to oblique on interior margins.
The "creamy" wingpads themselves appear to be parallel, but the inner margins -- edged in gold -- are clearly oblique. (And look at the wingpads on the nymph pictured at the top of the page.)
This is the best photo I could get of the tergites, and the body setae are so pale you can hardly even see them. If you click on the photo to enlarge it, you might be able to see some of the setae on the posterior margins of some of the tergites: I can't see any setae in the middle (medially).
Compare this with the relatively "hairy" body of a Sweltsa nymph, on which the setae on the posterior margins of the tergites is very easy to see. (Click on the photo to enlarge it.)
Even hairier, the wingpads and abdominal segments of this very young Sweltsa nymph.
Cerci usually plumate; each segment on distal two-thirds with one to a few dorsal and ventral long setae extending posteriorly from posterior margin and as long as to longer than segment, usually with delicate intercalary hairs in dorsal and ventral longitudinal row.
This is a difficult photo to get. To see the "plumate" character of the ends of the tails -- produced by the presence of intercalary (i.e. inter-segmental) hairs, you must have a lateral view of the tails, i.e. you have to turn the nymph on its side. The photo that follows is not very good, but it's the best I could get.
The cerci in the photo above are those of the nymph that I found on Thursday. As I noted before, I was not able to see these intercalary hairs on the nymph that I found on 5/17. What are clear on the 5/17 nymph, however, are the "few dorsal and ventral long setae," that extend "posteriorly from the posterior margin and [are] as long as to longer than [the] segment."
Why the tails on some of our nymphs do appear to be plumate while those on others do not is something I'm working on with a friend. However, both Surdick and Stewart and Stark (Nymphs of North American Stonefly Genera, p. 253), say that this fringe is usually present. Perhaps this varies with species.
I will not attempt to identify our Alloperlas to the level of species. Beaty notes that of the seven species of Alloperla in North Carolina "most of these species are undescribed." (Beaty, "The Plecoptera of North Carolina," p.9). Obviously, a lot of work remains to be done by entomologists on this genus of Chloroperlid. In Virginia, by the way, according to Stewart and Stark (p. 256) there are at least ten species of Alloperla: A. atlantica, A. banksi, A. biserrata, A. caudata, A. chloris, A. idei, A. imbecilla, A. nanina, A. neglecta, and A. usa. A. petasata should probably be added to make it eleven. Descriptions and illustrations of A. caudata, A. chloris, A. idei, A petasata, A. usa, A. voinae, and A. vostoki can be found in Bill P. Stark & Boris C. Kondratieff's article, "Larvae of Eight Eastern Nearctic Allopera Species (Plecoptera: Chloroperlidae)," which is available online at: http://www2.pms-lj.si/illiesia/papers/Illiesia06-20.pdf.