Sunday, January 18, 2015
Something new to explore: distinguishing the species of Paraleptophlebia (pronggilled mayflies)
My good friend in Sugar Hollow -- who is often ahead of me in doing research -- has drawn my attention to some interesting work in Knopp and Cormier (Mayflies: An Angler's study of Trout Water Ephemeroptera, pp. 268-269) on the nymphs of Paraleptophlebia (pronggilled mayflies: "Blue Quills" to fly fishermen). They note that some gills have tracheation, others do not, and there are differences from species to species in the ratio of the length of the gill filaments (remember that Paraleptophlebia gills are "forked"). Thus, in the gill pictured here
the gill has tracheation, and the ratio seems to be 1:1, while in the gill pictured here,
while it too is tracheated, has a ratio that is closer to 1:3. On the other hand, with the nymph in the photo at the top of the page, the gills lack tracheation, and the ratio is more like 1:5.
Super! We have something to go on when we look at our nymphs -- and this is Paraleptophlebia season.
Of the 11 nymphs studied by Knopp and Cormier, only four are found in Virginia: P. adoptiva, P. debilis, P. mollis, and P. guttata. As I looked at my photos this morning, I was pretty sure that I spotted 3 of these species: adoptiva, mollis, and guttata. Have a look.
P. adoptiva gills have tracheation with a ratio of 1:1. Looks good. P. mollis gills have tracheation with a ratio of 1:3, and the gills of P. guttata lack tracheation with a ratio of 1:5. Got them! I was very excited. But then I read more. There is another distinction to make: some nymphs have "spines" or "posterolateral projections" on abdominal segment 9 -- or 8 and 9 -- while others do not. On P. adoptiva, such spines are absent, but they seem to be present on the nymphs that I've found.
The same is true for P. mollis -- i.e., no spines on the abdominal segments. Unfortunately my P. mollis seems to have them on 9.
But I did have one spot of success. P. guttata does have a spine on segment 9. And while I'm not sure you can pick out in this photo
I could see it in my microscope view, so I hope you'll trust that it's there.
So where does that leave us? Using the Knopp and Cormier observations, I'd say I've found at least 3 different Paraleptophlebias, so far, in our streams. One is P. guttata. The others -- while resembling P. adoptiva and P. mollis -- appear to be unidentifed (by me) at this point. But then Beaty notes that we should leave Paraleptophlebia ID at the level of genus, with at least 8 different species confirmed in NC: adoptiva, assimilis, debilis, guttata, moerens, mollis, swannanoa, and volitans. (Beaty, "The Ephemeroptera of North Carolina, p. 40) There is, I take it, a "key" to the ID of some of these nymphs, but it's in a book that's not easy to find: J.D. Unzicker and P.H. Carlson, Aquatic Insects and Oligochaetes of North and South Carolina, 1982. A trip to the university library might be in order. In any event, we certainly have features to look for in the nymphs that we find in our various streams. Let's see what I run into tomorrow.