That's pretty cool, Don! The process of trying to sort out these little perlids has taken many turns, but the discovery of a new species is the most unexpected turn of all. :)

were from New England I might venture a guess, but from the Midwest and Southeast I will usually only venture to family, and for the West I am extremely cautious even to that point. I hadn't seen Riley's website, and in scanning over the photos it looks to be essentially for species from Utah???? One of the later photos is of a female P. decipiens, lateral view, which looks to be lighter in color. In catching a bunch of P. placida the other day I noticed that the males seemed to have slightly darker wings (photo above, and were pretty quick!), and the females a bit lighter (Bill characterizes placida as "general color yellow-brown"!!!! - it seems the descriptions aren't referring to the wings?). Perhaps this is true for decipiens also. Colors aren't used for the key to males, but for the key to females the wings of P. decipiens are "amber to dark brown," while otherwise being characterized as "general color yellow-brown" (maybe referring only to the body???) I won't venture a guess as to Cook County IL species, but certainly the color and form match that in Riley's photos.
The descriptions in this series is only treating adults, and they don't say whether if the descriptions are from fresh caught or specimens in fluid, but I have to suspect that it doesn't matter with this group (unlike chloroperlids) - I bet the colors in their descriptions are true for living adults. In any case, Rebecca Surdick covers the eastern Chloroperlidae in the same volume, and certainly the descriptions there are true to live colors. I would assume the same for the perlids.
Not sure what to say about the differences between placida and decipiens - the pronotal stripe of the color pattern certainly stands out, but pronotal color patterns are not mentioned at all in the Perlesta descriptions (the reason for not mentioning this feature is not known to me). The solid brownish pronotum of placida is a bit unusual in New England - in a quick scan of Isoperla adult descriptions I didn't notice any that have this feature. It seems to vary looking at the photos of other specimens, and I don't know what to make of that. Steve Hitchcock often treated more western species in his book on the Connecticut stoneflies, and gives some decent descriptions, but seems to have treated Perlesta as having a single variable widespread species placed as P. placida - what looks to be the very different P. decipiens is treated as a synonym!!!, so no help/hope there. Bill did treat the genus in a revision in 1989, and probably this paper would be the best resource. I have it, just need time to look it over.

If this was brought to Bill Stark's attention, or to Boris Kondratieff, I bet they would have some decisive opinions.

It is good you are digging all this problems up - it makes me look at the revisions more closely.

out I don't have the paper. Sent a note to Bill Stark to see if he has copies, and mentioned the problems with Perlesta ids.

I guess the issue is stalled for now, but I'm eager to hear Bill Stark's response. Thank you for contacting him and for your willingness to dig into all this.

I have also noticed that the males are often darker than the females. One thing I liked about the light trap photo of Nelson's decipiens specimens was that it provided a good opportunity to compare some of the variation and the differing degrees of darkening. I was particularly interested to see the variation in darkening of the ocellar triangle in the decipiens specimens. I see this in placida as well. I suppose that could just be due to the relative age of each specimen (how recently each had emerged from the nymph), but I'm not sure.

Anyway, I've enjoyed chatting with you about this, and I really appreciate your efforts. It's great that you can post so many positively identified specimens. They provide a very useful reference for comparison to some of the more questionable photos.

Stark's revision (1989). Only one species of the 20 or so Perlesta species lacks the light costal (outer/anterior) margin of the forewings, and three species are subsequently promptly booted out in the key with as having the wings dark brown to black (and dorsal body color dark brown to black). Of these, only P. cinctipes would be likely for the Cook Co IL specimen. All the following species have the wings yellow-brown to amber and dorsal body color predominately yellowish (i.e. decipiens). Pronotal color of cinctipes in adults is not mentioned, but the larva has a medial pale area (unlike placida - solid brown).
The pronotum of adult decipiens is characterized as pale brown. So, the wings of P. placida above should be amber? Maybe if I brightened the image, but this looks pretty close to me. The male tails fit, so my local problem is resolved quite nicely.
Throw in all the new species added since 1989, and it is obviously time for me to leave Perlesta behind and see if the specialists will straighten things out. I have mentioned the situation to Bill S and Boris K, will see what happens.

many thanks for the additional info, though I'm not sure if I'm more or less confused about the species IDs within Perlesta. I hope that Bill or Boris can help, because I seem to have exhausted my resources as well. Checking the distribution records for all of the states involved in the suspected Perlesta specimens didn't help at all. (Some IDs that would that seem fairly certain are not listed for their respective states, and others record too many potentially similar species for me to offer a guess.)

Would you agree, however, that all of the specimens currently in Isoperla at the genus level (here), and probably these (1,2,3) should be moved at least to the genus Perlesta? Most of the ones in the Isoperla section were initially placed there based on similarity to specimens that we have already moved to Perlesta placida.

from Boris Kondratieff. The good news is that all the Perlesta identified as such are, the bad news is that he would never, ever try to place them to species without looking at the eggs and/or male genitalia. I would think that all the other ones you think might be Perlesta are also (with the potential exception of the OK one). Further bad news is that the one above is probably not placida, which was described from the Washington, DC area originally.

I'm not surprised at Dr. Kondratieff's reluctance to commit to anything at the species level. After the problems we've already encountered with this confusing genus, I guess the best thing would be to place all but the OK specimen in Perlesta at the genus level and simply let the comments convey the possibilities and uncertainty about species.

Of course, some of this is just the nature of trying to ID based on photographs. Except for some very distinctive species, the best one can really hope to do at the species level is to say that a photo reasonably represents a species. One could always argue that some IDs can't be proven from a photo, but if they also can't be disproven, the argument becomes circular and probably moot. It's certainly not the same standard as filling out a det label. :)

Which of the OK specimens is the one you mention as a questionable candidate for Perlesta? Is it this one (1), or this one (2)?

Also, just for your continued amusement (bemusement?), I thought I'd share a couple of Whitney Cranshaw's photos of P. decipiens (1, 2). The variation of color/markings shown among these and Riley Nelson's photos is pretty striking. No wonder Dr. Kondratieff warns against trying to ID Perlesta beyond genus!

Can't remember. Both of these look like they could be. Ignore my statement of uncertainty, as this is the norm for photos of this group. I did send some properly prepared males (genitalia extruded) of our NH Perlesta off to Boris, so maybe we can end up with at least one certain identification.

I'm eager to hear what he concludes. I was just reading his 2006 paper describing the three new species described from NC and VA. This genus has grown like topsy. Back when Stanley Jewett prepared the keys for McClane's encyclopedia, there was only one Perlesta species described for North America. At that time, I suppose these would have all been considered to be P. placida. :)

for all except the Oklahoma specimen, and that one is at most a maybe. The pronotum of Oklahoma one looks strongly ridged around the margins and the costal area looks to be about the same color as the rest of the wing, so not sure. There are very few perlodids that appear as adults in summer unless possibly at higher/colder elevations/locations. I think only one summer Isoperla here (I. holoch*lora) in New Hampshire, so anything from mid-June on that looks like it could be a Perlesta probably is.