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The Specimen

Isoperla (Stripetails and Yellow Stones) Stonefly AdultIsoperla (Stripetails and Yellow Stones) Stonefly Adult View 10 PicturesSeveral stoneflies of this species were flying around a small stream last night. I tied on a brown drake imitation of about the right size/color to approximate these stones, and was rewarded with a hard-fighting 17-inch brown trout.
Collected July 7, 2006 from Cayuta Creek in New York
Added to by on July 8, 2006

The Discussion

TeamrennaJune 12th, 2008, 12:19 pm
Posts: 2Edit: Post removed
GONZOJune 12th, 2008, 7:25 pm
Site Editor
"Bear Swamp," PA

Posts: 1681

Your comments confused me at first, until I realized that your perspective seems to be from a different part of the world. Neither Siphonoperla burmeisteri nor Xanthoperla apicalis is found in North America. (This specimen was collected from a small stream in New York, USA.)

...all Isoperla species are much bigger....

Perhaps that is true where you live, but some North American Isoperla are well within the size range indicated by the photo (+/-14mm from head to wingtips). As best I can sort it out, everything appears to be consistent with a perlodid ID. What structures do you see that suggest Chloroperlidae?
TeamrennaSeptember 4th, 2008, 1:00 pm
Posts: 2My bad Gonzo. I concluded to fast. Its of course a female Isoperla. I must have been blind or something when i posted my first comment.
Pay attention to the slight notch in this specimens subgenital plate (posterior, as seen in one of the pohots. What does your taxonomic keys say?
In my region (Norway),adult isoperla (grammatica, obscura and difformis) females can be separated by this feature.
This specimen has a difformis-like subgenital plate by the way.

GONZOSeptember 9th, 2008, 1:32 pm
Site Editor
"Bear Swamp," PA

Posts: 1681
My bad Gonzo.

Not a problem, Teamrenna. I always enjoy hearing from fly fishers and aquatic insect enthusiasts from other parts of the world. (And I dream of visiting your stunningly beautiful country some day!)

What does your taxonomic keys say?

I wish it were that easy. Unfortunately, if a comprehensive species-level key to all stages/sexes of North American Isoperla exists, I'm not aware of it. Many of the existing keys are either out of date or lead to a statement that says that females must be associated with males for identification. Part of the problem is that we have nearly 60 North American species assigned to this genus, and some adults are described mostly by distinctions in male genitalia. There are about 19 Isoperla species in my home state of Pennsylvania, with a few unnamed as yet.

In general appearance, this specimen looks much like Isoperla cotta. However, given the number of similar-looking species and the degree of variation among them, I still wouldn't hazard a guess about the species. Incomplete distribution records further compound our identification problems. For example, Isoperla cotta is not listed in the distribution records that I have seen for New York State, but I know that specimens identified and photographed by Dr. Whitney Cranshaw were collected there.

Lloyd (Gonzo)

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