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Kogotus vs. Rickera
For California aquatic bioassessment, we routinely leave perlodid nymphs with unidentate lacinia at the provisional (colloquially, "slash ID") taxon “Kogotus/Rickera”. The reason for this is that the single character given in the various keys (Stewart and Stark, 2002, for one) is the presence of a transverse suture connecting the anterior corners of the furcal pits for Rickera. This character is considered absent for Kogotus. However, this is not a straightforward character. According to my colleague and Plecoptera specialist, John Sandberg, this is actually a character of the adult showing through the larval exoskeleton. We’ve seen the cuticle fold in that exact location on Kogotus nymphs from Colorado, thus making them appear to be Rickera, even though we’ve had associated Kogotus modestus adults from those locations and Rickera does not range that far East.

Both Rickera sorpta and Kogotus nonus are known from CA, but we don’t know the complete distributions for each, only that they likely overlap. We have several nice populations of Rickera here in Butte and Plumas Counties which we’ve been studying for many years, so we have adults and associated final instar nymphs. Otherwise, the nymph pigment patterns are so similar between the two taxa, we can’t reliably separate specimens without having reared or carefully associated nymphs from the same location as live-caught adults.

For this specimen, I’d recommend leaving the ID at Diploperlini or using the “slash ID” of Kogotus/Rickera. I know this is not a satisfying determination, but to place this specimen to species would basically be a guess without associated adults. Speaking of which, I’d suggest watching for adults or attempting to rear out nymphs to make the species association. I can't recall whether you've been rearing aquatics, but if not, either John or I would be glad to give you some pointers on a very easy and efficient rearing method for stonefly nymphs.
… Brady Richards, 29 April, 2016 - 1:43pm