Sunday, August 24, 2014

A new one in Montana: the Perlodid stonefly, Kogotus

This is one that we don't get to see in the East: the Perlodid stonefly, genus Kogotus (K. modestus and K. nonus are both found in Montana).  I was totally stumped by the ID, so I did what we should always do with a new stonefly -- I keyed it out, using Stewart and Stark's Nymphs of North American Stonefly Genera (pp. 361-364).  The lack of thoracic gills, the unidentate lacinia, the lack of dark longitudinal bands on the abdominal segments, and the absence of a "transverse anterior suture" on the mesosternal Y-ridge, led me to Kogotus (pp. 413-416).

Let's note certain key features.  1) "Head with light M pattern anterior to darker M between antennae; light spot in ocellar triangle and 2 small light spots outside lateral ocelli."  Check.

2) Lacinia unidentate.  Yes.

3) "Pronotum light, encircled with brown band except light lateral margins; a few tiny marginal spinules, but mostly glabrous."  All easy to see in this photo.

4) "Y-arms of mesosternum meet posterior corners of furcal pits; no transverse anterior suture connecting furcal pits."  Yes.

And one more thing.  5) "Male and female 8th abdominal sterna with mesoposterior interruption of posterior setal row."

The Northwestern Perlodid stonefly, genus Kogotus.  I'll let you know if I'm successful in getting this down to the level of species -- but there are only two choices: nonus and modestus.


The other stonefly I found -- and photographed -- is one that I've found once before: Oregon, August, 2012 (entry posted on 8/22).  The common stonefly, Calineuria californica.

This Perlid is attested in Alberta, British Columbia, California, Idaho, Montana, Oregon, and Washington.  (See Stewart and Stark, p. 329)

A quick review of critical features.  (All quotes from Stewart and Stark.)  1) "Body 17-25 mm, dark brown patterned with yellow."  This immature nymph was just 17 mm.  2) "SL gills (subanal gills) absent."  We can see that in the photos.  3) "Lacinia bidentate, terminal tooth strongly curved."  Yes.

4) "Dorsum of body covered with fine, dark clothing hairs and scattered short, thick bristles."  Yes.

5) "Occipital setae scattered near postocular fringe but arranged in a close set row behind ocelli."  Also, "Head with pale, oval spot surrounding lateral ocelli."  Both features are clear in this photo.

Common stonefly, Calineuria californica.


And one more insect -- sort of.  I was hoping to get a live photo of an "October Caddis" -- the Northern case-maker, genus Dicosmoecus.   Every case that I found, save one, was sealed up with the larva in pupation.  (In Montana, the "October" caddis tends to hatch in November.)  But in the Blackfoot River, I did find one that was open.

This is a large caddis: the case was 25 mm.  But, I could not get the larva to come out of its case!  Maddening.  And I waited a very long time.  To see it, I had to preserve it.  And here it is.

Wiggins' description reads as follow.  "These larvae are large and stout-bodied; sclerotized parts of the head and thorax are mostly uniform dark brown to black."  For sure.  "The tibiae of all legs have several pairs of stout spurs

and there are metanotal setate on the membrane between the primary sclerites."

Finally, "On segment IX a band of 20-40 setae extends ventrad from each side of the dorsal sclerite."  I didn't count them, but 20-40 seems right.

On the case, Wiggins notes, "Final-instar larvae have a case of fine gravel, regular in outline, slightly curved, and often somewahat flattened."  Like the case in the photo above.  "In the early instars cases are largely of plant materials."  You might recall that I found one of those immature larvae in such a case in Oregon in May.  (See post of 5/1/14.)

All quotes from Glenn B. Wiggins, Larvae of the North American Caddisfly Genera, University of Toronto Press, 1977.)

I wish I could have found time to get some more photos of insects: the streams that we fish are healthy with good populations.  Unfortunately, the trout fishing just got in the way!  Below, an 18" "cutbow" (Cutthroat and Rainbow hybrid) from the Upper Clark Fork.  What a beauty!

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