Saturday, November 3, 2012

Another Perlodid stonefly shows up for the new season: Diploperla duplicata

It had to be a quick trip this morning -- pressed for time.  But I decided to look at the Moormans in Sugar Hollow, some place I've not been since the summer.  I didn't see a lot -- Buck Mt. Creek is the only place I'm seeing large numbers of insects -- but I did find my first Diploperla Perlodid stonefly.

I knew right away what it was, by the color -- drab brown -- and the shape of the head.  Still, it was a small one, 3 mm, so I had to do the requisite microscope work so I could be sure.  There are two things to look for on Diploperla Perlodids: 1) the arms of the mesosternal ridge meet the posterior edge of the mesosternum separately (Peckarsky, Freshwater Macroinvertebrates, p. 71), and 2) the "terminal lacinial spine [is] long, 1/2 as long as [the] lacinia."

The arms of the ridge look like this:

The laciniae on Diploperlas look like this:

The lacinia on a Diploperla nymph is bi-dentate (two teeth/spines), and there are no setae/spines on the lacinia below the second tooth.

While I could not get a good photo of the mesosternum on this tiny 3 mm nymph, I was able to get a microscope shot of a lacinia.  Clear enough -- it's Diploperla.

D. duplicata is the only species I've seen in our streams: it's the only Diploperla species that does not have submental gills.

Diploperlas are probably the least attractive of the Perlodids -- at least when they're young.  But as they mature that changes.  We can track how they change in this sequence of photos that I took last season.

1. 11/17/11, the first nymph I found last year.

2. 2/20/12.  The pattern on the head is much more pronounced.

3. 3/28/12.  This one's fairly mature, and you can't say that it's "drab" anymore!

4. 4/24/12.  Fully mature -- and spectacular.  (At maturity, D. duplicata nymphs measure 11-14 mm.)

So, the show's just beginning.

Not much else to show for my hard work today.  I did find some small winter stoneflies, but I think those in Buck Mt. Creek are a bit more mature.

And I found an unbelievably small large winter stonefly -- Taeniopteryx burksi.  It measured 1.5 mm.

1.5 mm, but we can still make out coxal gills!

I'd prefer to find "large" large winter stoneflies: these are a challenge for my macro lens, and my eyes are starting burn from trying to focus!

Diploplera duplicata:

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