Wednesday, December 17, 2014

All the evidence we're going to need: That's Acroneuria lycorias in Buck Mt. Creek

I expected to see winter insects today at Buck Mt. Creek -- and I did: small winter stoneflies, large winter stoneflies (still very tiny), Clioperla clio (only one), Uenoids, and Glossosomatids (Saddle-case makers).  But everything that I saw was covered in silt after heavy rains yesterday.  So, I didn't take a whole lot of pictures.

However, I did find three more Acroneuria lycorias/carolinensis nymphs (look back to the previous entry), so I had a chance to test out my theory.  I argued last time that the A. lycorias differed from A. carolinensis in two different ways: 1) yes, they have anal gills while carolinensis do not, and 2) vs. carolinensis, they lack medial markings on the terga (dashes, a stripe).  All three of the nymphs from today can be used for support of that thesis.

The biggest of the three: 16 mm.

Take a close look at that photo.   No need for a microscope to see the anal gills on this baby, and there are no medial markings.

Here's one that was smaller.  But you can still make out the gills, and note that the tergal bands are fairly regular, something we noted last time.

Beaty does not use the lack of medial marks/stripes to distinguish lycorias from carolinensis.  Have to pass this data along and see what he thinks.

One other insect of interest this morning: the small case-maker Apatania incerta, one that I don't find very often.

Terrible photos -- best I could do.  Still, we can see the features that are characteristic.  1) the case is "cornucopia" shaped with a hood at the top that covers the head of the larva as it's crawling along; and 2) the larva is yellow in color.  But "proof" requires a microscope view.

The front edge of the mesonotal sclerites are straight across -- vs. those of the Uenoids which are "emarginated."  And there are no sa1 sclerites on the metanotum: in their place we find a setal row:   ("anterior metanotal plates replaced by row of about 20 setae" (Beaty, "The Trichoptera of North Carolina," p. 85.)

I'll be seeing totally different insects on Friday: off to one of my favorite small streams in Sugar Hollow.

(P.S.  Steven Beaty confirms that there seems to be something to the correlation we've noted: presence or absence of anal gills, presence or absence of medial, abdominal markings.  How about that?  We may be on to something.)

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