Sunday, March 31, 2019

Another new insect: an Ameletidae, Ameletus tertius

I found this little mayfly at the Rapidan River on Tuesday, and when I looked at it in the bowl, my first guess was that it was nothing but the small minnow mayfly, Baetis intercalaris.  Still, something wasn't quite right.  It was only when I focussed in to get some photos that I realized this was something I'd not seen before.  By the shape of the head, the short antennae, and the fact that the gills pointed straight up and down -- sort of like the oar blades on a crew boat -- I knew that it was Ameletidae,  but what species?

When I got home I looked at Steve Beaty's descriptions ("The Ephemeroptera of North Carolina," p. 1) in which five different species are keyed out for this part of the country -- cryptostimulus, lineatus, ludens, tarteri, and tertius.    The A. tertius description caught my eye for one prominent reason: "distinctly marked small species with dorsal terga 3-6 with two large, ovalized submedian segments" (Beaty, p. 1)  Bingo!

And another feature shows up in this photo as well -- "tarsi with both dark basal and apical bands." (Beaty)

But there were two other features that required some microscope work: 1) "ventrally pale except sterna 9 and 10 darkened (also sometimes a portion of 8)," and 2) "posterior spinules on abdominal terga 1 or 2-10."

Yes in both cases (though I realize it may be difficult in my photo to see the spinules except for those on segments 5 and 6, they were present on all of 2-10.)

Score again for the Rapidan River -- Ameletus tertius!  Here's some more photos.

Sometimes I wonder why I go to other streams.

A. tertius is the fourth Ameletidae species I've found.  The others,

Ameletus cryptostimulus,

Ameletus lineatus,

and in Montana, Ameletus subnotatus.

Wednesday, March 6, 2019

Ironoquia punctatissima: a new caddisfly casemaker in a small stream in Sugar Hollow

Yesterday afternoon, I went with a friend to a tiny stream in Sugar Hollow, one in low-lying ground.  It was shallow and slow-moving, just a couple of feet wide, but there were some small riffles here and there and the occasional leaf pack.  To our surprise, we saw a fair number of insects including this casemaker which turned out to be Ironoquia punctatissima (Limnnephilidae).

Two things were clear from the very beginning in terms of key features: for one the case was rounded and slightly curved, seemingly made out of rows of pieces of bark, and secondly, the gill tufts were multi-branched.  Take a close look.

Leafing through Wiggins -- Glenn B. Wiggins, Larvae of the North American Caddisfly Genera (Trichoptera) -- I found what looked to be a pretty good match in the Limnephilidae genus, Ironoquia, so that's where I began. (pp. 249-249 in the 1977 edition)  On the genus morphology, Wiggins wrote the following things: "Ironoquia, one of four North American limnephilid genera in which most abdominal gills of the dorsal and ventral rows have more than four branches, is distinct from the others in having more than two (usually five) major setae along the ventral edge of the middle and hind femora.  Many metanotal setae arise from the integument between the primary sclerites.  Length of larva up to 22 mm."  All of this worked out to be perfectly true.  Here are the key microscope photos.  (And this larva was about 18 mm.)

For additional confirmation, we can look at what he says about the type of case and the habitat in which this genus is found.

"CASE  Two types of larval case are known.  In I. punctatissima and I. lyrata cases are made of bark and leaves, curved but little tapered; the case of I. parvula is made of sand grains." (p. 248)

"BIOLOGY Although North American larvae of the subfamily Dicosmoecinae are largely restricted to cool, running waters, species of Ironoquia are the sole exception, living in temporary pools and streams." (p. 248)

Beaty says much the same on the habitat of this genus: "Found in temporary streams as well as swamp streams." ("The Trichoptera of North Carolina," p. 82)  I have no problem thinking that this was a temporary stream, one that dries up in dry summers.

What about the species?  For this I had to turn to the new book by Morse, McCafferty, Stark, and Jacobus -- Larvae of the Southeastern USA: Mayfly, Stonefly, and Caddisfly Species (Clemson University, 2017).  They note, and illustrate, two possibilities: punctatissima and parvula. (pp. 392-393)  The difference between the two has to do with the head and nota.  For Ironoquia punctatissima -- "Head and nota pale with dark spots and infuscations" (p. 392): and for Ironoquia parvula -- "Head and thoracic nota dark with pale central stripe" (both types of head are illustrated on p. 393)  No doubt about it, we've got a head that is pale with dark spots.

Ironoquia punctatissima -- so much fun to finding something new.

We also found a mayfly that might be a new species for me -- Eurylophella funeralis.

But these little nymphs are hard to get down to the level of species.  To do that, we need a clear look at the abdominal tubercles, and the two nymphs we found yesterday were dirtied up with detritus.  (Sigh.  I wish someone made a tiny, tiny brush that we could use to clean these guys up!)  (:

In any event, we really enjoyed taking a look at this stream, and you can be sure we'll work on it more in the near future.