On my trip out to Portland, OR last week I had hoped to spend a full day looking for stream insects and getting good photos. My family had other plans! So, I managed an hour at "Camp Creek" at the base of Mt. Hood. And, it was late afternoon, and we were in a low light situation. So, no live photos to look at -- I had to study my insects this morning using what I could preserve.
Still, since I found a new (for me) genus of the common netspinner caddis (Hydropsychidae), and a new Perlid (common stonefly) genus, it may be worthwhile to look at how we go about genus ID using our keys. So...
1. Hydropsychidae (common netspinner), genus Parapsyche
This is the best I could do for a microscope photo -- but the colors are pretty much on the mark. The larvae I saw were all dark brown, and they were BIG (probably 10-12mm). This is a genus that can be found in the East, but I've never seen it in the streams that I sample. It is apparently confined to small, cold, mountain streams.
Genus ID turned out to be fairly easy. Let me use the options posed in Merritt, Cummins and Berg (2008), p. 491.
1. Genae of head capsule completely separated by single ventral apotome
or
1'. Genae touching ventrally, separating vental apotome into anterior and posterior parts.
Let's have a look.
The genae are completely separated. That means the genus is either Arctopsyche or Parapsyche. Here's the relevant couplet to help us decide.
4. Most abdominal segments dorsally with tuft of long setae and/or scale hairs on each sa2 and sa3 position; ventral apotome of head usually nearly rectangular. ... Parapsyche
4'. Most abdominal segments with single long seta in each sa2 and sa3 position...ventral apotome narrowed posteriorly. ... Arctopsyche
The ventral apotome is "nearly rectangular," and there are indeed tufts of long setae on the sa2 and sa3 positions on each abdominal segment. Those positions are pointed out in the picture below.
If there is any doubt about the shape of the ventral apotome, here is a picture of the ventral apotome on an Arctopsyche nymph found in Montana in August. Note how it narrows from top to bottom.
I might also note that I've never found an Arctopsyche nymph that is not this shade of green.
2. Common stonefly (Perlidae), genus Doroneuria
I'm so disappointed that I could not get a live shot of this nymph! Perlid head patterns are so nice to see.
Genus ID of this nymph proved to be a bit of a challenge until I looked at Stewart and Stark's Nymphs of North American Stonefly Genera (p. 335). For "Diagnostic Characters" they note two key things that we have to find: "(1) occipital setal row complete behind ocelli but interrupted laterally, and (2) dorsum of body with median, longitudinal row of fine, silky setae." Both features are clear from microscope photos.
1) occipital setal row which does not extend to the sides of the head
2) the fine setae on the abdominal terga
Merritt, Cummins and Berg (p. 325) add another feature that we can see: "Ab7 sternum [abdominal segment 7, ventral side] usually with incomplete posterior fringe." No question about it.
Doroneuria is not a genus that occurs in the East. Look for this one mainly in the pacific northwest -- Oregon, Idaho, Washington and Montana. Its existence is also attested in California, Nevada and Wyoming.
So, not the bonanza of bugs I was hoping to find and not the photos I was hoping to get. Better planning will be required for my next trip to Oregon to see my daughter!
(Below: the sun filters through the dense vegetation of the forest surrounding Camp Creek.)
No comments:
Post a Comment