In my previous post, I mentioned having found a couple of leaf mines that needed a little more investigation to decide whether they’re something new for this year’s yard list. Well, I investigated, and they are!
Leafminer #197: Stigmella sp. (Nepticulidae), on paper birch (Betulaceae: Betula papyrifera). On September 27 I plucked a leaf with three narrow linear mines on it from the paper birch sapling at the southeast corner of the yard. I’ll show each of them in top, bottom, and backlit views. Here’s the first one:
The egg was laid next to a prominent vein on the underside of the leaf (lower left corner of the third photo above), but the mine is initially confined to the upper surface, following the vein (first photo above); later it becomes full-depth, visible on both leaf surfaces. The second mine follows the exact same pattern (note the eggshell in the upper left corner of the third photo below):
The third one starts out the same way (note how it starts out following a vein from the right edge of the first photo below, originating from an egg visible at the left edge of the third photo), but then it becomes a mostly lower-surface mine, with a few little full-depth patches.
The little dots of external “window feeding” on the underside of the leaf next to the third mine initially led me to think these were Bucculatrix mines (both birch-feeding Bucculatrix species form short linear mines that they exit to window-feed on the leaf surface), until I saw that all three larvae were still in their mines and realized this feeding sign was from some other insect. The round eggshells and the appearance of the larvae identify these miners as moths in the family Nepticulidae. Consulting the key I wrote to the known North American birch leafminers, I see that a linear mine like this could be the work of one of seven species, but I can rule out the three species of the Stigmella betulicola group because they have distinctly yellow larvae. This leaves two species in the S. lapponica group that are also known from Europe, plus an undescribed Stigmella in the lemniscella group and Ectoedemia quadrinotata, both of which I’ve already found in my yard this year (on black birch and hazelnut, respectively). All four of these have pale larvae like the ones in this leaf. Stigmella lapponica can clearly be ruled out because its mines are initially filled with green frass, whereas these mines have a black central frass line in the early portion.
Two days after I collected the leaf, all three larvae had exited their mines to spin cocoons. Here are backlit views of the completed mines:
Each of these mines is only about 0.5 mm wide at the end—probably the narrowest completed nepticulid mines I’ve seen on any host plant—and in each case the larva exited through a slit on the lower leaf surface. These mines are far too small and narrow for Ectoedemia quadrinotata, which I was already inclined to rule out because the larva of that species has a dark central spot on each segment that should have been visible in my photos. They are also too narrow, and the frass pattern is all wrong, for the undescribed species in the Stigmella lemniscella group. This leaves S. confusella, which is only known from Manitoba outside of Europe. Although that species likewise lays its eggs next to veins on the lower leaf surface, it is said to form “a very long and slender mine, with frass in a continuous, very narrow, central line. The mine follows veins over long distances, giving it an angular appearance.” These mines are certainly slender, but they are by no means “very long”; the frass tends to fill the later portion of the mine; and each only follows a vein at the beginning. They bear little resemblance to the examples shown on the European leafminer website. This is why, when using a key, it’s important not to just accept whatever identification you land on at the end. You should always read the accompanying description and consult whatever illustrations are available to make sure everything fits.
So what species have I got here? I dunno. Some other Stigmella, I guess. Another undescribed species? A European species not previously documented in North America? I look forward to hearing what Erik van Nieukerken has to say about these.
Leafminer #198: Ophiomyia carolinensis (Agromyzidae), on smooth aster (Asteraceae: Symphyotrichum laeve). Weeks ago I had noticed a mine of Acrocercops astericola (Gracillariidae) on this aster growing by the mailbox, and I for a while overlooked the O. carolinensis mine a few leaves up the stem from it because it was superficially similar. I had a nagging feeling about it and finally got around to taking a closer look yesterday. The way the mine alternates between leaf surfaces is characteristic.
Leafminer #199: Phytomyza crassiseta (Agromyzidae), on speedwell (Plantaginaceae: Veronica sp.). Julia and I noticed a few of these mines yesterday when we peeked under the ostrich ferns growing along the side of the garage to look for one of the little leatherwood shrubs we’d planted last year (it turned out a vole or rabbit had recently cut the stem off at the base for no discernible reason).
A backlit view shows the two puparia hidden on the lower surface, each with a longitudinal stripe on its belly:
Last night there were strong winds that woke us up in the middle of the night and made us wonder for a little while if we should go seek shelter in the basement. This afternoon I spent some time picking up branches that had blown all over the front yard, mostly from the big poplar tree at the south edge of the yard.
As I’ve been tallying the leafminers and sawflies in the yard throughout the year, I’ve been looking on this tree with a bit of scorn because it never seems to have any bugs feeding on it. It’s a weird tree that I’d never gotten around to trying to identify before today; it clearly was planted by the previous owners at the same time as a bunch of other oddball trees that are all smooshed together there at the edge of the yard: a silver maple, a pin oak, a pitch pine (which finally died in the past year due to competition with its neighbors), a European larch, and several nonnative spruces (a few of which we cut down several years ago to let some more light into the yard). After checking two botanical manuals, it seems to be Populus × canadensis, a hybrid between the native eastern cottonwood (P. deltoides) and the European/Asian/African black poplar (P. nigra). Today this tree finally started pulling its weight.
Leafminer #200: Aulagromyza ?populicola (Agromyzidae). Just after throwing a big branch on the brush pile, I noticed this mine on the underside of one of the leaves.
A close look at the backlit view below reveals the tiny puncture where the egg was inserted in the leaf; the scattered, fine specks of frass; and the two rows of meconial pillars arranged by a eulophid wasp larva after devouring the fly larva from within. The emerging adult wasp chewed a round exit hole in the lower epidermis between the two rows of pillars, which served to protect the wasp’s pupa from potential collapsing of the mined leaf tissue as it dried.
Aulagromyza populicola is a European species that has been found in Ontario and Oklahoma; this mine was either made by that species or something unknown but presumably closely related (A. populicola is not known to make lower-surface mines, which I’ve found before on cottonwood and bigtooth aspen in South Dakota, Kansas, and Massachusetts).
Leafminer #201: Stigmella populetorum (Nepticulidae)… or another, closely related species in the S. salicis group. I spotted this mine on the lower surface of a leaf on a twig that had blown all the way across the yard and onto the driveway.
Although at first glance this looks like another irregular whitish mine similar to the Aulagromyza one, the egg in this case is deposited on the leaf surface instead of inserted; the mine is initially narrowly linear; and the frass is in a continuous dark line (as in the Stigmella on birch).
Leafminer #202: Phyllocnistis populiella (Gracillariidae)—yet another lower-surface mine, this one on a big branch that landed on the hugelkultur bed. This superficial mine is formed just in the epidermal cells, and it appears silvery or nearly invisible depending on the angle of the light.
Leaf (stem) miner #203: Marmara fasciella (Gracillariidae), on the white pine (Pinaceae: Pinus strobus) sapling at the edge of the leach field. I’m pretty sure I checked this sapling back in the spring when I was on a roll with finding Marmara mines in the yard, but somehow I missed this mine, which clearly has been there all along.
I don’t expect to add too many miners to the yard list in the remaining three months of the year, but you never know…