The day after I wrote my last post, in which I discussed an oak leafminer I’d previously mistaken for Stigmella nigriverticella and mentioned that I’d been keeping an eye out for leaves with “green islands” blowing onto my driveway from the quaking aspen across the road, I found a couple of leaves that require me to follow up on both of those stories.
Leafminer #206: Ectoedemia sp. (populella group) (Nepticulidae), on quaking aspen (Salicaceae: Populus tremuloides). The storm on October 16 brought the leaf I’d been waiting for:
I wrote about these mines five years ago, but I’ve done some further investigation since then, which is reflected on pp. 1129–1130 of Leafminers of North America. To summarize, there are two species in North America that make identical mines on aspen leaves. The egg is laid on the petiole and the larva mines from there into the base of the leaf blade, where it forms an elongate blotch with frass along the sides. The area surrounding the mine remains green after the rest of the leaf has turned yellow, and the larva continues mining within this green patch after the leaf has fallen to the ground. One of the species that does this is Ectoedemia argyropeza, which is introduced from Europe and is now one of the most common nepticulids in northeastern North America. The adult looks like this:
The other species doesn’t have a name yet. The only reared specimens in existence came from a single tree about a mile down the road from my house, but their DNA matches that of adult moths caught in Alberta, Saskatchewan, and Manitoba. The adult of this undescribed species looks like this:
It is not a Stigmella, as Erik van Nieukerken initially thought based on the above photo; it is an Ectoedemia in the populella group (along with E. argyropeza and E. populella). And although I pointed out some apparent differences between the mines of these two species in my post from five years ago, more recently I collected 100 mined leaves from that same tree and carefully scrutinized each one to make sure the mine characteristics were consistent with those of E. argyropeza. The following spring, dozens of E. argyropeza adults did emerge (including the one in the first photo above), but then a few days after the last one emerged, a dozen or so adults of the undescribed species emerged. So unfortunately it seems that identifying these “green island” aspen mines to species requires either DNA analysis or rearing adults.
Back to the leaf I collected in my driveway four days ago, here’s a view showing the eggshell (far left) and the initial mine in the petiole leading into the blade:
Here’s a backlit closeup showing the small blotch mine within the green island. Nobody seems to be home…
…but these larvae are mostly nocturnal, hiding in the petiole during the day. In the photo below, taken this evening, you can see the larva munching away.
Leafminer #207: Stigmella nigriverticella (Nepticulidae), on red oak (Fagaceae: Quercus rubra). The real one this time. I think I had noticed this mine before (in the shrubby area between the main yard and the “nut orchard”), but had ignored it since I knew I’d already put S. nigriverticella on the list.
I of course have no idea at this point what the adult of the S. nigriverticella imposter looks like, but here is the actual S. nigriverticella reared from the mine on Nantucket shown in my previous post:
Over the weekend I put all of my rearing containers in the little fridge in the basement so I can forget about them for a few months. I checked them all one last time before doing so, and I found two adults of sawfly #41 from pussy willow—a female from one of the hatchlings I’d collected on August 31 (all of the larvae matured and burrowed into soil by September 15)…
…and a male from one of the eggs I’d collected on September 2 (all of those larvae burrowed into soil by September 18).
I also got one last parasitoid for the season, a eulophine eulophid from a Cameraria betulivora mine in a black birch leaf I’d collected on September 27.
Today I was wondering what was going on with those late-emerging sawflies. The vast majority of sawfly species overwinter as prepupae, and I don’t know if any overwinter as adults. But surely there isn’t enough time for another generation to develop before all the willow leaves are gone? I wandered over to the pussy willow shrub that had already endured two generations of sawfly #9, followed by three waves (if not distinct generations) of sawfly #41, the last of which attracted a number of ichneumonids. I didn’t see any activity on the few remaining leaves, but without the distraction of all those sawfly larvae, I noticed for the first time something that had been there all along:
Leaf (stem) miner #208: Marmara salictella (Gracillariidae). This is the type species of Marmara, described from Pennsylvania by J. Brackenridge Clemens in 1863, and one that I haven’t had the opportunity to rear yet. Something to keep an eye on next spring!