Today I reached a major milestone in my leafminer book project: I’ve now made keys to the known leaf mines on every plant genus in the US and Canada. To do this, I had to review the published natural history information for 35 sawfly species (one of which I co-described last year), 200 beetle species (three of which were just described in the most recent issue of the Coleopterists Bulletin, in addition to the Orchestomerus species I discussed in my last post), over 500 fly species, and over 1000 moth species (these last two groups have many more described species that are almost certainly leafminers but have never been associated with any host plant). I include these parenthetical asides to highlight the fact that this project can never really be finished, because more species and life histories are being discovered all the time. But I’ll consider it to be time to start looking into publishing this thing when I’ve finished writing all the introductory chapters, which could conceivably happen by the end of this winter.
The last keys I wrote, after finishing all the graminoids (grasses, sedges, and rushes), were the ones for all the conifer needleminers. I was dreading these all along, because I didn’t think there could be much variation in needle mines and wasn’t sure how I could construct keys to them. But luckily T. N. Freeman spent over 30 years studying needle-mining moths and made some keys in the 1960s that I was able to build on. It was actually sort of fun working out how, for instance, 30+ species of moths might be distinguished by their idiosyncratic styles of living inside pine needles.
So I thought I’d celebrate by sharing photos of a couple of conifer needleminers from my own front yard. As shown in the photo at the top of this post, when Julia and I first moved here there was literally nothing in the front yard except for a lawn and an arborvitae (a.k.a. northern white cedar, Thuja occidentalis) hedge along the road. Five species of moth are needleminers on Thuja, and so far I’ve found two of them in our hedge. The mines all look pretty much like this:
If you backlight the mines from our hedge, you can see that they are all nice and clean-looking because the larva (which is curled into a “J” in the photo below) has been pushing all of its frass out of a hole at the tip.
Only two of the five arborvitae miners are fastidious in this way, and they can be distinguished by the color of the larva.
Since this larva is brown, we know it’s Coleotechnites thujaella (Gelechiidae). I raised some adults this spring, and when I took one out to the hedge to get a natural-looking photo of it, I found lots of them hanging out on the foliage already.
A number of Coleotechnites species can only reliably be distinguished by the habits and host plants of their larvae. When I sent one of these adults to Jean-François Landry to confirm that it was C. thujaella, he annotated my tentative identification with “reasonable id BUT others possible.” At this point, no other Coleotechnites species is known to feed on Thuja, so I’m going with that ID until someone comes up with a reason to question it. In terms of wing pattern, there are probably more differences between the two individuals above than with some individuals of other species of Coleotechnites.
Along with the Coleotechnites adults, there were a number of these hanging out on the hedge at the same time:
This is Argyresthia thuiella (Argyresthiidae), a member of a family that has been given the common name of “shiny head-standing moths.” It happens to be the other species that makes nice, clean, frass-free mines on arborvitae. Its larvae are green instead of brown, and I didn’t happen to notice any last spring, but theoretically I should be able to find some right now, since these needleminers all overwinter in their mines.
In the process of rearing the Coleotechnites larvae, I also had a bunch of tiny (1 mm) parasitoid wasps emerge, all in the family Encyrtidae. To my knowledge no one has ever suggested a common name for encyrtids, but they’re a good deal shinier than “shiny head-standing moths,” for whatever that’s worth.
Copidosoma lymani (female).
Copidosoma lymani (male).
Copidosoma bucculatricis (male).