Fringed loosestrife (Primulaceae: Lysimachia ciliata) is a common plant of moist areas that, I realize now that I’m starting to write this post, I’ve never bothered to photograph. But it has yellow flowers and is related to garden loosestrife; it has nothing to do with purple loosestrife (Lythraceae: Lythrum salicaria). Anyway, five years ago—on September 22, 2015—I was at work doing some botanical something-or-other in a Massachusetts wetland when I noticed what appeared to be leaf mines on fringed loosestrife.
It took a very close look at the lower leaf surface to determine that they were in fact what I call “pseudomines”: rather than feeding between the two leaf epidermises—the definition of leafmining—the larva was feeding externally on the underside of the leaf, but beneath a sheet of silk that to the naked eye appeared to be the loosened lower epidermis of the leaf.
There was a twist though: although the “blotch” in the leaf blade was a pseudomine, the larva was also making a bona fide tunnel in the midrib. The entrance to this tunnel is visible at the left end of the pseudomine in the photo above; in the backlit photo below, the excavated portion of the midrib is transparent, and you can see the larva inside the midrib at the left end of this tunnel.
I tried to rear these larvae to find out what they were, and they eventually transitioned to feeding between leaves that they tied together with silk. I took photos of two of the larvae a month after I collected the leaves, on October 22.
Whether the differing appearance of the two larvae (e.g., the second one has darker spots and a dark prothoracic shield) indicates two different instars or just individual variation, I don’t know. By November 1, at least one of them had spun a silken chamber…
…which I suspect was a shelter in which to overwinter, rather than a cocoon in which to pupate. I don’t remember if any of the larvae survived the winter, but the photo above is the last one I have from this rearing.
This mystery has been bugging me ever since, compounded by my suspicion that this moth may be what V.T. Chambers described as Lithocolletis lysimachiaeella (Gracillariidae) in 1875*. The entire description of that species reads:
The larva is cylindrical and very small. It makes a very small tentiform mine on the under side of the leaves of (Lysimachia lanceolata) the loosestrife. The imago is, no doubt, very small—probably not larger than L. desmodiella, Clem., which is the smallest known species of this genus; but I have not succeeded in rearing it.
He gave no indication of where or when he found these larvae, but it was presumably near his home in Kentucky. When she revised the genus in 1908**, Annette Braun noted that she had never seen a Lithocolletis mine on Lysimachia**, and the species was essentially never spoken of again—until Brower (1984)*** made the baffling claim that three specimens had been reared from beech in Maine. (Some of the obvious misidentifications in his list of Maine Lepidoptera can be attributed to using old keys to identify species that hadn’t yet been described when the keys were written, but what could possibly have led him to believe that this species that was known only from a vague description of a larva was the same one that had been reared from a totally unrelated plant a thousand miles away?) The previous year, Don Davis had listed lysimachiaeella as a species of Phyllonorycter****, but this was based only on the fact that Lithocolletis had been synonymized with Phyllonorycter (though it’s not quite that simple, because Braun’s Lithocolletis subgenera Cremastobombycia and Porphyrosela are now recognized as full genera, and the genus Cameraria—which was named for V.T. Chambers; camera being the Latin word for “chamber”—was designated for “Lithocolletis” species with flat larvae that form upper-surface mines).
There is in fact no reason to believe that what Chambers described was even a gracillariid; just a few years earlier he had dedicated a whole paper to leaf-mining “moths” he had previously written about that had turned out to be beetles*****. There is also a footnote in (I think) one of Lord Walsingham’s papers where he listed some other egregious mistakes Chambers had made in describing new species based only on larvae, but I don’t remember now where I saw that.
Anyway, whether or not my midrib-tunneling loosestrife pseudo-miner is what Chambers called Lithocolletis lysimachiaeella, I’m reasonably sure it’s a moth in the family Tortricidae. A few tortricids in the genus Paralobesia do a similar combination of midrib tunneling and pseudo-mining in leaves of magnolia and tuliptree.
Last fall, on September 17, I found larvae of this mystery moth in Vermont, but I again failed to rear them to adults. I had a hunch that the larvae are immature when they overwinter and resume feeding as leaftiers in the spring, so on May 12 I was excited to see a bunch of tied leaves on the fringed loosestrife growing behind the chicken house.
(The frilly hairs on the petioles, incidentally, are why this plant is called “fringed” loosestrife.) Naturally I stuffed a bunch of these tied leaves in a peanut butter jar to see what the larvae would turn into. Alas, ten days later when I got a look at some of the larvae, I found that they bore no resemblance to the mystery larvae, though they did likewise seem to be tortricids.
At the end of May, the sparkling adult moths began to appear.
Identifying them turned out to be easy. The HOSTS database lists two moth species that feed on Lysimachia ciliata as larvae. One is Nola cilicoides (Nolidae), which I discussed as leafminer #157 in my yard list, and the other is Aterpia approximana (Tortricidae), which is a good match for the moths I reared. Which means, it seems, that nobody knows the identity of the species that was the main subject of this post. There’s always next year, I guess!
* Chambers, V. T. 1875. Tineina of the Central United States. Cincinnati Quarterly Journal of Science 2(2): 97–121.
** Braun, Annette F. 1908. Revision of the North American species of the genus Lithocolletis Hübner. Transactions of the American Entomological Society 34: 269–357.
*** Brower, Auburn E. 1984. A list of the Lepidoptera of Maine–Part 2: The Microlepidoptera Section 2 Cosmopterigidae through Hepialidae. Maine Agricultural Experiment Station Technical Bulletin 114: 1–70.
**** Hodges, Ronald W. (editor). 1983. Check List of the Lepidoptera of America North of Mexico. The Wedge Entomological Research Foundation.
***** Chambers, V. T. 1872b On some leaf-mining Coleoptera. The Canadian Entomologist 4(7): 123–125.