Hiding in Plain Sight

…would be a suitable title for any of the posts about tiny bugs that I regularly write here, I guess, but it seems especially appropriate in this case. The story begins in September 2012, when occasional BugGuide.net user Greg Dodge posted this photo of blotchy white leaf mines on white clover (Fabaceae: Trifolium repens) he found in Durham, North Carolina. They didn’t seem to match any mines known from this common plant, so the few of us who pay attention to such things were intrigued. He put them in a vial, and eleven days later, he posted photos of the adult moths that emerged. The moths appeared to be Porphyrosela desmodiella (Gracillariidae), a relatively straightforward identification since this was the only species of Porphyrosela in North America. Here is an adult of P. desmodiella that I reared from its namesake, Desmodium (tick trefoil), in Arizona (also in the fall of 2012, as it happens).

Here is the leaf mine on Desmodium, as viewed from above and below:

This is a typical “underside tentiform” mine, which starts as a flat blotch on the lower leaf surface, then the larva spins  silk inside it, which contracts as it dries and causes the leaf to buckle and form a “tent”.  Porphyrosela desmodiella is known to mine leaves of several legumes in addition to Desmodium, so it didn’t seem out of the question that it should mine clover leaves on occasion. The problem was, P. desmodiella always makes underside mines, whereas these clover mines were on the upper surface.

After I moved Greg’s photos to the Gracillariidae section for further contemplation, he commented: “The adult moth seems to be Porphyrosela desmodiella. The question is, why is the mine, or tent, that I photo’d different from what is described for this species here on BugGuide, that is, on the upper surface of the leaf not the underside? Although I found several spent pupal cases attached to the vial in which the moths were raised, I did locate one within one of the curled up leaflets. Interestingly, I found this site with a photo of a tent which looks remarkably like the one that I photo’d but which belongs to Porphyrosela minuta from southern South America. Anybody?”

Porphyrosela minuta was described in 1953 from specimens reared from white clover in Argentina. The paper Greg found documented the life history of this moth on white clover in Uruguay. It is not known to use any other host, which is odd since the moth is apparently native to South America and the plant is native to Europe (where no species of Porphyrosela are known to occur).

Terry Harrison quickly responded that it would be great if Greg could send the specimens to Don Davis at the Smithsonian so that he could examine them. Alas, Greg reported that “they all flew off except one which was unfortunately, and unintentionally, spread across the inside of one of the vials. I may try to rear more.”

Two months later, Thomas Wilson posted photos he had taken of similar leaf mines in Baltimore, Maryland, a few weeks before Greg found them in North Carolina. When Thomas left a comment on Greg’s post pointing this out, Greg replied: “I had planned on shipping off a specimen of an adult to Don Davis for identification but the only specimen that I had was a smashed individual that was later eaten by a roach (my fault completely, I left it sitting around too long in a vial with the lid partially open). I tried to rear more but was unsuccessful. Maybe next season.”

Nothing more was said about the subject for three years. Suddenly, in August 2015, these Porphyrosela mines on white clover were found by Domingo Zungri of Roseville, California; Mike Palmer of Stillwater, Oklahoma; and Tracy Feldman of Durham, North Carolina. I encouraged them all to collect lots of mines, not wanting to hear any more stories about the one(s) that got away or were smooshed and then eaten by roaches. I also told my friend Eric LoPresti at the University of California (Davis) to keep an eye out for them. Mike, Tracy, and Eric all came through; Tracy also found them where he teaches in Laurinburg, not far from the South Carolina border, and although Eric didn’t see any in California, he happened to be in Durham that month and stuffed a sandwich bag full of the mined leaves.

As a result, Porphyrosela minuta is now properly documented in North America. Voucher specimens are deposited at the Smithsonian and in the Canadian National Collection, and our paper* was published in January. (The print version finally showed up in my mailbox yesterday, which reminded me that I should write this post.)

When J. F. G. Clarke described Porphyrosela minuta as a new species, he stated that it was extremely similar to P. desmodiella, and apart from details of the genitalia, the only difference he noted was that P. minuta has a black terminal line on the forewing that P. desmodiella lacks. His description was based on a single male and four females. With several times that many specimens in front of me, I noticed another difference in the wing patterns of the two species. In the reared examples of P. desmodiella I examined, the second fascia (stripe) on the forewing was approximately perpendicular with the wing margins, bending somewhat so that it paralleled the first fascia toward the costal margin (the bottom of the wing when a live moth is at rest). The space between the fasciae along the costal margin was about 20–30% larger than on the dorsal margin. In contrast, on P.
minuta the first and second fasciae are angled equally but in opposite directions, so that the space between them on the costal margin is about twice that on the dorsal margin.

That may sound like a subtle distinction, but take a look at the two side by side and I think you’ll see (P. desmodiella above, and P. minuta below):

The black markings are much bolder on this P. minuta than on this P. desmodiella, but unfortunately this doesn’t seem to be a consistent difference, and that also goes for the terminal line mentioned by Clarke. The difference in the angling of the second fascia, on the other hand, seems to be entirely consistent.

Although I’ve now coauthored several new insect species, I have always just contributed the parts about the larval biology and natural history, so finding this difference sort of felt like my first real foray into taxonomy. Having made this little discovery, I took a look at the photos of Porphyrosela desmodiella on BugGuide.net, and was surprised to find that all of them—with the sole exception of one that MJ Hatfield had reared from an underside tentiform mine on Lespedeza (bush clover) in Iowa—were in fact P. minuta! Once I realized this, it turned out that the first photo of P. minuta in the US was this one of an adult found in Louisiana in June 2008. Tracy remembers seeing the mines and an emerging adult sometime between 2000 and 2002 in the same lawn in Durham, NC, where Eric collected them in August 2015, but he was unaware of their significance at the time.

So is this some terrible new invasive species that has swept across the country? I don’t see why anyone should be bothered about it; there’s plenty of clover to go around, and clover isn’t native either. And the leaf-mining larvae are providing food for at least three species of parasitoid eulophid wasps, which as far as I know are all native:

Hemiptarsenus sp.

Sympiesis sericeicornis (I’ve reared this one from P. desmodiella as well)

Pnigalio coloni

As far as I’m concerned, anything that increases the biodiversity of lawns—an all too dominant feature of our landscape—is a good thing. I’ll be curious to hear if anyone finds these clover leaf mines anywhere else in the US. Right after our paper was published, I heard from someone in southern Brazil that P. minuta has been found there as well, for a total of three adjacent South American countries, plus the five scattered states in the US mentioned above, where this moth is known to occur. I would love to know what its original host plant was in South America, and how it managed suddenly to become established from coast to coast in North America before anyone noticed it.

* Eiseman, Charles S., Tracy S. Feldman, Eric F. LoPresti, and Michael W. Palmer. 2017. First North American records of Porphyrosela minuta Clarke (Lepidoptera: Gracillariidae), with notes on its native congener, P. desmodiella (Clemens). Proceedings of the Entomological Society of Washington 119(1):18-23.

About Charley Eiseman

I am a freelance naturalist, endlessly fascinated by the interconnections of all the living and nonliving things around me. I am the lead author of Tracks & Sign of Insects and Other Invertebrates (Stackpole Books, 2010), and continue to collect photographs and information on this subject. These days I am especially drawn to galls, leaf mines, and other plant-insect interactions.
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