Leaf-mining Leafrollers

Today the latest issue of the Journal of the Lepidopterists’ Society arrived in my mailbox, including the second note I’ve written for the journal.  This reminds me that I never wrote a blog post about the subject of my first note, so here goes.  (The paper, incidentally, is now available for all to see, here.)

In March of last year when Julia and I were surveying for leafminers all over Florida, we kept encountering mines on inkberry (Ilex glabra) with all of the frass pushed out of a hole in the lower epidermis, often near the leaf midrib.

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The mines always seemed to be empty, but at St. Sebastian River Preserve State Park, Julia broke open a leaf and found a caterpillar inside.

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We realized that most of the mines were occupied, and the larvae were simply difficult to see through the thick leaves. So we stuffed a bunch of  leaves into some vials to see if we could raise any to adults.

Toward the end of April, a pair of tiny (1 mm) eulophid wasps emerged from one of the mines.

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I sent them to Christer Hansson in Sweden, who confirmed my suspicion that they belonged to the genus Zagrammosoma. He told me that they were definitely not any of the species known from the US, and that they appeared to match the description of Z. velerii, which was described in 1995 from specimens collected in Cuba.

Beginning in early May, eighteen adult moths appeared in the vials.

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They belonged to the family Tortricidae, commonly known as “leafroller moths,” but like the buckeye petiole borers I wrote about earlier, they lived their whole lives without ever rolling a leaf.

In August, while working in eastern Massachusetts (the same job that led me to find a new species of weevil), I found similar leaf mines on winterberry (Ilex verticillata). As I explain in more detail in the paper, I had attributed these to a species of Rhopobota (Tortricidae) in Tracks & Sign of Insects but this was actually more of a strong suspicion than a proven fact. (Lately, in chasing down the sources of contradictory statements in literature about leaf-mining moths, I have found that I am by no means the only person guilty of this offense.)  Wanting to determine the precise identity of this moth once and for all, and to see if it was the same moth we reared from inkberry in Florida, I collected a good number of leaves from two different sites.

Beginning in mid-September, seventeen braconid wasps emerged. The same species of parasitoids were emerging from leaves collected in different towns.

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Normally, getting anyone to examine North American braconids is pretty much a lost cause, but it just so happened that these belonged to the subfamily Agathidinae, which is the speciality of Mike Sharkey at the University of Kentucky. So I sent them along to him, and he told me they belong to the genus Bassus, which he happens to be in the process of revising. They are either B. annulipes or (more likely) a closely related, undescribed species. When he is done with his revision, this species and the rest of the B. annulipes complex will be moved to a new genus, which may or may not be Therophilus.

Amid the flood of parasitoid wasps, a single adult moth emerged.

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I sent this moth and one of the inkberry moths to Jason Dombroskie at Cornell, and upon dissecting them he confirmed the assessment of some folks on BugGuide that both were Rhopobota dietziana (a species named for the same Dietz who described the weevil genus Orchestomerus, which was the subject of my first paper). And so the claim I made in my book about the winterberry miner turns out to be true. Winterberry was already a recorded host of R. dietziana, but the fact that the larvae are initially leafminers had not been documented before–on this softer-leaved host, the larvae eventually abandon their mines and feed in shelters created by crumpling or tying the leaves. Inkberry is a new host record for R. dietziana. Chances are pretty good that this moth is also responsible for the similar leaf mines I have seen on American holly (Ilex opaca) and mountain holly (I. mucronata), but someone will have to raise it from those hosts to be sure.

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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One Response to Leaf-mining Leafrollers

  1. Quite interesting! I will probably pay closer attention to mines etc next year.

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