Interlopers

I’ve been making sporadic progress in sorting through my backlog of photos, and I’m now exactly seven months behind. April 13 saw the conclusion of a story that began with my collecting this scrub oak (Quercus ilicifolia) leaf in early October of 2018:

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The brown, wrinkled patch is a leaf mine of a moth in the genus Cameraria (Gracillariidae), but which of the 30 oak-feeding Cameraria species is it? I periodically collect oak Cameraria mines to see if I can figure out ways to distinguish the different species.

I removed this leaf from winter refrigeration on March 1, and on March 10 I discovered this little caterpillar spinning a cocoon in the bottom of the rearing vial:

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This was clearly not a Cameraria larva, which would be flattened and legless and would pupate inside the leaf, from which the adult would eventually emerge. It was a larva of one of the bigger micro-moths, probably something in the superfamily Gelechioidea (or maybe a tortricid). It had evidently been inside the mine when I collected the leaf and had spent the winter there.

The next day it was still working on its cocoon; in the photo below it’s lying on its back and adding silk to the ceiling:

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On March 20 the larva abandoned its cocoon and disappeared into the crumpled-up piece of toilet paper I had stuffed into the vial for humidity control. At this point I knew my chances of learning the identity of this interloper were not good; a happy, healthy caterpillar does not leave its carefully constructed cocoon behind. On April 13 this ichneumon wasp emerged from a cocoon spun next to the caterpillar’s remains inside the wad of paper.

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It turns out I was a bit hasty in saying at the beginning of this post that April 13 was the end of this story. Nearly two months later, on June 10, the adult Cameraria emerged from the same mine:

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I tried running it through the key I made here to the known eastern oak-feeding Cameraria species, and I think C. bethunella may be the best match. Unfortunately this is a species complex that needs more work, and I’ve reared much smaller moths with a similar wing pattern from completely different mines. So no name for this moth just yet…

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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5 Responses to Interlopers

  1. Anonymous says:

    This reminds me of the dark nursery rhyme:
    There was an old lady, who swallowed a fly…

    There was a scrub quercus, that hosted a moth etc.

  2. murwat says:

    I really enjoy your blog, your curious mind, and your determination to follow through and learn what’s going on. if possible, it would help me understand this world of leaf miners better if you gave us some idea of size. Are these larvae, wasps and moths just a few millimeters in length? In any case, keep wondering, paying attention and sharing what you find! Thanks.

    • Thanks for the comment. In general, yes, anything I’m rearing from leaf mines is just a few mm long. The mystery caterpillar and ichneumon wasp were each about 6 mm, and the adult Cameraria was about 4 mm.

  3. Linda G. says:

    So to clarify, the leaf mine originally contained both larva: the mystery larva and the Cameraria, right? The “mature” mystery larva was spinning its cocoon in the rearing vial; did you see an exit hole in the leaf mine? Just curious. Fascinating story and incredible photos. Thanks!

    • Yes, apparently both larvae were feeding together in the mine. I didn’t find any external feeding sign from the mystery larva (normally when an unexpected caterpillar shows up in a leaf, there is lots of frass and evident external leaf damage to go along with it). As for the exit hole–I don’t specifically remember, but I’m sorting through my pressed leaves right now, and I’ll double-check when I get to this one.

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