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Photo#896196
Stem Gall on Leafcup

Stem Gall on Leafcup
100 Acre Wood, Winneshiek County, Iowa, USA
October 5, 2011
October 3, 2011: collected stem gall on Leafcup, Polymnia canadensis
May 13, 2012: gall is covered in fungus. One nearly dead wasp and a very dead wasp still in the decaying gall.
Naturally, this is the only gall I've seen on Leafcup. I keep looking.

Images of this individual: tag all
Stem Gall on Leafcup Stem Gall on Leafcup

Moved
Moved from Unidentified Galls.

Polymnia associates
Basically, anything you rear from Polymnia canadensis will likely be new to science. Felt, Weld, and Gagne list no Polymnia galls. There is one leafminer, Sumitrosis inaequalis, reported from Polymnia sp., but it's conceivable that that record actually refers to Smallanthus uvedalius (I'm not sure how recent that name change was).

My first guess for this gall would be a Neolasioptera (Cecidomyiidae), but as I commented on the parasitoid photo, a stem swelling in a composite could also be Cynipidae, Tephritidae, Gelechiidae, Tortricidae...

The only Polymnia associate listed in the HOSTS database is Papaipema polymniae (Noctuidae). Papaipema spp. are stem borers, but I don't know of any that cause galls.

 
Actually...
the original description of Papaipema polymniae (see page 123) says: "While the stem has a slight hollow core and though the walls are heavy, feeding continues at one point long enough for the plant to produce a noticeable swelling that gives ready intimation of a contained host. No parasites were encountered, but a heavy mortality resulted from fungus infection, probably the same as occurs with speciosissima, as the coloration and effects seem identical."

...Oh, but I see now that the first paragraph of that paper names the host as Polymnia uvedalia, i.e. Smallanthus, even though the HOSTS database just says Polymnia. Also, note that the swelling caused by a Papaipema larva would be associated with a long gallery in the stem, and wouldn't cause a rounded gall like this in one spot. Plus, the torymid parasitoid suggests a midge or wasp host, I think.

Well, that was a nice little diversion. Now, back to making leaf mine keys. I might finish the aster family today...

 
But now
you've given me a second reason to pay closer attention to these plants.
Thanks, as I had no idea as to Papaipema

Moved
Moved from ID Request. Charley Eiseman will find it more readily on this page.

 
Very good.
And thanks!

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