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Photo#1181294
Unknown Solidago/Eurosta gall borer

Unknown Solidago/Eurosta gall borer
Hawkeye Wildlife Area, Johnson County, Iowa, USA
January 27, 2012
These Eurosta solidaginis galls, and others similar to them, have been collected by my students in fall-winter. In each case the galls have been bored into by what I assume is a lepidopteran larva, which then pupates inside the gall. By the time we collect them, they are empty, but we have found exuvia, silk and the substance top the far right in this photo (perhaps the result of a failed pupation?) In every case, the borer enters the mature gall from the underside at the juncture of the stem and the gall. Does anyone know who does this?

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Unknown Solidago/Eurosta gall borer Unknown Solidago/Eurosta gall borer Unknown Solidago/Eurosta gall borer Unknown Solidago/Eurosta gall borer

Moved
Moved from ID Request.

A closeup of the objects to the right would be nice...
but they sort of look like they could be leafcutter bee nest cells.

 
Gall Borer ID
I have posted some additional photos of the contents, though I am not sure they are helpful. Do you think this could be leafcutter bees? Would they make the borehole, or do they just use existing holes?

 
Maybe not
They look less like leafcutter bee nest cells than I thought. Leafcutter bees typically use preexisting cavities (though some may dig in soil), so even if these were their nests they probably aren't what made the holes. I've never seen holes like this--normally the only holes I see in these galls are the ones made by downy woodpeckers going after the fly larvae (or tiny holes made by emerging parasitoids).

Are the exuviae you found larval or pupal exuviae? Photos of them might help. The presence of silk does suggest a moth larva though. Was there frass inside, or just the objects you already photographed? Are those solid, the same consistency all the way through?

 
Gall Borer ID
Sadly, I do not have specimens of these anymore. I keep looking for them when I return to this site. I do research on turtles at the site in the summer. This summer we found one of the bored galls and tried to bring it back to the lab,but during a day of scrambling through the tallgrass, the stem was pulled from the bucket we had it in. Ido take students there in some years to do a gall lab. Problem is, we really reduce the number of galls when we take a sample of reasonable size, so I have not returned to that site to do the lab for several years. Maybe I will do it here in the next couple of months, but I expect we will find only non-living remains. The stuff in the photo seems to be a sort of crumbly solid - not frass, I don't think, but maybe some sort of sap or... ? Holes really are consistent in every gall I have found them in - enter from the bottom at the stem/gall junction, pretty consistent in size. I will post more info if I find more galls.

 
Galls with holes
Downy woodpeckers make similar holes and extract the larvae in the galls. Favored food source.

 
The holes made by downy woodpeckers...
have more beveled edges and are more irregularly shaped.

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