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Photo#530654
Galls on oak - Andricus quercuscalifornicus

Galls on oak - Andricus quercuscalifornicus
Pleasant Hill, Contra Costa County, California, USA
June 16, 2011
Several oaks next to the Iron Horse Trail had galls like these, either singly or paired. The larger gall was 2.3 cm across, and a beetle was found on it:


Moved
Moved from Gall Wasps.

about the beetle....
Just read the comments with the beetle image. So the gall had exit holes -- yes, old gall.

I'm pretty sure Gary is right, the beetle is Ozognathus cornutus. They're known to live/develop in these galls. Most of the Ozognathus cornutus I've seen did not seem to be associated with galls, but this year I finally reared some from Andricus quercuscalifornicus galls.

 
About the galls
The gall on the right has a big hole that's partly visible in the photo. Both galls were almost white, as were all the ones I saw.

Thanks for the IDs. I'll move everything.

Andricus quercuscalifornicus
The gall is caused by Andricus quercuscalifornicus. The galls are green or red when fresh, then turn tan/brown with age. These may be galls from last year. Did they have exit holes? If so, they are definitely from last year (or a previous year).

The tree is most likely valley oak (Q. lobata) but there's a small chance it could be Oregon white oak like you say. Q. garryana is not as common in Contra Costa county as Q. lobata.

 
Valley oak
Revisited the same trail today. An informational sign on another part of it, about a mile away and in Walnut Creek, listed valley oak as a common species along that trail.

Beneath one large oak were numerous light brown galls of this kind with exit holes. I opened one and found a white larva inside, about 5 mm long, which I didn't photograph because it was too active for anything but a blurry shot. That might be the beetle larva.

Moved
Moved from Unidentified Galls.
I'm ignorant of California oaks, and I don't know which species this might be, but if you can figure it out I'm sure that will be helpful. Joyce Gross may recognize the galls anyway... in the East the "oak apples" like this are all caused by Amphibolips species, but I think that may not be the case in California.

 
Oak spp.
From a little Googling, using only leaf shape, the most likely oak species are valley oak (Q. lobata) and Oregon white oak (Q. garryana). I don't have acorns to help with ID.

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