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From goldenrod round galls - Eurosta solidaginis

From goldenrod round galls - Eurosta solidaginis
Horsham, Montgomery County, Pennsylvania, USA
March 10, 2009
Goldenrod round galls come in different sizes. Apparently the smaller ones get attacked by parasites more often than others; but the larger ones attract the hungry eye of chickadees in winter. So there are two opposite selective forces at work.
A goldenrod round gall has a rich fauna. In addition to several flies, some braconid wasps (subfamily Doryctinae) emerged from these galls, considerably smaller than the Eurosta flies, 2-3mm. Several females and one male, so far:
       A different one

I also found a mordellid beetle and larva

some Eulophids

and Eurytoma
E. gigantea larva E. gigantea E. gigantea

More on Goldenrod Gall Fauna

Images of this individual: tag all
Fly from goldenrod galls. - Eurosta solidaginis - female From goldenrod round galls - Eurosta solidaginis

Moved from Braconid Wasps.

Interesting observation
Is that from your own experience or have you read about it somewhere? I can think of a couple of possible explanations, but I wonder if you know what the real reason is.

References on info page
I got some of the info here and in other sites listed on the info page. Unfortunately the one published by the Minnesota State U. is not available right now. I wonder why.
In additon to these galls I have a couple of larger ones with the characteristic chickadee's damage if you are interested. I wasn't sure if it was right to submit them to Bugguide.

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