Great post Peter, I found it quite interesting. I contacted Marla about the propolis envelope and got a quick reply back.  If brood boxes simply have a rough finish like unplanned wood the bees will make a propolis envelope. 

Peter maybe you have easy access to her paper on propolis and honeybee immune system I think she published recently. I know she has grad students working on various research projects concerning propolis and its benefits to humans and honeybees. 

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