In brief, "absolutely nothing".

While I'm sure Paul Stamets is sure to be a fungi to hang out with, I can
state from excruciatingly expensive personal experience that the claims of
Kanga (USDA) about the efficacy of Metarhizium anisopliae as a varroa
control were not able to be replicated by anyone, including Kanga himself.
There was also another soil bacteria named " Hirsutella thompsonii Fisher"
(no relation, its spelled differently), that initially seemed equally
promising, but did not perform as hoped on actual varroa.  

In 2006, the National Honey Board funded Rosalind James of USDA to make one
last try, just to verify that there wasn't some strain of Metarhizium that
might be of some value to beekeepers.  

I provided far more detail on this way back in 2008.  (Love that archives
search tool):
http://community.lsoft.com/scripts/wa-LSOFTDONATIONS.exe?A2=BEE-L;e0e7fe98.0
808B
http://tinyurl.com/lsyd9b3

And note that when one watches the video of Mr. Stamets claims about bees,
one sees other videos by Mr. Stamets were also on YouTube, with titles like
"Paul Stamets - Mushroom Science NO Trace of Cancer", "Paul Stamets - The
Future is Fungi [how to save the planet]", "Paul Stamets - Solutions from
the Underground: How Mushrooms Can Help Save the World", and so on.
There's also "fungi.com", where, no surprise, you can purchase not only
various potions and lotions, but you can get into the pyramid scheme of
"growing mushrooms" by buying all the "supplies" you need from him.

I simply don't have mushroom in my day for salesmen like this one. What he
proposes in regard to bees has already been completely debunked multiple
times.
The claims are thereby more implausible than those made about "Bulletproof
Coffee".

And what were his bees gathering from the mushrooms?  
Moisture!  Fungi get and stay very damp from the dew well into late morning,
check for yourself.

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