For those of you wishing to know a bit more about butyric acid as a bee
repellent:

I first learned about butyric acid when I was a 16-year old, working in a
restaurant, and as a prank, a buddy rubbed a large handful of soft butter
into my hair.  Even after shampooing, over the next couple of days some of
the remaining milkfat in my hair naturally degraded into butyric acid (from
the Latin word for butter--butyrum).  Butyric acid is the chemical that
gives vomit its distinctive aroma, and the decomposing butter residues
certainly gave my hair an embarrassingly strong scent to that effect.

Since that time, I've used butyric acid in entomology labs as a fly
attractant, and on one occasion for a stinky prank.  As a beekeeper, I used
it in the form of the original Bee Go (don't plan on eating at a restaurant
after using straight butyric acid in the beeyard).  Any number of
beekeepers spilled a bottle of the old Bee Go into their trucks, and were
banned from parking near their growers market.

Butyric bee repellents were improved by using instead of butyric acid, its
dehydration product butyric anhydride (created by removing a water molecule
to join two 4-carbon acid molecules into an 8-carbon anhydride (meaning
"without water").  Some formulations add a cherry scent to mask the odor.

An advantage of the anhydride is that it has an extremely low vapor
pressure--meaning that it will not evaporate (outgas) very strongly. It's
vapor pressure at 25C is only 0.3 mm Hg, compared to the vapor pressure of
water at that temp of 17.5 mm Hg, indicating that it would evaporate at an
extremely low rate.

However, as the anhydride reacts with moisture from the air, it splits back
into two molecules of butyric acid, each with a vapor pressure of 1.65 mm
Hg--suggesting an evaporation rate of better than 5x that of the
anhydride.  This water-dependent reaction would tend to moderate the
release the vapors of butyric acid from the fume board.

It doesn't take much for it to have a repellent effect, and as far as human
safety, it is a naturally-occurring molecule in your stomach contents
(remember the odor in vomit), and is strongly apparent in smelly cheeses.

-- 
Randy Oliver
Grass Valley, CA
www.ScientificBeekeeping.com

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