I know a little bit about that subject.  :)

> common commercial scented butyric acid repellent

Bee kills from butyric anhydride products are far more common than you might
suspect.

If you look up  butyric anhydride, you'll find warnings about "respiratory
depression", and "circulatory shock".  The first means that you can't get
any oxygen from air, the second means that your cells aren't getting any
oxygen.

The bees at issue suffocated from too much chemical and/or too hot a day.
The impact of hot humid weather on the oxidation rate of the butyric
anhydride is decidedly non-linear.    There have also been a small number of
beekeepers who have had close calls after getting a good whiff of butyric
anhydride, so the effect is cross-species.

The chemical you are using is not "butyric acid", despite the deliberate
mislabeling.  It is pure butyric anhydride.  It's a rather nasty haz-mat
corrosive chemical that should be handled with gloves, mask, and a chemical
fume hood that meets various specs for volume of air removed per minute.

Butyric acid is one of the byproducts that results after butyric anhydride
reacts with oxygen in the air (or acts as a corrosive when reacting with the
oxygen in water).  Not all the butyric anhydride reacts, of course.

I'm surprised that anyone still uses any of the butyric anhydride products,
as the EPA revoked the "exemption for the requirement for a tolerance" in
food back in 1998:

http://web.archive.org/web/20030429143659/http://www.epa.gov/pesticides/tole
rance/tolrev.htm
http://tinyurl.com/gvugneh

If there is no EPA tolerance for the chemical in food, and the FDA does not
list it as "Generally Recognized As Safe" (GRAS) in food, then one must not
use the chemical in close contact with food, or one has "adulterated" the
food, and adulterated food may not be sold.  Attempting to remove the
adulteration gets one in even more trouble.

Without a tolerance or exemption, food that comes in contact with this
pesticide is considered unsafe and therefore "adulterated" under section
402(a) of the FFDCA and hence may not legally be moved in interstate
commerce (21 USC 331[a] and 342[a]). 

But sales continue, as the EPA and the states are more likely to approve a
fracking lease next to your beeyard than they are to enforce any of the
pesticide regulations to actually protect bees.  Beekeeping is simply too
small a market segment for regulators to notice.

To make matters even worse, there are now several knock-off non-butyric
anhydride products for fume boards which are falsely labeled "natural" in an
attempt to compete with the single more expensive, but truly natural
product.  They are synthetic, not at all natural.  Yes, they are also
Haz-Mat.

It is a self-correcting problem in a macabre way, as one inhales
carcinogenic fumes when handling these synthetic chemicals, and I doubt that
any of them have taken enough chemistry to realize that they need very very
expensive masks and such to protect themselves from long-term damage to
their respiratory system and cancers of the throat, lungs, etc.   There's no
risk to the beekeeper handling the highly-diluted chemicals "as sold", the
respiratory damage is only suffered by the knock-off artist who tries to
make an easy buck.  It is sad, as the damage would be undetectable without a
pulmonary function test, but would be significant after a limited exposures
period.

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