> an italian report at:
>
> http://www.eureka.it/4a/english.htm
>
> describes the use of castor oil ...
 
Here is that text (Cleaned up a bit):
 
                       NEWS ON VARROA FIGHT
 
After one year of experimentation we can tell that a varroacidal effect can
be obteined by the insertion of seed oil (the one for alimentary use) in
the hives.
 
Oil is surely known, in  the centuries, in the fight against the parasitic
mites of man (lice, crab-lice) and other domestic animals (ticks). Its
effect is based on suffocating, in fact, the varroa - which has a high
surface/volume ratio due to its flat form.  (Varroa) makes a great part of
it's oxygenation through its chitinous cover; if its pores are obstructed
from the oil, the varroa dies of suffocation.
 
For this it's necessary to grease the upper part of the frames and of the
top; bees, walking across the frames, dirty their legs, and trying to clean
themselves, spread the oil  all over their body.
 
We suggest to go on in this way: Take off the top, (knock) the bees
from it into the hive and paint (it) using 15cc of oil.  Remove the bees
from the frames by a little of smoke, and spray a trickle of oil (about 1
cc) by a sprayer on the upper  part of the wood sheet(topbar) of every
frame (it' s not necessary to take off (out) the frames).
 
Beware to not spray oil directly on bees. Beware to not spray oil between
frame and frame. Beware to not put oil on frame's sides. Luckily, because
of its density, in the sprayers the oil tends to discharge (as a) stream
and not vaporized.  That makes it easier.
 
This method of fight has many advantages:
1) It doesn' t injure to the image of  the honey  because it doesn' t
induce scare of eventual residues.
2) It can be used also in the "harvest-time" with out problems of
contamination of honey with noxious substances to man' s feeding.
3) It is easy to use and it doesn' t need a great effort of the beekeeper.
4) It can be used during all the normal visits to the hives.
 
But, as disadvantage, we can tell that, acting only on varroa that
parasite the adult bee (phoretic mites) and not on those that parasitize
the eggs (larvae), the method has a limited effect. To obtain a result you
have to repeat at least 4 treatments in a month (one a week).
 
Anyway the oil is also a good way to introduce other active substances (of
natural origin) in the hive, i.e.: thyimol and menthol, that split up
(dissolve) in it, so that you can obtain a synergic effect and longer
during the time, with a great result.
 
Translation by: Francesca Quadrini