In the states, a prophylactic treatment for tracheal mites is to keep
a constant presence of vegetable oil in the hive via grease patties.  It
was discovered that the continued presence of grease patties impeded
tracheal mites' ability to recognize an acceptable host when they find
it, thereby increasing the probability that the mites meet a natural
demise before infesting a hive.  Grease patties is NOT a treatment for
infested hives, it's a management technique to keep your hives from
becomming infested.
 
This has been covered extensively before on this list (search the
archives) or surf to:
http://apicultureNE.cas.psu.edu/
and follow the path: "Extension Publications" and "Grease Patties"
 
Aaron Morris - I think, therefore I bee!