I have never heard of menthol having any reported effect on varroa.

A friend mentioned to me yesterday that she had read in the ABJ or Bee
Culture that menthol used to treat for tracheal had been noticed by someone
to have caused at least some live varroa to drop off the bees onto the hive
floor.  Thus -- IF this is true -- menthol potentially should have some
beneficial effect on varroa levels where open mesh floors are in use.

Since many BEE-L members use the screened bottom boards and some use
menthol, can anyone confirm this and, if so, comment on the degree of mite
drop?  We have started to use menthol in Blue Shop Towels, and wonder if
there is a side-effect on the varroa.

NOTE:  I am NOT saying this is true, and I do not want to start a mindless
rumour that menthol works on varroa.

I'm just asking.

allen
http://www.internode.net/HoneyBee/Diary/