If the mite number exceeds those above it is ime to treat. Cultural methods for Varroa mite control include using drone comb or bottom screens to trap Varroa mites. Varroa mites prefer drone brood. Using a few frames of drone comb per colony draws mites into the cells which are then capped by the worker bees, trapping the mites within. The frames are removed and put into the freezer 24-48 hours to kill the mites.
Bottom screens are also an effective control method.
They are basically a wood-bound screen that is placed underneath the brood chamber. The mites fall through the screen onto the bottom board or ground. The mites are thus separated from the bees and eventually die. It should be stressed that these two treatments alone will not rid your colonies of all Varroa mites and should be used as a means to delay the economic threshold and the need for a chemical application. Hopefully in the future, genetic bee stocks resistant to Varroa mites will become more available to beekeepers.