This question came up during today's monthly bee meeting concerning Thymol in bee hives:
Thymol, an essential oil going by the brand names of Apigard, Thymovar, ApiLifeVar is NOT to be used when honey supers are on the hive. Apigard is placed on top of frames for 2 treatments, 2 weeks apart. Thymovar and ApiLifeVar are placed on top of frames for 2-3 treatments, at 7-10 day internals. This group of miticides are temperature dependent and do not work well in cooler temperatures.
Also for a review:
The organic acids includes formic acid (MAS strips, Formic Pro), oxalic acid, and the hops based organic acids (HopGuard II and HopGuard III). They can be used when honey supers are on. The challenge in using HopGuard is that brood should not be present during use. There is caution with formic acid due to potential damage to brood and queen fertility. Specific restrictions do apply when harvesting honey after HopGuard treatments. Formic acid should not be used in extremely warm temperatures. See insert.
Synthetic chemicals include Amitraz (Apivar), Fluvalinate (Apistan) and Coumaphos (CheckMite), and are also known as "hard" chemicals. These treatments should NOT be used when honey supers are on. Treatment durations last several weeks. Once strips are removed, there is an additional holding period of approximately 14 days before honey supers are put on. CheckMite should never be used in queen rearing colonies. See inserts for details. Disadvantages to this class of miticides is that mite resistance has already been reported and traces of chemicals can commonly be found in exposed comb and wax. Residues in honey has to be avoided as a recent report issued from the EU showed that if any honey produced in Europe is found to contain chemical residues, amitraz is one of the most commonly found residue. For this reason, amitraz is banned in Europe for use as a plant protectant. It does allow a severely restrictive use in veterinary medical products. Also, if foraging bees encounter environmental pesticides and bring these back to their hives, there could be a toxic synergistic effect between environmental pesticides and the applied chemical miticides within the hive environment causing greater damage.
As with all products, follow insert guidelines.