Essential oils, in regards to mite control, have two apparent modes of operation, primarily, direct toxicity. In the case of varroa mites, once a mite comes in to direct contact with an essential oil such as wintergreen or tea tree oil mixed into a grease patty they are usually killed within a few minutes. This however, requires that the infected bee actually contact the grease patty. Due to this contact requirement, direct toxicity cannot eliminate mites, only aid in the control of mite levels. Secondly, it appears mite reproduction can be impaired when bees are fed a syrup containing essential oils. Essential oils are passed from feeding bees to other bees and larva through trophallaxis. Essential oils thereby pass to the brood and poison any female Varroa that attempt to parasitically feed on the larva.
Similarly, essential oils appear to have an impact on the breeding and control of tracheal mites, however the effects of tracheal mites are difficult to observe and the mechanism that causes the control is in debate. It appears that the best therapy, in regards to tracheal mites and essential oils, is the usage of grease patties.
It is recommended that that grease patties containing essential oils, and other medicaments as desired, are kept on the hives throughout the winter and any season when honey collection for human consumption is not taking place. Grease patties not containing any essential oils or medication should be kept on hives throughout the rest of the year. During times of the year that temperatures allow for flight, and honey is not to being collected for human consumption, colonies should be treated with syrup containing essential oils.