Thank you for confirming that I'm not crazy (at least on this point!). While trying to find out more, I came across this bit of info on use of essential oils for bees from (link suppressed as I am a newcomer).
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Using essential oils to kill both kinds of mites has been researched.
One of the problems with using essential oils is that many of the
compounds are toxic to honey bees as well as mites. Several herbal
extracts and essential oils have been tested. For the most current
information on using essential oils to control varroa mite, visit West
Virginia University's Web site, "Mite Control in Honeybees With
Essential Oils".
One study tested thymol-based products in Texas, Virginia, and
Minnesota. (Sanford, 1997) There were good results in Texas and
Virginia, but less mite mortality in Minnesota. One reason given for
this difference is that higher temperatures in the southern states
helped the thymol to diffuse into the colony. Another variable that may
have affected the study was the number of hive bodies — in Minnesota,
three brood chambers were used, while in Texas only one brood chamber
was used. The most effective blend in the study was thymol and
citronella.
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Steve