Bill Truesdell asks about a concoction of different oils of essence (a more correct name for essential oils). > 100 gram bottle of thymol, Add 1/2 ounce of menthol and 1/2 ounce of > champhor... > This treatment was developed by Nick Calderone when he worked at > Beltsville.... Nick's work was initially very promising, his concoction appeared highly effective and there was quite a stir in the beekeeping community. There were others doing similar work (James Armine in West Virginia for one) on oils of essence. I believe Jim's work is available online, although I don't recall the url, but it's in the BEE-L archives. Calderone was doing his work right around the time he succeeded Roger Morse at Cornell. Subsequent experiments had less promising results. Conclusions were that the treatment can be highly effective, sometimes, but not reliably. This seems to be a common theme in the varroa saga. A treatment looks effective, but doesn't stand up to scrutiny. It's a long list including oils of essence, mineral oil, screened bottom boards, smoker fuels (many of which have been touted - cedar shavings, stag horn sumac, grapefruit leaves, ...). Most of these treatments have been discussed and disseminated on BEE-L, have been quickly picked up by the beekeeping community and have subsequently not stood up to field laboratory studies. The rapid dissemination of "shaky science" has been an oft heard criticism of BEE-L and internet lists in general, which is why you have to be cautious of what you read and try. And this is not to say that none of the treatments discussed here or mentioned above are useless. Many are included in the arsenal of IPM. The problem with these treatments is that they don't achieve the levels of control that did Apistan or does for the time being (resistance is already showing up in where else? Italy!) Coumophos. That the above mentioned treatments do not achieve 99% knock down of varroa has had them looked upon with lesser favor from the commercial ranks, where time of treatment (labor costs) is a big part of the considerations. However, ever 99% knock down is being reexamined as a goal, as it's that remaining 1% that breeds the resistance to the treatment du jour. The latest aim is to reach the "economic threshold", defined as the level of varroa a hive (or yard) can tolerate without causing economic loss. I understand the concept, but find it laughable. With the dynamics of varroa populations, the economic threshold this week can grow exponentially to crash level and severe economic losses in a very short time. But anything that can knock back (not eliminate) the varroa population is a good thing. A round of drone trapping is a set back in an exponential curve. A less than 99% knock down achieved by an oils of essence treatment is a set back in an exponential curve. Mesh bottoms alone, still show an exponential curve, although the rate of increase is not as dramatic. Combinations of the above treatments give continual set backs in the exponential curves, and can keep varroa populations below the "economic threshold" if the threshold in your operation does not include the labor costs to employ the method(s) of control. Aaron Morris - thinking like a mathematician!