Re: Thymol toxicity. 

I have always been interested in Thymol as a varroa control, and have tried to get discussions going on it here on numerous occasions. The apparent discrepancy in reports may in fact be tied to differences in climate. For example, post harvest treatments with formic acid are useless in our climate, since the honey flow may go to the end of September and may be followed by daytime temperatures in the 50 F (10 C) range. However, this temperature may be optimal for Thymol products.

> Chiesa (1991) was able to control V. jacobsoni in honey bee colonies with thymol without noticeable damage to the colonies at temperatures ranging from 5 to 9 C (41-48 F). However, Gal et al. (1992) found thymol applications deleterious to bees when temperatures reached 27-28 C (80-82 F). Overlap in the LC50 confidence limits for bee and mite mortality found in this study supports the findings of Gal and his colleagues that thymol is too toxic to bees for use at high temperatures.  --Toxicity of Seven Monoterpenoids. Marion D. Ellis. J. Econ. Entomol. 90(5)

This 1997 study looked at citral, thymol, carvacrol, a-terpineol, pulegone, d-limonene, and menthol.

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