Many of us who have used formic acid have SEEN it cause harmful effects on the brood and the queens. This is no myth. 

QUOTED MATERIAL:

Formic acid had immediate and significant effects
on brood survival during the first week of treatment
(Table 4). The rapid evaporation rate seen in the first
week of treatment clearly reduced brood survival.

The significant reduction in brood presence in the first
week of formic acid treatment accurately reflected the
immediate toxic effects of high levels of vapors. 

Additionally, no eggs or brood were found in two formic
acid-treated colonies a week before 26 March, and no
eggs or brood were found in one formic acid-treated
colony the week before 9 April. In the colony referred
to of 9 April, supercedure was apparent. These data all
demonstrate the toxic effects of the formic acid treatment
on brood development.

Formic Acid Treatment for Control of Varroa destructor
Under Southern United States Conditions
PATTI J. ELZEN, DAVID WESTERVELT, AND RAYMOND LUCAS
JOURNAL OF ECONOMIC ENTOMOLOGY Vol. 97, no. 5

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