Liebig (1998) quantified the impact on colonies when
applying OA solutions with concentrations greater than 5% and described significant
adult bee mortality, poor over-wintering ability, and impaired spring development.
A single autumn spray treatment using a 3.0% OA sugar water solution (1:1
by weight) and doses of 3-4 mL per comb side provided efficacies of 97.3 to 98.8%
(Charrière et al. 2004, Imdorf et al. 1995). These doses were tolerated well as none of
the experimental colonies lost their queen and adult bee mortality was not significantly
There are several accounts in the literature of
increased adult bee mortality as a result of OA application within hives (Charrière and
Imdorf 2002, Imdorf et al. 1998), suggesting that OA may not exhibit its lethal effect on
honey bees until more than 24 h after exposure.
I conclude that repeated applications of OA did not significantly reduce Varroa
mite populations in honey bee colonies when brood was present. My results confirm the
observations that OA is less effective when significant brood is present (Fuchs 1990,