Abstract For over 40 years, the mite Varroa destructor has devastated colonies of the honey bee Apis mellifera . Without treatment, colonies typically die within 1–3 years. Recently lithium chloride (LiCl) has been found to be an effective varroacide at a concentration of 25 mM when mixed into the food of the bees, but unfortunately this treatment harms the honey bee brood. Based on an experiment with the clawed frog Xenopus laevis , where monosodium glutamate (MSG) had a protective effect, we investigated if adding MSG into the treatment can reduce the impact of LiCl. We tested different concentrations of MSG in the LiCl syrup and fed it to caged bees as well as free-flying colonies. First, we investigated the survival rate of adult honey bees in a cage trial while feeding 25 mM LiCl syrup with three different concentrations of MSG (0.4 g/L, 0.8 g/L, and 1.2 g/L MSG) and two control syrups (plain syrup and 25 mM LiCl) over a period of 27 days. The treatment group with LiCl + 0.4 g/L MSG had a significantly higher survival rate while the treatment with LiCl + 0.8 g/L MSG and the positive control led to the lowest survival rate. We proceeded to a field trial, observing the impact of two MSG concentrations (0.4 g/L and 0.8 g/L) and a LiCl-only control on brood development in bee colonies. Regular assessments revealed no significant differences in brood removal rates between the treatments, though absolute removal rates were higher with the addition of glutamate. In summary, while adult bees tolerate glutamate in syrup, it does not alleviate LiCl’s harm to brood and may increase brood removal.
Schneider et al. (Thu,) studied this question.