Liquid and solid matrix formic acid treatment comparison against Varroa mites in honey bee colonies

Beekeepers use organic acids to control the invasive parasitic mite Varroa destructor (Varroa mite) in honey bee colonies (Apis mellifera), as an alternative to synthetic acaricides, to which Varroa mites can develop resistance. Here, we tested the efficacy of two formic acid treatments for Varroa mite control: a solid matrix product (Formic Pro; n = 10 colonies) and a liquid product (Formivar 60; n = 10 colonies), relative to control colonies that were not treated with formic acid (n = 10). Both formic acid treatments killed >95% of the mites, however, the use of formic acid also resulted in 1.6 times more brood loss and 30% queen loss, relative to control colonies. Although the solid application was perceived as being more practical to use for treating against Varroa mites, both the solid and liquid application methods were equally effective and had similar negative side effects on honey bee colonies.