Combining an artificial break in the brood cycle with an oxalic acid treatment to reduce varroa mite (Varroa destructor) populations in Apis mellifera colonies

In the summer of 2007 we investigated combining an artificial break in brood rearing with an oxalic acid (OA) treatment to reduce varroa mite populations in honey bee colonies. The experiment consisted of four treatment groups, requeen plus OA, requeen only, OA only, and untreated colonies. Queens were caged in the requeened treatment groups five days prior to placing a sealed queen cell in the colonies which provided a period of 18-21 days without egg lying. The absences of brood resulted in the all mites becoming phoretic on adult bees. A 50 ml application of a 3.0% OA sugar water solution (sugar: water) (1:1) (w:w:w) was applied to the requeen plus OA, and OA only treatment groups. The OA solution was trickled from above the frames into the bee-ways. Post-treatment alcohol samples were taken four days after treatment. The requeen plus OA treatment group had .192 ± .046 mites per bee in the pre-treatment sample and dropped to .039 ± .046 mites per bee in the post-treatment sample. The requeened treatment groups exhibited a significant decrease in mite population versus the untreated colonies. However, there was not a significant different between the two requeen treatment groups. This indicates that brood being present is not the only factor affecting oxalic acid’s efficacy rates. The data indicates that combining late summer requeening with OA treatment significantly reduces mite populations compared to untreated colonies.