I investigated strategies for reducing Varroa mite populations ( Varroa destructor ) in honey bee colonies ( Apis mellifera ) using oxalic acid (OA). I examined the efficacy of OA in both broodless colonies and colonies that contain brood. My data indicate that OA is most effective at reducing Varroa populations when colonies are broodless because repeated applications of OA did not significantly reduce mite populations in colonies when brood was present. Next, I quantified the contact toxicity of OA to Varroa mites and their honey bee hosts in laboratory bioassays. The results indicate that OA has a low acute toxicity to honey bees and a high acute toxicity to mites. The toxicity data will help guide scientists in delivering lethal dosages of OA to the parasite and in protecting its host.
I also investigated how OA is distributed in honey bee colonies when applied using the trickle method. For this study, I constructed nine divided Langstroth hives using 3 different types of dividers that allowed trophallaxis, physical contact, or fumigation. I treated bees on one side of the divider and then monitored mite mortality on both the treated and untreated sides. Bee-to-bee contact was the primary route for OA distribution. Finally, I developed a protocol for using OA to eliminate mites from package bees. I made 97 packages of Varroa -infested adult bees. I sprayed an OA solution directly on the bees through the mesh screen of the package cages using a pressurized air brush. I quantified mite and bee mortality and estimated the optimum dosage of OA to apply to package bees for mite control without injuring bees. The application of 3 mL of a 2.8% OA sugar water solution per 1000 bees will allow beekeepers to safely reduce populations of Varroa mites from packages prior to installation. My research is significant because it offers beekeepers a safe, effective, and sustainable method for reducing Varroa populations.
