Testing efficacy, toxicity, and residue of a stabilized oxalis acid formulation for control of Varroa mites

One of the significant threats to the health of western honey bees is the parasitic mite Varroa destructor. Chemical treatment abuse and poor management have resulted in widespread resistance in Varroa populations. However, one suggestion for better chemical Varroa control is to enhance the formulation and use of current miticides, mainly when brood is present. Unlike many other miticides, oxalic acid (OA) has maintained its efficacy and can be applied in vapor or liquid form to control mites. However, each method requires repeated treatments while brood is present, which may be inconsistent and labor-intensive. In addition, OA is limited in warm areas with a lengthy brood-rearing season because these mites are protected in capped brood during these seasons, highlighting the need for an improved formulation to delay/extend its release. This research investigates the potential effects of a stabilized OA product, VarroxSan, hypothesized to have a chemical property that extends the release of OA for about 56 days in the colony, reducing the labor of reapplication. Thirty-two healthy colonies were divided into four treatment groups with the same average Varroa infestation level. VarroxSan was tested in two doses and compared with the industry standard dose of Apivar treatment and a no-treatment control for efficacy, toxicity, and residue. After 56 days, we found that VarroxSan performed as well as Apivar, with the added advantage of lasting longer, reducing the frequency of apiary visits. Successful registration of this product would create a long-lasting, labor-saving, alternative, valuable IPM tool at a critical time.