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Numerous studies have investigated using oxalic acid (OA) to control Varroa mites in honey bee colonies. In contrast, techniques for treating package bees with OA have not been investigated. The goal of this study was to develop a protocol for using OA to reduce mite infestation in package bees. We made 97 mini packages of Varroa-infested adult bees. Each package contained 1,613 ± 18 bees and 92 ± 3 mites, and represented an experimental unit. We prepared a 2.8% solution of OA by mixing 35 g OA with 1 l of sugar water (sugar: water = 1:1; w:w). Eight treatments were assigned to the packages based on previous laboratory bioassays that characterized the acute contact toxicity of OA to mites and bees. We administered the treatments by spraying the OA solution directly on the bees through the mesh screen cage using a pressurized air brush and quantified mite and bee mortality over a 10-day period. Our results support applying an optimum volume of 3.0 ml of a 2.8% OA solution per 1,000 bees to packages for effective mite control with minimal adult bee mortality. The outcome of our research provides beekeepers and package bee shippers guidance for using OA to reduce mite populations in package bees.

-Nine divided hives were constructed to study the distribution of oxalic acid (OA). Experimental colonies were split into two equal, queenright sections with one of three divider types. The first divider allowed trophallaxis to occur between adult bees on each side, but did not allow bee-to-bee contact. The second divider did not allow trophallaxis or bee-to-bee contact. The third divider allowed both bee-to-bee contact and trophallaxis between the two sides. All three dividers allowed gas exchange of volatile materials. The objective was to investigate factors that contribute to the distribution of OA in a hive by monitoring Varroa destructor mortality. Forty mL of a 3.5% OA sugar water solution was trickled on one side of the divider. Sticky boards were used to quantify mite fall before, during, and after OA treatment on both treated and untreated sides. Trophallactic interactions and fumigation did not significantly influence the distribution of OA. Bee-to-bee contact was the primary route for OA distribution.Varroa destructor / Apis mellifera / oxalic acid / mode of action / distribution

Laboratory bioassays were performed to characterize the acute contact toxicity of oxalic acid (OA) to Varroa destructor (Anderson & Trueman) and their honey bee hosts (Apis mellifera L.). SpeciÞcally, glass-vial residual bioassays were conducted to determine the lethal concentration of OA for V. destructor, and topical applications of OA in acetone were conducted to determine the lethal dose for honey bees. 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 optimum dosages of OA to the parasite and its host, and will be useful in making treatment recommendations. The data will also facilitate future comparisons of toxicity if mite resistance to OA becomes evident.