Understanding the impacts of oxalic acid application methods on Apis mellifera and control of Varroa destructor

Varroa destructor is an ectoparasite of honey bees (Apis mellifera) and deteriorates colony health by feeding on immature bees and vectoring a suite of harmful viruses. Beekeepers work to manage V. destructor infestations by applying chemical treatments, including oxalic acid (OA). Oxalic acid is an organic acid that can be delivered to colonies through multiple methods, including strips, vaporization, and liquid dribble. While research has demonstrated OA efficacy against V. destructor, best practices for the delivery of OA through vaporization and dribble are undefined. Our aim was to improve OA administration by (1) assessing effective vaporization temperatures to reduce V. destructor infestations and (2) comparing novel and existing methods of OA application. To evaluate vaporization temperatures, we conducted a field trial with forty colonies divided amongst four treatment groups (no treatment, OA vaporized at 180°C, 230°C, 280°C). To compare existing OA applications with a novel method, we conducted a field trial with fifty-five colonies divided into 5 treatment groups: no treatment, positive control (amitraz), OA/sugar-solution dribble, OA vaporization, and OA/glycerin Ready-to-Use dribble. In both trials, V. destructor infestation levels were measured through alcohol washes before and after treatments and monitoring mite fall with sticky board traps. We assessed colony strength parameters before and after the course of treatments in both studies to observe any effects of treatments on colony health. The results of these field trials will aid in standardizing best practices for OA vaporization and exploring new treatment options for beekeepers.