Determining the dose of oxalic acid applied via vaporization needed for the control of the honey bee (Apis mellifera) pest Varroa destructor

Abstract

Oxalic acid (OA) is a natural compound that has been used to control the honey bee (Apis mellifera) pest Varroa destructor. One method of OA application gaining popularity among beekeepers in the US involves vaporizing OA crystals with heat inside a closed hive. Herein, we tested different doses of OA applied via vaporization to determine the most effective amount of OA needed to reduce V. destructor populations below that of the negative controls. Forty experimental colonies were assigned to one of four treatment groups, with ten colonies composing each group. The four treatments were: (1) 1 g OA, (2) 2 g OA, (3) 4 g OA and (4) no OA (negative control). The OA was applied via vaporization once per week for three weeks. V. destructor infestation rate and colony strength assessments were estimated before, during, and after treatment applications. Colonies in the 4 g OA treatment group had significantly lower infestation rates than did those in the untreated control and 1 g OA treatment groups, but not those in the 2 g OA treatment group. The infestation rate of colonies treated three times with 1 g OA, which is the current legal limit for OA vaporization in the US, was not significantly different from that of colonies in the negative control or 2 g OA treatment groups. Colonies receiving the highest dose of OA were generally healthier than those treated at lower OA doses. Our results may lead to improved efficacy of OA vaporization, thus aiding beekeepers in their efforts to control V. destructor.