The efficacy and tolerability of Api-Bioxal® as a winter varroacide in a cool temperate climate | Eficaciay tolerancia de Api-Bioxal® como varroacida invernal en un clima templado frío

This two-year study aimed to assess the efficacy and tolerability of the oxalic acid product Api-Bioxal® as a winter treatment administered using the trickling and vaporizer methods at the dosage rate recommended by the manufacturers (Trial 1) and at the lower dosage recommended by The European Group for Integrated Varroa Control for cool temperate climates such as Ireland (Trial 2). Trial 1: In August 2011, 45 colonies were standardized based on brood area and blocked into 2 treatment groups (n = 15) and a control group using natural mite-fall pre-treatment. Three weeks post-treatment a control treatment (CheckMite⁺) was administered to the test colonies and the percent efficacy of Api-Bioxal® was calculated. Invasion pressure was monitored by treating the control colonies continuously with CheckMite⁺. Tolerability was assessed by monitoring adult bee mortality post-treatment and spring build-up was assessed on brood area. The mean (± s.e.) percent efficacy for the trickling method (81.5 ± 3.5%) was significantly lower than for the vaporizer (95.2 ± 1.6%) and control (97.7 ± 1.0%) groups. Bee mortality post-treatment was significantly higher in the trickling group but Api-Bioxal® treatment had no negative impact on spring build-up irrespective of the application method. This high bee mortality and relatively low efficacy led to Trial 2. Trial 2: In August 2012, 72 colonies were standardized using brood area and divided into 5 treatment groups (n = 12) plus a control group. The application methods and dosage rates recommended by the manufacturers (6.0% trickling method in a 1:1 sugar/water syrup and 2.3-g vaporizer method) were again assessed in addition to a lower dosage of 4.5% in 1:1 sugar/water using the trickling method and 1.3 g for vaporizer method. The control colonies were untreated. The mean percent efficacy calculated for the five treatment groups exceeded 90% and were all significantly higher than the 8.57% efficacy estimated for the control group. Bee mortality was again significantly higher in the colonies treated using the trickling method at the 6.0% concentration and significantly decreased when the dosage concentration was reduced to 4.5%. Api-Bioxal® applied using the vaporizer method, irrespective of the quantity administered, was well tolerated by the colonies and bee mortality was similar to the natural mortality observed in the control group. We conclude that in a cool temperate climate, Api-Bioxal® is an effective varroacide when administered as a single winter treatment under broodless conditions using both the trickling and vaporizer methods. Colonies tolerated the product better at the reduced dosage rate of 4.5% using trickling method or 1.3 g using the vaporizer method without compromising the efficacy of the treatment.