Investigation of the acaricidal efficacy, tolerance and residue levels of thymol-containing gelatin-based hydrogel developed for varroosis control

The aim of this study was to investigate the acaricidal efficacy, tolerability of the target species and residue levels of a thymol-containing gelatin-based hydrogel developed as a controlled release system for varroosis control. The study was carried out on naturally infested honey bee colonies and compared with those of the negative control and positive control groups. The acaricidal efficacy (%) of the negative control, positive control and hydrogel was 21.93 ± 2.87, 81.09 ± 2.30 and 70.32 ± 2.05, respectively. For the tolerability controls, the average number of dead bees per colony was determined to be 60.80 ± 8.01, 297.40 ± 21.4 and 86.80 ± 6.94 for the negative control, positive control and hydrogel, respectively. The average thymol residues in honey were measured as 0.030 ± 0.022 mg/kg, 5.498 ± 3.346 mg/kg and 0.168 ± 0.110 mg/kg for the negative control, positive control and hydrogel, respectively. The average thymol concentrations in the beeswax were 0.074 ± 0.047 mg/kg, 1.667 ± 0.855 mg/kg, and 0.476 ± 0.278 mg/kg for the negative control, positive control, and hydrogel, respectively. The controlled release system developed in this study was found to prevent the transport of thymol out of the colony, due to its structure which is well tolerated by bees. Consequently, a single application can achieve longer infestation control. Furthermore, the lack of intervention by bees in the system has ensured that bee mortality due to contact toxicity and residue levels in honey and beeswax are low. In addition to these advantages of the system, further development is required to increase the acaricide efficacy in order to make it an ideal alternative to existing varroacidal veterinary medicinal products.