Effects of European foulbrood treatment regime on oxytetracycline levels in honey extracted from treated honeybee (Apis mellifera) colonies and toxicity to brood.

This study aimed to assess oxytetracycline (OTC) residue levels in honey up to 12 weeks after treatment of honeybee colonies with two methods of application (in liquid sucrose and in powdered icing sugar). Significantly greater mortality was seen in the all stages of brood development for the treated colonies when compared with the controls. Samples of honey were extracted up to 12 weeks after treatment and analysed by HPLC following metal chelation with a limit of quantitation of 0.05 mg/kg. These data showed that the current method of application of Terramycin in liquid form results in very high residue levels in honey with residues of 3.7 mg/kg eight weeks after application. Further work is required to determine whether the levels can be further reduced by changes in the method of application whilst ensuring efficacy and minimizing the effects on brood.