Tylosin tartrate and lincomycin hydrochloride effectively control strains of Paenibacillus larvae subsp. larvae resistant to oxytetracycline, the only registered antibiotic for control of brood diseases in Canada and the U.S. Though efficacious, these compounds are very stable in honey and potentially pose significant residue risks depending on their formulation, dosages and application methods to colonies. In northern climates this problem is compounded by a relatively short production season that permits minimal withdrawal for the drugs. To investigate these effects we conducted large-scale field experiments during 2002 and 2003 in which tylosin and lincomycin were applied to honey bee colonies as medicated sugar syrups, icing sugar dustings or as pollen patties in the spring. A target dose of 600 mg of antibiotic was used, however doses ranged from 400 to 3000 mg per colony. Beginning one week after the last application of antibiotics, 15 g honey samples were drawn from the brood nest and the honey supers at weekly intervals. Samples were analyzed for antibiotic residues using solid phase extraction followed by LC-ESI-MS/MS and also by a microbiological disk diffusion assay. Initial results indicate both drugs to be highly residual in honey, with the greatest residues resulting from medicated syrup formulations. Only syrup treatments or abusive dosages of the drugs in sugar dustings resulted in detectable residue production in honey destined for human consumption. Formulations of the drugs in pollen patties show promise for efficacious disease control at lower than target dosages with no residue hazard.
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