Coumaphos residue transfer to honey bee brood (Apis mellifera) in realistic scenarios

Coumaphos is a veterinary treatment administered for the control of Varroa destructor in honey bee colonies. The detection of its residues, however, has been frequently reported in beeswax. This study is pioneer to investigate whether the honey bee brood is exposed to coumaphos via contact or by ingestion of food resources due to a residue transfer inside the bee hive. This field study addresses two scenarios: 1) after its administration according to the posology using strips inside the bee hives and, 2) placing contaminated wax containing coumaphos at 10 mg/Kg into the bee hives (simulating the use of recycled wax). In bee bread, the average concentrations of residues (mean ± s.d.) were 246.66 ± 772.29 ng/g and 192.55 ± 320.19 ng/g in scenario 1 and 2, respectively. In honey, residue concentration was 1.98 ± 5.41 ng/g and 1.93 ± 6.59 ng/g. In scenario 2, exposure has led to residue detection in all larval stages at concentrations ranging from 51.93 to 383.42 ng/g (larvae), 42.20-58.54 ng/g (prepupae), 18.35-26.24 ng/g (pupae) to 21.92-35.92 ng/g (born bee). This study shows that there is a high risk for the bee brood (larvae) by ingestion of bee bread when the residue concentration is >251.31 ng/g. Residue levels in larvae or in prepupae >42.20 ng/g give rise to a moderate risk.