Resources that SHB acquired DWV. A 702-bp long band indicating DWV-infection was found in SHB that were kept on dead workers with clinical symptoms (lanes 2-4), on DWV positive brood (lanes 5-7), on contaminated wax (lanes 8-10) and in the positive control (lane 18). No band was obtained for the SHB that were kept on pollen (lanes 11-13), on sugar water (= controls; lanes 14-16) and in the negative control (lane 17; lane 1: 100-bp DNA ladder).