Nosema ceranae and Deformed Wing Virus infections ofhoney bees in a hoarding cage experiment

The multifactorial nature of colony losses is widely accepted, although synergistic effects of possible causative factors are not completely understood. To investigate interactions between two serious and wide-spread pathogens of honey bee colonies, Deformed Wing Virus and Nosema ceranae, an experiment was set up in which worker bees were infected with known amounts of N. ceranae spores. To reduce the impact of Varroa destructor an apiary was established in an isolated mountain area and mitelevels kept as low as possible. Newly emerged worker bees were kept in 14 hoarding cages (30 bees each). Each cage was provided with 0.2 ml 50% w/v sucrose solution containing20106 N. ceranae spores per ml. Oral infection was therefore obtained via bulk feeding. The number of dead bees in each cage was recorded for ~30 days. After 14 days from beginning of experiment, five live worker bees were removed from each cage. Midguts were removed for spore counts and at the same time, head and thorax of each worker were removed and subsequentlyanalysed for quantitative DWV analyses using standard RT PCR protocols. The data show a strong positive correlation between the number of N. ceranae spores and the number of DWV copies, suggesting that the two pathogens may interact synergistically. N. ceranae may enable oral infection by the virus by perforation of the midgut epithelium, or increase replication of the virus by suppression of the immune system.