Transmission routes for DWV at the individual bee level within colonies. The vectorial transmission of DWV has been experimentally proven [52, 133]. Evidence for additional horizontal routes between nurse bees and larvae through larval food has also been provided . The best analyzed transmission route for DWV is the vectorial transmission through the ectoparasitic mite V. destructor. DWV is transmitted by mites to parasitized pupae and during the phoretic phase to adult bees. The mites in turn acquire DWV when feeding on infected pupae and adult bees. Non-viable bees exhibiting deformed wings as the most prominent clinical symptom only occur when DWV transmission to pupae via V. destructor initiated an overt infection.