4.1.1. Removing sealed brood
During spring and summer, when brood rearing is continuous and extensive, it is possible to increase mite infestations in colonies by removing sealed bee brood (i.e. pupae). This has been done regularly by numerous researchers (McMullan and Brown, 2005; G W Otis, pers. obs.; J Villa, pers. comm.). Confining bees in hives may also increase infestation of young workers, but this has not been tested. One challenge is to increase mite prevalence, yet not so much that winter survival is jeopardized. Because many heavily infested colonies die over winter, studying live mites often requires sampling hives in spring to find heavily infested colonies for experimentation. Several researchers have moved heavily infested colonies, only to subsequently find that the mite infestations declined drastically (J Pettis, pers. comm.; J McMullan, pers. comm.; G W Otis, pers. obs.). It is not known why this occurs, but suggested causes are overheating or chilling during transport, loss of infested bees due to their failure to return to their hives after orientation flights in new locations (J Pettis, pers. comm.), or emigration of infested bees from the nest (J McMullan, pers. comm.).